Circadian rhythm shift work -
Many other functions of the body — including temperature, digestion, heart rate and blood pressure — fluctuate through the day, tuned by the activity of the circadian clock. This changing rate of activity over each hour period is known as the circadian rhythm.
A person who works nights, or starts their working day before 6am, is running counter to their circadian rhythm. This may put them at risk of health problems. Research findings are beginning to show that shiftwork can be hazardous to your health. An important body function, which follows the circadian rhythm, is the internal body temperature.
This temperature increases through the day. It reaches the lower level in the early hours of the morning and reaches the maximum level late in the afternoon. The tendency to fall asleep and stay asleep occurs during the decreasing phase of the temperature circadian rhythm between midnight and 4am.
As the body temperature rises, it is more difficult to stay asleep. This is one of the reasons why night workers who try to fall asleep at 8am find it very difficult and also find it difficult to remain asleep through the day. A person working night shift, which causes disruption to the circadian rhythm, is at greater risk of various disorders, accidents and misfortunes, including:.
Shiftworkers get, on average, two to three hours less sleep than other workers. They often sleep though the day in two split periods, a few hours in the morning and then an hour or so before going to work at night.
Night workers can find it difficult sleeping during the day particularly in Australia. The best rotating shift pattern is still undecided.
For the most people, rotating forward through day, afternoon and night shift is better than backwards night, afternoon then day. The frequency of rotation is also controversial. Some people advocate prolonged rotation, such as two to three weeks.
Others advocate short rotations of two to three days. Both have advantages and disadvantages. It takes about 10 days for the body to adjust to night shift work.
However, it is common for night shift workers to revert to daytime routines for a day or two during days off, which tends to make the circadian rhythm unstable. The amount of hours 8-hour versus hour shifts is also controversial. Another risk to sleep is when a worker on seven hour shifts a fortnight uses their free time for another, almost full-time job.
A proportion of shiftworkers may have marked daytime sleepiness, called Shift Work Sleep Disorder. In certain circumstances, they may be helped by careful use of stimulant therapy, on the advice of their doctor.
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This review will concentrate on shift work in relation to biological rhythms since disturbed rhythms appear to underlie many of the short- and long-term health problems of shift workers [ 12—14 ]. To this end, an introduction to the subject is provided.
Since the pineal hormone melatonin is currently used as the primary output marker of the internal clock as well as its actions as a chronobiotic , the search was then restricted to shift work and circadian and melatonin. This provided references, which together with the author's personal collection formed the basis of this review.
Biological rhythms serve to align our physiological functions with the environment. We are a diurnal species and thus, we normally sleep at night and are active during the daytime. The timing of functions with prominent rhythms such as sleep, sleepiness, metabolism, alertness and performance in a normal environment is such that they are optimal during the most suitable phase of the day Figure 1.
Alertness and performance reach their nadir at night during peak sleep propensity and fatigue [ 13 , 16 , 17 ] and close to the low point of core body temperature and the peak of melatonin secretion. The health problems and increased risk of major disease in long-term shift workers are ascribed largely to working out of phase with the internal biological clock.
It is likely that many perceptions of the detrimental effects of clock disruption or abnormal timing derive from observations in shift workers. Diagrammatic examples of circadian rhythms, from Rajaratnam and Arendt, Lancet [13], by permission. Everything is rhythmic unless proved otherwise [ 18 ].
Biological rhythms of various periodicity are ubiquitous. The frequency displayed varies from fractions of a second for example the firing of neurones to years for example population variations. By far, the most information is available concerning daily rhythms [ 18 , 19 ].
They are either externally imposed, internally generated or more frequently a combination of these two factors. Circadian rhythms serve to temporally programme the daily sequence of metabolic and behavioural changes. By definition, they persist in the absence of time cues such as alternating light and darkness and are coordinated by an internal biological clock pacemaker, oscillator situated in the suprachiasmatic nuclei SCN of the brain hypothalamus [ 20 ].
The basis of circadian rhythm generation is a negative feedback loop of clock gene expression [ 21 , 22 ]. The free-running period is individually variable and is an inherited characteristic. On average, the human endogenous period or tau is about In circadian literature, synchronization means that rhythms display a 24 h period but may not necessarily be in the right phase, for example, abnormally delayed or advanced.
Entrainment means that the rhythms are synchronized with the appropriate phase. When entrained to the 24 h day, a short endogenous tau is associated with morning diurnal preference larks and a long tau with evening preference owls [ 18 ].
Because the circadian clock period is not exactly 24 h, it must be reset regularly phase shifted to maintain a 24 h period. The most important time cue for maintaining a 24 h period is the light dark cycle acting partly via a novel retinal photoreceptor system and a novel photopigment melanopsin circadian photoreception [ 24 ].
Recent evidence indicates that short wavelengths of light — nm, blue have the most powerful resetting effects [ 25 ]. Blind people with no conscious or unconscious light perception frequently display free-running rhythms, underlining the importance of light. Specific manipulation of food timing in animals influences a so-called food entrainable oscillator, which is independent of the SCN [ 26 ].
