Green tea contains only a small amount of caffeine, so people can enjoy it as an alternative to black tea or coffee. Drinking it may also strengthen the immune system.

As with blueberries, green tea contains flavonoids, which may reduce the risk of a cold. Kefir is a fermented drink that contains live cultures of bacteria that are beneficial for health.

Initial research suggests that drinking kefir may boost the immune system. According to a review , various studies have shown that regular consumption of kefir can help with:.

The majority of the research that supports this was carried out on animals or in a laboratory. Researchers need to perform additional studies to understand how kefir may prevent disease in humans. Sunflower seeds can make a tasty addition to salads or breakfast bowls.

They are a rich source of vitamin E , an antioxidant. In the same way as other antioxidants, vitamin E improves immune function. It does this by fighting off free radicals, which can damage cells.

Almonds are another excellent source of vitamin E. They also contain manganese, magnesium , and fiber. A small handful or a quarter of a cup of almonds is a healthful snack that may benefit the immune system.

Oranges and kiwis are an excellent source of vitamin C, which is the vitamin that many people turn to when they feel a cold developing.

While scientists are still not sure exactly how it helps, vitamin C may reduce the duration of common cold symptoms and improve the function of the human immune system. For people trying to avoid the sugar in fruit, red bell peppers are an excellent alternative source of vitamin C.

Stir-frying and roasting both preserve the nutrient content of red bell peppers better than steaming or boiling, according to a study on cooking methods.

That said, it is important to remember that the immune system is complex. Eating a healthful, balanced diet is just one way to support immune health. It is also essential to be mindful of the other lifestyle factors that may affect immune system health, such as exercising and not smoking.

Anyone who gets frequent colds or other illnesses and is concerned about their immune system should speak to a doctor. In this article, we describe types of foods that may weaken the immune system and others that may help support it. Learn more here. What are the best ways to boost the immune system and can they give you enhanced protection against infections and diseases?

We take a look. While no drinks can quickly give the immune system a boost, staying hydrated and getting plenty of nutrients is essential for immune function. Elderberry supplements may help support immune system health.

The immune system defends the body from invaders such as viruses, bacteria, and foreign bodies. Find out how it works, what can go wrong, and how to….

My podcast changed me Can 'biological race' explain disparities in health? Broccoli is supercharged with vitamins and minerals. Packed with vitamins A, C, and E, as well as fiber and many other antioxidants , broccoli is one of the healthiest vegetables you can put on your plate.

The key to keeping its power intact is to cook it as little as possible — or better yet, not at all. Research has shown that steaming or microwaving are the best ways to keep more nutrients in the food.

Garlic adds flavor to food and has long been used for medicinal purposes. Early civilizations recognized its value in fighting infections. Garlic may also slow down hardening of the arteries, and people use it to treat high blood pressure. Ginger is another ingredient many turn to after getting sick.

Ginger may help decrease inflammation, which can help reduce a sore throat and inflammatory illnesses. It may also help with nausea. Ginger may also decrease chronic pain and might even possess cholesterol-lowering properties.

Similar to broccoli, spinach is healthiest when cooked as little as possible so that it retains its nutrients. However, light cooking makes it easier to absorb the vitamin A and allows other nutrients to be released from oxalic acid , an antinutrient.

Check out some spinach recipes here. These cultures may stimulate your immune system to help fight diseases. Try to get plain yogurts rather than the kind that are flavored and loaded with sugar. You can sweeten plain yogurt yourself with healthy fruits and a drizzle of honey instead.

Yogurt can also be a great source of vitamin D , so try to select brands fortified with this vitamin. Clinical trials are even in the works to study its possible effects on COVID Research so far suggests that vitamin D deficiency may increase the risk for COVID19 and the severity of disease progression in people with the infection.

Experts therefore believe supplementation may protect people with a vitamin D deficiency. However, there is no evidence that vitamin D can treat a COVID19 infection.

When it comes to preventing and fighting off colds, vitamin E tends to take a backseat to vitamin C. However, this powerful antioxidant is key to a healthy immune system.

Nuts, such as almonds , are packed with the vitamin and also have healthy fats. Adults only need about 15 mg of vitamin E each day.

Sunflower seeds are full of nutrients, including phosphorous , magnesium , and vitamins B6 and E. Vitamin E is important in regulating and maintaining immune system function. Other foods with high amounts of vitamin E include avocados and dark leafy greens.

Sunflower seeds are also high in selenium. Just 1 ounce contains nearly half the selenium that the average adult needs daily. A variety of studies , mostly performed on animals, have looked at its potential to combat viral infections such as swine flu H1N1. You may know turmeric as a key ingredient in many curries.

This bright yellow, bitter spice has also been used for years as an anti-inflammatory in treating both osteoarthritis and rheumatoid arthritis. Research shows that high concentrations of curcumin , which gives turmeric its distinctive color, can help decrease exercise-induced muscle damage.

Curcumin has promise as an immune booster based on findings from animal studies with antimicrobial properties. More research is needed.

Both green and black teas are packed with flavonoids , a type of antioxidant. Where green tea really excels is in its levels of epigallocatechin gallate EGCG , another powerful antioxidant.

Research has suggested that EGCG may have antiviral properties that support the immune system. In a large bowl, toss together remaining ingredients, except for grapefruit and orange segments. Divide salad between two plates. Top with cod and citrus pieces, and black pepper to taste.

Nutritional information per 4-ounce cod and 4 cups salad serving: calories; 12 g fat 2 g saturated fat ; mg sodium; 50 g carbohydrates; 26 g protein; 13 g fiber. Nutritional information per 3-tablespoon serving: 53 calories; 2 g fat 0 g saturated fat ; mg sodium; 7 g carbohydrates; 2 g protein; 2 g fiber.

Recipes from mayoclinic. Jamie L. Pronschinske is a dietitian in La Crosse , Wisconsin. Skip to main content. Posted By. Jamie Pronschinske, RDN, CD Nutrition. Recent Posts. Speaking of Health. Topics in this Post. A few key micronutrients have been identified as critical for the growth and function of immune cells, including: Iron Iron is a component of enzymes critical for immune cell function.

Sources include red meat, beans, nuts and fortified breakfast cereals. Vitamin A Vitamin A helps protect against infections by keeping skin and tissues in the mouth, stomach, intestines and respiratory system healthy.

Sources include orange and red fruits, and vegetables like carrots, apricots and bell peppers.

Making healthy choices and changing lifestyle habits can support a healthy immune system. Increasing plant-based foods which are naturally nutrient-rich, among other lifestyle changes, can also help the immune system fight illnesses.

Citrus fruits are rich in vitamin C, which supports a healthy immune system. Vitamin C is an antioxidant that can help with wound healing, protect the epithelial barrier against pathogens and can trigger anti-inflammatory signals.

Some studies have shown that vitamin C appears to prevent and treat respiratory and systemic infections. It can also help to reduce the length of cold symptoms, but cannot prevent someone from catching a cold. Adding citrus fruits to your meal is the way to go this season.

Oats contain many nutrients and bioactive compounds, such as polyphenolics, which have been associated with antioxidant, anti-inflammatory and immunogenic responses.

Oats also contain dietary fibers and beta-glucan that help modulate the immune system, which is paramount for defending against infectious disease, including cold, flu and COVID Oats can also help optimize the immune system indirectly by modifying the content of microbiota.

All forms of oatmeal contain the same vitamins, minerals, phytochemicals and fiber. A good breakfast to help fight infections can be a warm oatmeal made with steel-cut, rolled oats, or unflavored instant oatmeal.

Start by placing the salmon on an aluminum foil or parchment paper-lined baking sheet. Top the salmon with some lemon juice, olive oil and fresh dill. Season lightly with salt, pepper and garlic.

Bake for 30 minutes at degrees. You can also serve this dish with some cooked vegetables and wild rice. A smoothie is a great way to blend a variety of different nutritious ingredients. To make this smoothie, blend together kale and berries with some coconut water or plant-based milk. You can also add some nutritious herbs like ginger and turmeric for extra benefits.

Kale is a superfood , full of nutrients like vitamin A, vitamin B6, vitamin K, folate and fiber and berries are packed with powerful antioxidants like vitamin C. In addition to incorporating immune-boosting foods into your diet, there are a variety of other lifestyle habits you can choose to support your immune system as well.

Choosing healthy habits can help to lower your stress levels, reduce inflammation and improve your overall health and well-being. Getting enough hours of sleep is essential for proper immune function. During sleep your body repairs and regenerates immune cells. You want to make sure that you are not only sleeping enough but also getting restorative sleep—this means that when you wake up you actually feel rested.

Take steps to get high-quality sleep such as going to bed at a reasonable hour and creating a comfortable sleep environment. Regular exercise helps to keep your body functioning properly and reduces inflammation to help support immune function.

Try to incorporate daily exercise into your routine by walking, jogging or doing a circuit workout most days of the week. You should also do some strength training exercises like weight lifting a couple of times a week as well.

Chronic stress can suppress immune function and make you more susceptible to illness and infection. Many people experience chronic stress which interferes with their daily lives.

Try using some stress management techniques such as deep breathing, yoga, meditation and exercise to help reduce your stress levels. Frequent hand washing is one of the best ways to prevent sickness since it helps you reduce your exposure to illness-causing bacteria and germs.

Wash your hands frequently throughout the day and try to limit your exposure to sick individuals to prevent sickness. Unhealthy habits like smoking and excessive alcohol consumption can reduce your immune function and make you more likely to get sick. Quitting both of these habits will have a variety of other health benefits outside of just improving your immune function so it is entirely worth the effort it takes.

Incorporating healthy lifestyle habits into your routine will have a lasting impact on your overall health and it will help you feel your best. Take steps to incorporate immune-boosting foods and healthy habits into your daily routine to prevent sickness and keep your immune system functioning optimally.

Water intake can have many positive benefits for your immune system, including but not limited to aiding in digestion and preventing possible pathogens like a virus or bacteria from getting into the eyes, nose and mouth.

Prioritizing exercise. Moderate-intensity exercise can help maintain a healthy immune system. Getting enough sleep. If you get enough sleep, it will help your body fight off sickness and help succeed at the tips mentioned above. Adults should get between hours of sleep each night.

Increasing vitamin intake. Vitamins B6, C and E are all known for their immune-boosting properties. Some foods rich in these vitamins include eggs, bell peppers, spinach and almonds.

Adaptive or acquired immunity is a system that learns to recognize a pathogen. It is regulated by cells and organs in our body like the spleen, thymus, bone marrow, and lymph nodes. When a foreign substance enters the body, these cells and organs create antibodies and lead to multiplication of immune cells including different types of white blood cells that are specific to that harmful substance and attack and destroy it.

Our immune system then adapts by remembering the foreign substance so that if it enters again, these antibodies and cells are even more efficient and quick to destroy it. Antigens are substances that the body labels as foreign and harmful, which triggers immune cell activity.

Allergens are one type of antigen and include grass pollen, dust, food components, or pet hair. Antigens can cause a hyper-reactive response in which too many white cells are released.

For example, an allergy to mold triggers symptoms of wheezing and coughing in a sensitive individual but does not trigger a reaction in other people. When pathogens attack healthy cells and tissue, a type of immune cell called mast cells counterattack and release proteins called histamines, which cause inflammation.

Inflammation may generate pain, swelling, and a release of fluids to help flush out the pathogens. The histamines also send signals to discharge even more white blood cells to fight pathogens.

However, prolonged inflammation can lead to tissue damage and may overwhelm the immune system. Autoimmune disorders like lupus, rheumatoid arthritis, or type 1 diabetes are partly hereditary and cause hypersensitivity in which immune cells attack and destroy healthy cells.

Immunodeficiency disorders can depress or completely disable the immune system, and may be genetic or acquired. Acquired forms are more common and include AIDS and cancers like leukemia and multiple myeloma. Eating enough nutrients as part of a varied diet is required for the health and function of all cells, including immune cells.

Certain dietary patterns may better prepare the body for microbial attacks and excess inflammation, but it is unlikely that individual foods offer special protection. Examples of nutrients that have been identified as critical for the growth and function of immune cells include vitamin C, vitamin D, zinc, selenium, iron, and protein including the amino acid glutamine.

Diets that are limited in variety and lower in nutrients, such as consisting primarily of ultra-processed foods and lacking in minimally processed foods, can negatively affect a healthy immune system.

It is also believed that a Western diet high in refined sugar and red meat and low in fruits and vegetables can promote disturbances in healthy intestinal microorganisms, resulting in chronic inflammation of the gut, and associated suppressed immunity. The microbiome is an internal metropolis of trillions of microorganisms or microbes that live in our bodies, mostly in the intestines.

It is an area of intense and active research, as scientists are finding that the microbiome plays a key role in immune function.

The gut is a major site of immune activity and the production of antimicrobial proteins. A high-fiber plant-rich diet with plenty of fruits, vegetables, whole grains, and legumes appear to support the growth and maintenance of beneficial microbes.

Certain helpful microbes break down fibers into short chain fatty acids, which have been shown to stimulate immune cell activity. These fibers are sometimes called prebiotics because they feed microbes.

Therefore, a diet containing probiotic and prebiotic foods may be beneficial. Probiotic foods contain live helpful bacteria, and prebiotic foods contain fiber and oligosaccharides that feed and maintain healthy colonies of those bacteria.

Animal studies have found that deficiencies in zinc , selenium , iron , copper, folic acid , and vitamins A , B6 , C , D , and E can alter immune responses. Epidemiological studies find that those who are poorly nourished are at greater risk of bacterial, viral, and other infections.

Eating a good quality diet, as depicted by the Healthy Eating Plate, can prevent deficiencies in these nutrients. However, there are certain populations and situations in which one cannot always eat a variety of nutritious foods, or who have increased nutrient needs.