The content of meals in humans may also have a minor influence. The circadian response change in timing or phase shift to light exposure, and indeed to other time cues, is dependent on the strength and timing of the stimulus. The central clock adapts slowly, and with considerable individual variability, to a rapid shift in work time or time zone.
After a time zone change, the average rate often approximates to 1 h of adaptive shift per day. After an abrupt shift in work time, the change is very variable as discussed later [ 29—31 ]. During the process of adaptation, endogenous rhythms are out of phase with the external environment external desynchronization.
They may also be out phase with each other, i. assume a transitory abnormal phase relationship internal desynchronization. Time cues or zeitgebers are all important in controlling the circadian response to such changes.
During a period of desynchrony, for example, a single night of night shift in a sequence of days, workers are attempting to sleep at a time of maximum alertness and to work at the nadir of alertness and performance.
If adaptation of the clock to a new work schedule occurs, the problems of desynchrony resolve [ 32—35 ]. From Paul et al. Many of the genes concerned with circadian rhythm generation in mammals and other species have now been identified, e.
CLOCK, PER1, PER2, PER3, TIM, CRY1, CRY2, BMAL1, REV-ERBALPHA. The mechanism is similar in all species investigated and substantial homology exists between, for example, Drosophila and mammals.
Oscillation of clock genes also occurs in peripheral structures, and in general, they are considered to be coordinated through SCN activity. However, it is possible to shift the timing of some peripheral oscillations for example, in the liver by timed feeding , independently of the SCN [ 36 ].
Investigation of polymorphisms in human clock genes in relation to occupational health and disease is in its infancy. Some polymorphisms have been identified and associations are emerging with phenotypic characteristics such as diurnal preference larks—owls , intrinsic period, vulnerability to disease and response to sleep deprivation [ 37—39 ].
The circadian clock influences hormones, behaviour, cognitive function, metabolism, cell proliferation, apoptosis and responses to genotoxic stress [ 22 ]. There is new strong evidence concerning the importance of circadian control for health in that disruption of circadian clock gene expression can lead to increased incidence or progression of cancer in animals [ 22 , 40 ].
Some examples of human rhythms in disease processes include night time asthma, early morning increases in blood pressure, death rate from cardiovascular disease and stroke, disrupted menstrual cycles, abnormal cortisol rhythm in Cushing's syndrome, sleep disorders for example delayed sleep phase syndrome, advanced sleep phase syndrome, non h sleep wake cycles especially in the blind , some psychiatric disorders.
Numerous aspects of human biochemistry show rhythmicity, even urinary creatinine. Thus diagnostic tests should be aware of these rhythms. Measurement of a given rhythmic variable in someone who has just crossed several time zones, or worked a series of night shifts, can give false-negative or false-positive results.
Moreover, many drugs have a rhythmic variation in both pharmacokinetics and efficacy chronopharmacology. Melatonin N -acetylmethoxytryptamine in an indolic hormone whose principal physiological function is to provide a humoral time cue for the organization of seasonal and circadian rhythms [ 41 ].
In animals which depend on day length to time their seasonal physiology, the length of melatonin secretion signals the length of the night. In specific circumstances, humans may also show changes in the duration of secretion [ 41 ]. There are several phase response curves to melatonin with slight differences, which can be used to predict the chosen timing in order to hasten a circadian phase shift.
This is important in a shift work context given that a number of attempts have been made to treat shift workers with melatonin with variable results. Light of sufficient intensity and spectral composition will suppress melatonin production at night [ 41 , 43 ].
Suppression is detectable at 30—50 lux and maximum from around — lux. This suppression is associated with rapidly increased alertness and core body temperature, although causal relationships are not clear.
It is important in a shift work context as light suppression of melatonin has been hypothesized to be detrimental to health [ 44 ]. A night shift worker whose circadian clock is in day mode, or unadapted, will secrete melatonin during work hours.
Similarly, a worker who has adapted their clock to night shift will secrete melatonin during the day and on return to day shift or rest days will secrete melatonin during the hours of natural daylight. Actual personal light exposure during night shift work has rarely been measured, examples of personal light exposure on North Sea oil rigs are shown in [ 45 ].
Shifts in the timing of melatonin are considered to represent changes in timing of the central clock. Measurement of melatonin in plasma, saliva or its urinary metabolite 6-sulphatoxymelatonin [ 43 ] provides the best peripheral measure of central clock timing Figure 3.
Other marker rhythms such as core body temperature and cortisol are more subject to so-called masking, whereby an internal or external influence distorts the rhythm. For example, exercise and food strongly influence core temperature and stress modifies the cortisol rhythm.
The most reliable results regarding circadian status in shift work have been obtained with melatonin measures and this review will concentrate on melatonin-derived information.