In these cases a vitamin and mineral supplement may help to fill nutritional gaps. Studies have shown that vitamin supplementation can improve immune responses in these groups.

The elderly are a particularly high-risk group. The immune response generally declines with increasing age as the number and quality of immune cells decreases. This causes a higher risk of poorer outcomes if the elderly develop chronic or acute diseases.

In addition, about one-third of elderly in industrialized countries have nutrient deficiencies. Diet variety may also be limited due to budget constraints or lower interest in cooking for one person; poor dentition; mental impairment; or lack of transportation and community resources to obtain healthy food.

Megadose supplements many times the RDA do not appear justified, and can sometimes be harmful or even suppress the immune system e.

Remember that vitamin supplements should not be considered a substitute for a good diet because no supplements contain all the benefits of healthful foods. Several herbal supplements have been suggested to boost immune function.

What does the research say? Diet Review: Anti-Inflammatory Diet. Food Safety, Nutrition, and Wellness during COVID Ask the Expert: The role of diet and nutritional supplements during COVID The contents of this website are for educational purposes and are not intended to offer personal medical advice.

You should seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.

The Nutrition Source does not recommend or endorse any products. Skip to content The Nutrition Source. The Nutrition Source Menu. Search for:. Home Nutrition News What Should I Eat? What Is Our Immune System? These barriers include: Skin that keeps out the majority of pathogens Mucus that traps pathogens Stomach acid that destroys pathogens Enzymes in our sweat and tears that help create anti-bacterial compounds Immune system cells that attack all foreign cells entering the body Adaptive or acquired immunity is a system that learns to recognize a pathogen.

Other conditions that trigger an immune response Antigens are substances that the body labels as foreign and harmful, which triggers immune cell activity. What factors can depress our immune system?

Older age: As we age, our internal organs may become less efficient; immune-related organs like the thymus or bone marrow produce less immune cells needed to fight off infections. Observational studies show associations between low vitamin D status and increased risk of pulmonary tuberculosis and mortality in people with HIV [ ].

In addition, low levels of vitamin D in pregnant people with HIV are associated with poor fetal and infant growth [ ]. Results from clinical trials, however, have not shown that vitamin D supplementation improves outcomes in people with HIV [ , ].

Vitamin D3 supplementation did not affect rates of mortality or pulmonary tuberculosis. Moreover, vitamin D3 supplementation did not affect secondary outcomes, including risk of HIV progression, viral suppression, comorbidities nausea, vomiting, cough, fever, or diarrhea , changes in body weight, or depression [ ].

Another clinical trial in Tanzania examined the effects of vitamin D3 supplementation during pregnancy and lactation in 2, people with HIV [ ]. Vitamin D3 supplementation did not affect the risk of maternal HIV progression or death.

The results also showed no difference in the risk of small-for-gestational-age birth or of infant stunting at 1 year. Daily intakes of up to 25— mcg 1, IU—4, IU vitamin D, depending on age, in foods and dietary supplements are safe for infants and children, and up to mcg 4, IU is safe for adults, including those who are pregnant or lactating [ 78 ].

These ULs, however, do not apply to people taking vitamin D under the care of a physician. Higher intakes usually from supplements can lead to nausea, vomiting, muscle weakness, confusion, pain, loss of appetite, dehydration, excessive urination and thirst, and kidney stones.

In extreme cases, vitamin D toxicity causes renal failure, calcification of soft tissues throughout the body including in coronary vessels and heart valves , cardiac arrhythmias, and even death [ ].

Several types of medications might interact with vitamin D. For example, orlistat, statins, and steroids can reduce vitamin D levels [ , ]. In addition, taking vitamin D supplements with thiazide diuretics might lead to hypercalcemia [ ]. More information on vitamin D is available in the ODS health professional fact sheet on vitamin D.

For information on vitamin D and COVID, please see the ODS health professional fact sheet, Dietary Supplements in the Time of COVID Vitamin E, also called alpha-tocopherol, is an essential nutrient that is present in several foods , including nuts, seeds, vegetable oils, and green leafy vegetables.

The RDA for vitamin E is 4 to 15 mg for infants and children, depending on age, and 15 to 19 mg for adults, including those who are pregnant or lactating [ 56 ]. Vitamin E is an antioxidant that plays an important role in immune function by helping maintain cell membrane integrity and epithelial barriers and by enhancing antibody production, lymphocyte proliferation, and natural killer cell activity [ 4 , 5 , 15 , 17 , 25 , 58 , 79 , ].

Vitamin E also limits inflammation by inhibiting the production of proinflammatory cytokines [ ]. Human and animal studies suggest that vitamin E deficiency impairs humoral and cell-mediated immunity, is associated with reduced natural killer cell activity, and increases susceptibility to infections [ 5 , , ].

Frank vitamin E deficiency is rare, except in people with intestinal malabsorption disorders [ 56 , 79 ]. Research on the ability of vitamin E to improve immune function tends to use supplemental vitamin E rather than simply ensuring that study participants achieve adequate vitamin E status because it is thought that higher doses may be needed to achieve beneficial effects [ ].

However, study findings have been mixed. However, vitamin E supplementation did not affect the risk of death from pneumonia within 30 days of the initial hospitalization.

A few clinical trials that have examined the effects of vitamin E supplementation on respiratory tract infections in infants and young children or in older adults suggest that vitamin E offers limited benefits and might even increase symptom severity.

A clinical trial in a low-income urban area in India examined the effects of mg alpha-tocopherol and mg ascorbic acid twice daily or placebo for 5 days in infants and young children age 2 to 35 months who were hospitalized with severe acute lower respiratory tract infections and receiving standard care [ ].

Supplementation did not affect the time required to recover from illness. Another clinical trial in which healthy men and women age 60 years or older took one of four different treatments daily for about 15 months identified no benefits and, in fact, found potential risks of vitamin E supplementation to prevent respiratory tract infections.

All but one of the participants had adequate vitamin E concentrations at the start of the study. The vitamin E supplements did not affect the incidence of acute respiratory tract infections throughout the trial. Moreover, participants who took the vitamin E supplement had longer durations of illness, more severe symptoms including fever and activity restrictions , and greater numbers of symptoms than those who did not take vitamin E.

Results were also negative in a similar trial in adults age 65 or older living in nursing homes to determine whether daily supplementation with IU vitamin E 91 mg, as dl -alpha-tocopherol for 1 year reduced the risk of upper or lower respiratory tract infections [ ].

Vitamin E supplementation did not affect the incidence of upper or lower respiratory tract infections or the total durations of the infections. Vitamin E supplementation for a median of 6. Among the 5, participants who smoked more than 19 cigarettes per day or did not exercise, however, vitamin E supplementation did not affect the risk of pneumonia.

All intake levels of vitamin E found naturally in foods are considered safe. These ULs, however, do not apply to people taking vitamin E under the care of a physician.

Vitamin E supplementation might interact with certain medications, including anticoagulant and antiplatelet medications. It might also reduce the effectiveness of radiation therapy and chemotherapy by protecting tumor cells from the action of these agents [ 76 , , ].

More information on vitamin E is available in the ODS health professional fact sheet on vitamin E. For information on vitamin E and COVID, please see the ODS health professional fact sheet, Dietary Supplements in the Time of COVID Selenium is an essential mineral contained in many foods , including Brazil nuts, seafood, meat, poultry, eggs, and dairy products as well as bread, cereals, and other grain products.

The RDA for selenium is 15 to 70 mcg for infants and children, depending on age, and 55 to 70 mcg for adults, including those who are pregnant or lactating [ 56 ]. Human and animal studies suggest that selenium helps support both the innate and adaptive immune systems through its role in T-cell maturation and function and in natural killer cell activity [ 2 , 25 , 58 , ].

It may also reduce the risk of infections [ 2 , 15 , 25 , 58 , ]. As a component of enzymes that have antioxidant activities, selenium might help reduce the systemic inflammatory response that can lead to ARDS and organ failure [ 27 , 58 , , ]. Low selenium status in humans has been associated with lower natural killer cell activity, increased risk of some bacterial infections, and increased virulence of certain viruses, including hepatitis B and C [ 2 , 5 , 10 , 15 , 27 , , , ].

However, evidence is conflicting whether selenium supplementation enhances immunity against pathogens in humans [ ]. Studies have also examined whether intravenous selenium which is classified as a drug in the United States benefits adults with sepsis; those who are critically ill and requiring mechanical ventilation; adults who are undergoing elective major surgery; or those who are critically ill from burns, head injury, brain hemorrhage, or stroke [ , , ].

The results of these studies provide no clear evidence of benefit. Selenium status varies by geographic region because of differences in the amounts of selenium in soil and in local foods consumed [ 56 , ].

Selenium deficiency is very rare in the United States and Canada, but low selenium status is common in some areas of the world, such as parts of Europe and China [ , ].

In children and adults with HIV, selenium deficiency is associated with a higher risk of morbidity and mortality [ ]. However, studies that examined whether micronutrient supplementation, including selenium, affects risk of HIV transmission or disease outcomes in children and adults have had mixed results.

An observational study in Thailand did not identify associations between selenium status in children with HIV and treatment outcomes [ ]. This study included boys and girls with HIV median age 7. Baseline selenium levels all of which were adequate showed no associations with ART treatment outcomes.

Clinical trials have found limited beneficial effects of selenium supplementation on immune function in people with HIV. Selenium supplementation provided no benefits in another trial that randomized men and women with HIV mean age Two Cochrane Reviews also concluded that selenium supplements offer little, if any, benefit for people with HIV.

The authors found that evidence was insufficient to determine whether supplementation with selenium alone is beneficial. Researchers have also examined whether blood selenium levels or selenium supplementation affect pregnancy outcomes in people with HIV.

Findings from these studies suggest that low blood selenium levels are associated with a higher risk of preterm delivery and that selenium supplementation might reduce the risk of preterm delivery but has mixed effects on other outcomes.

For example, a cross-sectional study in Nigeria of pregnant individuals age 15—49 years with HIV found that those with a selenium deficiency defined as blood selenium less than 0. In a clinical trial in Nigeria, researchers examined whether selenium supplementation affects pregnancy outcomes and disease progression in 90 pregnant individuals mean age These ULs, however, do not apply to people taking selenium under the care of a physician.

Higher intakes of selenium can cause a garlic odor in the breath and a metallic taste in the mouth as well as hair and nail loss or brittleness [ 56 ]. Other signs and symptoms of excess selenium intakes include nausea, diarrhea, skin rashes, mottled teeth, fatigue, irritability, and nervous system abnormalities.

Cisplatin, a chemotherapy agent used to treat ovarian, bladder, lung, and other cancers, can reduce selenium levels in hair, plasma, and serum [ , ]. The evidence from studies examining whether selenium supplementation helps reduce the side effects of cisplatin and other chemotherapy agents is uncertain [ , ].

More information on selenium is available in the ODS health professional fact sheet on selenium. For information on selenium and COVID, please see the ODS health professional fact sheet, Dietary Supplements in the Time of COVID Zinc is an essential nutrient contained in a wide variety of foods , including oysters, crab, lobster, beef, pork, poultry, beans, nuts, whole grains, and dairy products.

The RDA for zinc is 2—13 mg for infants and children, depending on age, and 8—12 mg for adults, including those who are pregnant or lactating [ 29 ]. Zinc is involved in numerous aspects of cellular metabolism. It is necessary for the catalytic activity of approximately enzymes and it plays a role in many body processes, including both the innate and adaptive immune systems [ 2 , 5 , 29 , 58 , ].

Zinc also has antiviral and anti-inflammatory properties, and it helps maintain the integrity of tissue barriers, such as the respiratory epithelia [ 5 , 58 , 83 , ].

Zinc deficiency adversely affects immune function by impairing the formation, activation, and maturation of lymphocytes. In addition, zinc deficiency decreases ratios of helper to suppressor T cells, production of interleukin-2, and activity of natural killer cells and cytotoxic T cells [ 2 , 4 , 5 , 27 , , , ].

Furthermore, zinc deficiency is associated with elevated levels of proinflammatory mediators [ ]. These effects on immune response probably increase susceptibility to infections [ ] and inflammatory diseases, especially those affecting the lungs [ ]. Studies have found associations between low zinc status and higher risk of viral infections [ 79 ], and people with zinc deficiency have a higher risk of diarrhea and respiratory diseases [ 2 ].

Poor zinc status is also common among people with HIV or hepatitis C and is a risk factor for pneumonia in older adults [ 27 , 58 , , , ]. Some research suggests that zinc supplementation increases the number of T cells in the blood of older adults living in nursing homes [ ].

population might obtain marginal amounts of zinc [ ]. Older adults are among the groups most likely to have low intakes. Researchers have hypothesized that zinc could reduce the severity and duration of cold symptoms by directly inhibiting rhinovirus binding and replication in the nasal mucosa and suppressing inflammation [ , ].

In studies of the effects of zinc supplements on the common cold, zinc is usually administered in a lozenge or syrup that temporarily sticks to the mouth and throat, placing the zinc in contact with the rhinovirus in those areas.

The results from clinical trials that have examined the effects of supplemental zinc on the common cold have been inconsistent. Overall, however, supplemental zinc in lozenge or syrup form appears to reduce the duration, but not the severity, of signs and symptoms of the common cold when taken shortly after a person develops a cold [ ].

In one clinical trial that found beneficial effects of zinc on the common cold, 50 adults took a zinc acetate lozenge In comparison with placebo, the zinc lozenges reduced the duration of colds by 3 days and the severity of cold symptoms cough, nasal discharge, and muscle aches [ ].

Results were more mixed in another clinical trial in which adults with experimentally induced colds took lozenges containing zinc gluconate Illnesses lasted 1 day less with the zinc gluconate lozenges than with the placebo, but the lozenges had no effect on symptom severity.

Furthermore, the 5. In a second trial described in the same report, neither zinc gluconate nor zinc acetate lozenges affected the duration or severity of cold symptoms in comparison with placebo in adults with colds [ ].

A systematic review and meta-analysis found that zinc appears to reduce the duration of the common cold but has mixed effects on the severity of signs and symptoms [ ]. It included 28 clinical trials including the three described above with a total of 5, participants mostly adults younger than 65 years who had a community-acquired viral respiratory tract infection or were inoculated with a rhinovirus.

Most trials provided zinc in the form of zinc acetate or gluconate lozenges with total daily zinc doses of 45 to mg for up to 2 weeks, but some trials used nasal sprays or gels. In participants who used products containing zinc, symptoms resolved an average of 2 days earlier than in those who took a placebo.

Zinc also reduced the severity of symptoms on the third day of illness. However, average daily symptom severity did not differ between those who were and were not treated with zinc supplements.

In addition, zinc did not affect the risk of developing a cold after rhinovirus inoculation. Other recent systematic reviews and meta-analyses have also found that zinc shortens the duration of the signs and symptoms of colds but does not reduce the risk of colds [ 54 , 67 , ].

Poor zinc status is associated with greater susceptibility to pneumonia, more severe disease, and higher mortality risk in children [ ].

Several clinical trials have examined the effects of zinc supplementation on the incidence of pneumonia and as an adjunctive treatment for pneumonia. However, most research suggests that the adjunctive use of zinc supplements to treat pneumonia in children does not affect mortality or time to recovery.

A systematic review and meta-analysis included 11 clinical trials in children age 2 to 60 months with mostly severe pneumonia in low- and middle-income countries [ ]. Another meta-analysis of six placebo-controlled trials that included 2, children age 2 to 60 months found that zinc supplementation reduced mortality rates from severe pneumonia but not rates of treatment failure or changes in antibiotic therapy [ ].

Diarrhea is associated with high mortality rates among children in low-income countries, where it causes about , deaths annually [ , ].

Zinc supplementation may benefit children with acute diarrhea, especially in low-income countries, where zinc deficiency is common.

Clinical trials show that zinc supplementation helps shorten the duration of diarrhea in children in low-income countries. A Cochrane Review included 33 trials that compared the effects of zinc supplementation with those of placebo in 10, children age 1 month to 5 years who had acute or persistent diarrhea [ ].

Most studies were conducted in Asian countries that had high rates of zinc deficiency. Zinc was administered in the form of zinc acetate, zinc gluconate, or zinc sulphate.

In addition, evidence that the authors deemed to have high certainty showed that zinc supplementation reduces the duration of diarrhea in children with signs of malnutrition by about a day. In children younger than 6 months, however, zinc supplementation did not affect mean duration of diarrhea or persistence of diarrhea for 7 days.

A systematic review and meta-analysis had similar findings. It examined the use of zinc alone or in combination with other treatments for acute diarrhea and gastroenteritis in studies in 32, children, mostly from low- and middle-income countries [ ]. Analyses showed that zinc alone or in combination reduced the duration of diarrhea by about ¾ to 1½ days.

The authors concluded that zinc was one of the most effective interventions of those examined, especially when it was combined with Saccharomyces boulardii a probiotic or smectite a natural clay that contains minerals , for reducing the duration of acute diarrhea and gastroenteritis in children.

The WHO and UNICEF recommend supplementation with 20 mg zinc per day, or 10 mg for infants younger than 6 months, for 10 to 14 days to treat acute childhood diarrhea [ ]. However, most trials of zinc supplementation for diarrhea have been conducted in low-income countries [ ].

In well-nourished children, zinc supplements might have only a marginal effect on diarrhea duration. HIV infection reduces the absorption and metabolism of zinc from foods [ ].

In addition, people with HIV often have diarrhea, which can result in excessive losses of zinc. For these reasons, people with HIV often have low plasma or serum zinc levels. Several clinical trials have found some beneficial effects of zinc supplementation to manage the morbidity and mortality associated with HIV infection.

However, findings were less positive in two Cochrane Reviews and another trial not included in either Cochrane Review that assessed the potential benefits of supplementation with micronutrients, including zinc, or placebo in various populations with HIV. However, zinc supplementation did not affect viral load or mortality rates in this second trial.

However, the supplements blunted the rise in hemoglobin concentrations between baseline and 6 weeks after delivery. These ULs, however, do not apply to people taking zinc under the care of a physician.

Higher intakes can cause nausea, vomiting, loss of appetite, abdominal cramps, diarrhea, headaches, and a metallic taste in the mouth [ 29 , 32 ]. In clinical trials in children, zinc supplementation to treat diarrhea increased the risk of vomiting more than placebo [ , ].

Zinc supplements might interact with several types of medications. For example, zinc can reduce the absorption of some types of antibiotics and penicillamine, a drug used to treat rheumatoid arthritis [ , ]. Other medications, such as thiazide diuretics and certain antibiotics, can reduce zinc absorption [ , ].

More information on zinc is available in the ODS health professional fact sheet on zinc. For information on zinc and COVID, please see the ODS health professional fact sheet, Dietary Supplements in the Time of COVID Andrographis paniculata , also known as Chuān Xīn Lián, is an herb that is native to subtropical and Southeast Asia [ ].

Its leaves and other aerial above-ground parts are used in traditional Ayurvedic, Chinese, and Thai medicine for relieving symptoms of the common cold, influenza, and other respiratory tract infections [ ]. The active constituents of andrographis are believed to be andrographolide and related compounds, which are diterpene lactones that might have antiviral, anti-inflammatory, and immune-stimulating effects [ , , ].

Results from several clinical trials suggest that andrographis might reduce the duration of upper respiratory tract infections and the severity of symptoms. One of these trials used a common andrographis preparation called Kan Jang. The trial included 50 men and women age 18 to 50 years with the common cold who took four tablets of Kan Jang each containing 85 mg of an andrographis extract three times daily for 5 days 1, mg total daily dose or placebo within 3 days of developing cold symptoms [ ].

Participants who took Kan Jang experienced milder symptoms, recovered sooner, and took fewer days of sick leave than those who took placebo. In another clinical trial, men and women age 18 to 60 years with upper respiratory tract infections took either KalmCold containing mg of an andrographis extract twice daily or placebo for 5 days [ ].

The results showed no differences in symptom severity during days 1 to 3 of treatment. However, between days 3 and 5, participants who took KalmCold experienced milder symptoms—including cough, nasal discharge, headache, fever, and sore throat but not earache —than those who took placebo.

Two systematic reviews and meta-analyses of clinical trials found that andrographis preparations had beneficial effects on symptoms and duration of the common cold.

The more recent of these analyses, published in , included 33 clinical trials including the two described above that evaluated the effects of andrographis alone or in combination with other herbs on symptoms of acute upper and lower respiratory tract infections in a total of 7, participants [ ].

Treatment protocols varied widely, but typical daily doses ranged from to 1, mg andrographis extract for 3 to 7 days; studies compared andrographis with placebo, usual care, or other herbal interventions. The analyses showed that andrographis significantly reduced the severity of cough, sore throat, and overall symptoms.

However, the authors noted that the findings should be interpreted with caution because the studies were heterogenous and many were of poor quality.

Similar findings were reported from a systematic review and meta-analysis [ ]. It included six clinical trials including the two described above that administered Kan Jang or KalmCold All studies in this analysis compared andrographis with placebo, not usual care or other herbal interventions as in the meta-analysis described above.

Andrographis reduced the frequency and severity of cough to a greater extent than placebo. Three earlier systematic reviews also showed that andrographis appears to alleviate symptoms of upper respiratory tract infections [ , , ]. Although these findings suggest that andrographis might be useful to manage the symptoms and reduce the duration of upper respiratory tract infections, the evidence has several weaknesses.

For example, the studies used different andrographis formulations, and many of the clinical trials were conducted by investigators affiliated with the manufacturer of Kan Jang or KalmCold [ , ].

Clinical trials have found minor adverse effects, including nausea, vomiting, vertigo, skin rashes, diarrhea, and fatigue [ , , ]. Allergic reactions might also occur [ , ].

Findings from some animal studies suggest that andrographis might adversely affect fertility, so experts recommend against its use by men and women during the preconception period and by people who are pregnant [ , , ].

According to animal and laboratory studies, andrographis might decrease blood pressure and inhibit platelet aggregation, so it could interact with antihypertensive and anticoagulant medications by enhancing their effects [ ].

Because of its potential immune-stimulating effects, andrographis might also reduce the effectiveness of immunosuppressants [ , ]. For information on andrographis and COVID, please see the ODS health professional fact sheet, Dietary Supplements in the Time of COVID Echinacea, commonly known as purple coneflower, is an herb that grows in North America and Europe [ ].

Although the genus Echinacea has many species, extracts of E. purpurea , E. angustifolia , and E. pallida are the most frequently used in dietary supplements. The echinacea supplements on the market in the United States often contain extracts from multiple species and plant parts [ ].

Echinacea contains volatile terpenes, polysaccharides, polyacetylenes, alkamides, phenolic compounds, caffeic acid esters, and glycoproteins [ ]. Echinacea might have antibacterial activities, stimulate monocytes and natural killer cells, and inhibit virus binding to host cells [ 3 , ].

It might also reduce inflammation by inhibiting inflammatory cytokines [ 3 ]. Most studies of echinacea have assessed whether it helps prevent and treat the common cold and other upper respiratory illnesses, but it has also been used in traditional medicine to promote wound healing [ , ].

Results from clinical trials examining the effects of echinacea for the common cold have been mixed. Overall, studies suggest echinacea might slightly reduce the risk of developing a cold but does not shorten the duration or severity of illness. For example, one clinical trial examined the effects of echinacea on the risk of the common cold in men and women mean age 23 years [ ].

purpurea extract Echinaforce or placebo; if participants came down with a cold during the study, they increased their dose to 4, mg per day. Participants taking echinacea had fewer colds and fewer days with cold symptoms than those taking a placebo.

Another clinical trial examined whether echinacea helps treat the common cold in male and female participants age 12 to 80 years who developed cold symptoms within 36 hours before enrollment [ ].

Participants took E. purpurea and E. angustifolia extracts four times a day for a combined dose of 10, mg during the first 24 hours and then 5, mg for 4 days or placebo. Echinacea did not shorten illness duration or severity.

A systematic review and meta-analysis examined the effects of echinacea E. purpurea , E angustifolia , E. pallida , or more than one form to prevent upper respiratory tract infections or reduce the duration of illness [ ]. Nine clinical trials eight in adults and one in children were included in the prevention meta-analysis portion of this analysis, and seven all in adults were included in the duration meta-analysis, including the two trials described above [ , ].

A Cochrane Review of echinacea use for preventing and treating the common cold had similar results [ ]. The review included 24 clinical trials with a total of 4, participants. Limited research has also examined whether echinacea is beneficial for influenza.

One clinical trial found that echinacea had similar effects to oseltamivir Tamiflu , a medication used to treat influenza. This trial included male and female participants age 12 to 70 who had had influenza symptoms for up to 48 hours [ ]. Participants took either E. The results showed no difference between E.

Purpurea and oseltamivir followed by placebo in rapidity of recovery from influenza after 1 day, 5 days, or 10 days of treatment. In addition, participants taking echinacea experienced fewer adverse events, especially nausea and vomiting. Additional research is needed to confirm this finding.

Echinacea appears to be safe. In rare cases, echinacea can cause allergic reactions [ ]. The safety of echinacea during pregnancy is not known, so experts recommend against the use of echinacea supplements by people who are pregnant [ ]. Echinacea might interact with several medications.

For example, echinacea might increase cytochrome P activity, thereby reducing levels of some drugs metabolized by these enzymes [ ]. In addition, echinacea might reduce the effectiveness of immunosuppressants due to its potential immunostimulatory activity [ ].

For information on echinacea and COVID, please see the ODS health professional fact sheet, Dietary Supplements in the Time of COVID Elderberry contains many compounds—including anthocyanins, flavonols, and phenolic acids—that might have anti-inflammatory, antiviral, antimicrobial, and immune-stimulating effects [ 3 , ].

Studies of the effects of elderberry have primarily used elderberry extracts, not the berries themselves [ ]. Components of elderberry might help prevent respiratory infections by inhibiting virus binding to host cells and by stimulating the immune system [ ].

A few clinical trials have examined the effects of elderberry on the common cold and influenza. The results from these trials have been mixed. However, overall, they suggest that elderberry might help relieve symptoms of respiratory tract infections.

One clinical trial examined whether elderberry extract helps prevent and treat the common cold [ ]. Elderberry extract did not reduce the number of participants who developed a cold.

However, among participants who did develop a cold, elderberry extract reduced cold duration by about 2 days and reduced the severity of symptoms. A meta-analysis included four clinical trials including the trial described above of the effects of elderberry supplementation on upper respiratory symptoms caused by the common cold or flu in a total of participants age 5 to 59 years [ ].

The analysis showed that elderberry supplementation reduced the duration of upper respiratory symptoms, and the effect was stronger for symptoms of influenza than for those caused by the common cold. A review included the same four trials as well as one that administered an herbal preparation containing both elderberry and Echinacea purpurea [ ].

The results showed that elderberry might help relieve symptoms of the common cold and influenza when taken close to the onset of symptoms and for up to 2 weeks. In contrast, in a clinical trial, 87 male and female participants age 5 years and older with influenza for less than 48 hours took 15 ml 5, mg elderberry extract twice daily for ages 5 to 12 years and four times daily for ages 13 and older or placebo for 5 days [ ].

Elderberry had no effect on the duration or severity of illness. A systematic review of five clinical trials of elderberry to treat viral respiratory illnesses found beneficial effects on some, but not all, outcomes [ ].

The results showed that elderberry supplementation for 2 to 16 days might reduce the severity and duration of the common cold and the duration of flu but does not appear to reduce the risk of the common cold.

However, the authors noted that the studies were small, heterogeneous, and of poor quality. Elderberry flowers and ripe fruit appear to be safe for consumption. However, the bark, leaves, seeds, and raw or unripe fruit of S. nigra contain a cyanogenic glycoside that is potentially toxic and can cause nausea, vomiting, diarrhea, dehydration due to diuresis, and cyanide poisoning [ , , ].

The heat from cooking destroys this toxin, so cooked elderberry fruit and properly processed commercial products do not pose this safety concern [ 3 , , , , ]. Elderberry might affect insulin and glucose metabolism, so according to experts, people with diabetes should use it with caution [ ].

The safety of elderberry during pregnancy is not known, so experts recommend against the use of elderberry supplements by people who are pregnant [ , ]. Recent analyses suggest that some elderberry supplements are highly diluted or have been adulterated with a cheaper ingredient, such as black rice extract, instead of elderberry [ , ].

Due to its potential immunostimulatory activity, elderberry might reduce the effectiveness of immunosuppressant medications [ ]. For information on elderberry and COVID, please see the ODS health professional fact sheet, Dietary Supplements in the Time of COVID Garlic Allium sativum is a vegetable with a long history of culinary use.

Garlic is also available as a dietary supplement in softgel, capsule, tablet, and liquid forms [ ]. Researchers have studied garlic mainly to determine whether it lowers blood pressure and cholesterol levels, but it might also have antiviral properties [ 32 , ].

These properties are often attributed to two compounds in garlic—allicin and ajoen [ ]. Garlic might also have antimicrobial and antifungal activity [ ]. Some dietary supplements contain aged garlic extract, prepared from sliced garlic that is soaked in an aqueous ethanol solution for up to 20 months.

The extract is then filtered and concentrated [ , ]. Aged garlic extract contains compounds, such as lectins, fructo-oligosaccharide, and N-alpha-fructosyl arginine, that might affect immune cell function [ ].

It also contains S-allyl-L-cysteine and other compounds that might have antioxidant effects and reduce some inflammatory markers [ , ]. Only a few clinical trials have examined whether garlic supplements help prevent or treat the common cold or influenza, and results are inconclusive.

One trial included healthy men and women mean age 26 years who took 2. After 45 days, the researchers took blood samples from the participants and cultured the natural killer cells and gamma delta T cells.

The natural killer cells and gamma delta T cells from participants who took the extract had a higher proliferation rate than those from participants who took placebo. After 90 days, the number of illnesses colds and influenza did not differ between groups, nor did the average number of symptoms per illness.

However, participants who took aged garlic extract reported a smaller total number of symptoms during the study. Results were more positive in another trial, in which men and women mean age 53 years took one capsule of a garlic supplement dose not specified or placebo daily for 12 weeks between November and February [ ].

Participants who took garlic had fewer colds 24 among the full study population during the study than those who took placebo 65 colds. In addition, colds lasted an average of only 1. Garlic is safely consumed worldwide as a culinary ingredient [ ], and garlic and its derivatives are generally recognized as safe, according to the U.

Food and Drug Administration FDA [ ]. The adverse effects of garlic dietary supplements are minor and include bad breath, body odor, and skin rash [ 32 , , ]. Garlic might interact with medications. For example, garlic might have anticoagulant effects, so it might interact with warfarin Coumadin and similar medications [ , , ].

However, the findings from reported case studies on this interaction are inconclusive [ ]. Garlic might also reduce blood pressure, so it might interact with antihypertensive medications [ ]. Ginseng is the common name of several species of the genus Panax , most commonly Panax ginseng also called Asian ginseng or Korean ginseng and Panax quinquefolius American ginseng [ , ].

Asian ginseng is endemic to China and Korea, whereas American ginseng is endemic to the United States and Canada [ ]. Triterpene glycosides, also known as ginsenosides, are some of the main purported active constituents of ginseng [ , ]. Although ginseng contains numerous ginsenosides, research has focused on the Rb1 ginsenoside and compound K, a bioactive substance formed when the intestinal microbiota metabolize ginsenosides [ , ].

Animal and laboratory studies suggest that ginseng stimulates B-lymphocyte proliferation and increases production of some interleukins and interferon-gamma [ ]; these cytokines affect immune activation and modulation [ 1 ]. Ginseng might also inhibit virus replication and have anti-inflammatory activity.

However, whether ginseng has a clinically meaningful effect on immune function in humans is not clear [ , ]. Another botanical, eleuthero Eleutherococus senticosus , is sometimes confused with true ginseng.

Eleuthero used to be called Siberian ginseng, but it comes from the Eleutherococcus genus of plants, not the Panax genus, and it does not contain ginsenosides [ ]. Several clinical trials have examined whether ginseng helps prevent upper respiratory tract infections, such as the common cold and influenza.

Although the evidence is limited, results from these trials suggest that ginseng might help reduce the risk of developing colds and other respiratory tract infections.

However, its effects on symptom severity and duration are unclear. In one clinical trial, healthy men and women age 30 to 70 years who had not received an influenza vaccine in the previous 6 months took 1 g Panax ginseng extract three times daily or placebo for 12 weeks [ ].

Participants taking ginseng were less likely to develop an acute respiratory infection during the study period. However, for study participants who did develop an infection, symptom duration and severity did not differ between groups.

A few clinical trials have examined the effects of CVT-E COLD-fX , a patented ginseng extract that contains mg Panax quinquefolius in each capsule. One of these trials included men and women age 18 to 65 years with a history of at least two colds during the previous year who had not received an influenza vaccine in the past 6 months [ ].

Participants took either two capsules per day of Cold-fX for a daily dose of mg ginseng or placebo for 4 months starting in November. Participants who took ginseng developed fewer self-reported colds mean 0.

In addition, ginseng reduced the total number of days with cold symptoms from a mean of A systematic review and meta-analysis of ginseng to prevent or treat acute upper respiratory tract infections included 10 clinical trials of Panax ginseng or Panax quinquefolius extracts including those described above in a total of 2, participants [ ].

The authors noted that the risk of bias was high to unclear for most trials and that the limitations of the evidence prevented them from drawing conclusions. Ginseng appears to be safe. Most of its adverse effects, including headache, sleep difficulty, and gastrointestinal symptoms, are minor [ , , ].

However, doses of more than 2. A few case reports of vaginal bleeding and mastalgia breast pain in the s and s from the use of ginseng preparations raised concerns about the safety of ginseng; as a result, some scientists concluded that ginseng has estrogenic effects [ ].

However, one of these case reports involved use of Rumanian ginseng [ ], and whether this was true ginseng is not clear.

In addition, eleuthero was often referred to, incorrectly, as ginseng at that time because it was called Siberian ginseng.

So, it is unclear whether these case reports reflected the effects of true ginseng. Nevertheless, some experts caution that ginseng might not be safe for use during pregnancy [ , , ].

Ginseng might interact with many medications. For example, it might increase the risk of hypoglycemia if taken with antidiabetes medications, increase the risk of adverse effects if taken with stimulants, and reduce the effectiveness of immunosuppressants [ , ].

For information on ginseng and COVID, please see the ODS health professional fact sheet, Dietary Supplements in the Time of COVID Tea Camellia sinensis is a popular beverage around the world that has several purported health benefits.

Tea is usually classified into one of three types—green, black, and oolong—according to the way in which the tea leaves are processed [ ]. Green tea is made from dried and steamed tea leaves, whereas black and oolong teas are made from fermented tea leaves.

Tea extracts are also available as dietary supplements. The purported health effects may vary by the type of tea as well as whether it is consumed as a beverage or dietary supplement. Tea is one of the richest sources of catechins, which are polyphenolic flavonoids, especially epigallocatechin gallate EGCG [ , ].

A typical mL cup of brewed green tea contains 50 to mg of catechins [ ], whereas the same amount of brewed black tea contains about 14 to 88 mg of catechins [ ].

Amounts vary, however, among tea samples and by brewing time. Studies are evaluating the potential health benefits of EGCG and other catechins, including their ability to modulate the immune system and their anti-inflammatory and antimicrobial properties [ , ].

Laboratory studies suggest that catechins might also have antiviral effects against the influenza A and B viruses [ ]. Laboratory research suggests that tea and tea catechins might have antiviral activity. Researchers have therefore examined whether drinking tea or taking supplemental tea catechins affects the risk, duration, and severity of influenza or other respiratory tract infections.

However, evidence from clinical trials is limited and mixed. Studies that found beneficial effects include a clinical trial that examined the effects of catechins and theanine an amino acid in tea on the risk of influenza in male and female health care workers age 21 years or older in Japan [ ].

However, for laboratory-confirmed influenza, the incidence of influenza did not differ between groups. A systematic review and meta-analysis also showed that tea and tea catechins had some beneficial effects on the risk of influenza and other upper respiratory tract infections, although the evidence had some limitations [ ].

The analysis included five prospective cohort studies and clinical trials that administered tea as a dietary supplement or beverage including the trial described above in a total of 1, participants.

Results were also mixed in a clinical trial examining whether drinking mL of a bottled beverage containing mg of catechins for 12 weeks during the winter affected the duration and severity of upper respiratory tract infections in healthy Japanese men and women mean age Catechins reduced the duration and severity of a runny nose, nasal congestion, and headache but did not affect other symptoms, including sore throat, cough, and fever.

Drinking moderate amounts of tea is safe. Green tea extract causes mostly mild to moderate adverse effects, including nausea, constipation, abdominal discomfort, and increased blood pressure [ ]. However, some green tea extracts might cause liver damage, especially when taken on an empty stomach [ , ].

In addition, at least 50 case reports since have linked consumption of green tea extracts, primarily ethanolic extracts of green tea, with liver damage [ ].

In a systematic review of the safety of green tea products, the U. Pharmacopeia USP evaluated 75 case reports of liver damage and animal pharmacological and toxicological information [ ]. On the basis of the 35 case reports associated with supplements containing only green tea extract, the USP concluded that the consumption of green tea products definitely caused four cases of liver damage, probably or was highly likely to have caused 25 cases, and possibly caused five cases.

The USP notes that problems are more likely when green tea extract is taken on an empty stomach and, therefore, advises taking green tea extracts with food to minimize the risk of liver damage [ , ].

In addition, tea contains caffeine, which can cause sleep disturbances and feelings of nervousness, jitteriness, and shakiness [ ]. These levels do not apply to people who are pregnant and may need to limit caffeine consumption further [ ].

Tea and its constituents might interact with certain medications. For example, green tea extract decreases plasma levels of atorvastatin, a statin medication [ ]. Glutamine is an amino acid that is present in a wide variety of foods that contain protein, including beef, fish, poultry, soy and other beans, eggs, rice, corn and other grains, and milk and other dairy products [ ].

The body also produces glutamine endogenously. In normal conditions, the body can synthesize adequate amounts of glutamine to meet metabolic needs, so glutamine is not classified as an essential amino acid [ ]. However, under extreme physiological stress, endogenous glutamine synthesis cannot keep up with metabolic need.

Therefore, glutamine is classified as conditionally essential [ ]. In the immune system, glutamine is involved in lymphocyte proliferation and cytokine production as well as macrophage and neutrophil function [ ]. Low glutamine levels are associated with poor immunologic function and an increased risk of mortality in patients in the ICU [ , ].

Many patients who are critically ill or have undergone major surgery have low plasma and muscle glutamine levels [ ]. Results from some studies suggest that glutamine reduces rates of infection and mortality in critically ill patients and reduces hospital length of stay and mortality in patients with burn injuries [ , ].

Clinical studies have administered glutamine both enterally and parenterally. When administered through these routes, glutamine is classified as a drug, not a dietary supplement, in the United States.

Researchers have examined whether glutamine administration affects immune parameters and disease prognosis in critically ill patients. The evidence from these studies is limited and mixed.

For example, a crossover trial examined the effects of enteral nutrition containing glutamine on immune function in moderately ill patients with systemic inflammatory response syndrome from a pulmonary infection in the ICU [ ]. Thirty patients age 30 to 92 years received enteral nutrition containing 30 g added glutamine for 2 days followed by enteral nutrition containing 30 g added calcium caseinate for 2 days or the same formulations but in reverse order.

A 1-day washout period with standard enteral nutrition separated each treatment period. Glutamine administration resulted in higher lymphocyte counts than calcium caseinate administration, suggesting enhanced immune function, but did not affect interleukin levels.

Results from clinical trials in patients with critical illness have also been mixed. One trial in the United Kingdom included 84 men and women mean age 65 to 66 years in the ICU [ ]. Patients received a standard parenteral formulation with or without 25 g added glutamine per day.

Treatment duration was not specified, but administration continued until death or as long as clinically required.

Patients who received the formulation with added glutamine had a lower risk of death during the subsequent 6 months than those who received the standard formulation.

In another clinical trial in Scotland, critically ill men and women mean age 63 to 65 years in the ICU received one of four parenteral treatments daily: standard formulation, standard formulation containing Glutamine did not affect the risk of new infections during the 14 days after randomization or mortality rates in the ICU or during the subsequent 6 months.

It also had no effect on ICU or hospital length of stay, need for antibiotics, or rates of organ failure. Findings from a Cochrane Review suggest that glutamine may have beneficial effects on some but not all outcomes in patients who have critical illness or are recovering from major surgery.

This review examined the effects of glutamine administration on various outcomes, including rates of infection and mortality, in adults who were critically ill or had undergone major surgery, such as abdominal or thoracic surgery [ ].