Characteristics of the melatonin rhythm used to define timing of the internal clock. From [ 43 ] by permission. Also for the purposes of this review, the assumption is made, based on controlled laboratory experiments, that when sleep is taken during the period of peak melatonin secretion and thus, in theory, the nadir of alertness, performance and core body temperature , it is optimized.
In night shift conditions, if peak melatonin secretion is shifted to occur during day sleep, it is presumed that adaptation to night shift has occurred.
The most numerically important shift work conditions, at least in the UK, are irregular night shifts sometimes nights and sometimes days and rotating schedules information from the Office of National Statistics Box 1.
Examples of rotations include 3 days early shift e. These common schedules do not allow the internal clock to adapt fully to night shift since there is substantial inertia in the circadian system. After abrupt large changes in time cues, the daily shifts in circadian timing rarely exceed 1—1.
Exposure to morning light in the travel home window after night shift is at a time that opposes a delay shift of the clock to adapt Figure 2 , and daytime social cues counter circadian adaptation.
Data from field studies indicate that the greater the morning light exposure the less circadian adaptation is seen [ 48 ]. In temperate latitudes natural bright light will be more prevalent in summer in the early morning, and any shift of the circadian system during night shift will in theory be countered more strongly than in winter.
Partial shifts in circadian timing can be seen in short-term night shift work, and a relationship to the timing of light exposure is present, either delays or advances, in relation to the light phase response curve [ 29 , 49 , 50 ].
Natural light exposure, the most powerful influence, evidently depends on the shift timing. Also important is the diurnal preference of the subjects [ 29 ]. Evening preference people are reported, as might be expected, to have a greater tendency to delay and morning people to advance [ 29 , 47 ].
Most permanent or long-term night shift workers with exceptions, see below do not adapt their circadian system to the imposed work schedule. This may depend on the ability to maintain night activity and day sleep on days off as well as other factors such as diurnal preference.
However, there is a paucity of data and further research is needed. Thus, the vast majority of shift workers will be working during their circadian nadir and trying to sleep during periods of maximum alertness. The curtailment of sleep when taken during the day in shift workers is well documented and is a cause of sleep deprivation.
Some examples of short sleep are shown in Table 1. Sleep restriction has also been associated with alterations of neuroendocrine control of appetite [ 57—60 ]. Changing from day to night shift often implies a period of 20—24 h without sleep. The decrements in performance during the latter part of this sleep deprivation may be equivalent to an illegal level of alcohol in the blood [ 16 ].
Accidents following a combination of sleep deprivation and working during the circadian nadir in performance and the maximum sleep propensity have led to litigation against individuals and employers [ 13 ].
It is considered that fatigue may be a more important cause of transport accidents than alcohol Figure 4.
Comparison of the effect of blood alcohol concentration BAC and hours of wakefulness on task performance. Higher scores indicate better performance. The decrement in mean performance at blood alcohol concentrations of 0.
From Rajaratnam and Arendt [13] after Dawson and Reid [16] by permission. A Effect of blood alcohol on task performance. The dotted horizontal line is the mean performance at a blood alcohol concentration of 0.
B Performance is likely to be affected by circadian factors and sleep debt, thereby accounting for the recovery in performance after 27 h of wakefulness about h in this experiment.
The circadian system regulates metabolism [ 61 ] and increasing evidence relates circadian desynchrony to disorders such as metabolic syndrome insulin resistance, high blood pressure, central obesity, decreased high density lipoprotein HDL cholesterol, elevated triglycerides triacylglycerol, TAG and cardiovascular disease [ 59 ].
For example, eating a standard meal at night biological night leads to high blood lipid TAG and evidence for insulin resistance, compared to the same meal taken during the day [ 62 , 63 ]. Interestingly, there is some evidence that men are more susceptible to these metabolic abnormalities than women.
TAG is an independent risk factor for development of heart disease. This may provide at least a partial explanation for the increased risk of heart disease in shift workers.
In large surveys, shift workers have higher TAG levels as well as higher total cholesterol than the general population [ 11 , 64 ]. There are associations between polymorphisms in the gene CLOCK , obesity and the metabolic syndrome in man, and mice bearing a particular mutation of the gene CLOCK develop metabolic syndrome and obesity [ 65 , 66 ].
Some exceptions to the general rule that shift workers do not fully adapt to night shift are found in isolated environments. On the British Antarctic Base of Halley, 75°S, each base member does a week of night shift — h, fire watch at a time, in rotation with other personnel.
The vast majority of people shift their circadian system, assessed by aMT6s rhythms in urine, by up to 10—12 h to align with the new work schedule, within a week [ 67 , 68 ]. Thus, the peak of melatonin production occurs within the daytime sleep period—an important condition for sleep duration, latency and quality.
This is thought to be due to the lack of social and family obligations, no requirement to return home in natural light and in winter when the sun does not rise for 3 months, a lack of conflicting light exposure.
In these circumstances, it is apparent that owls adapt by delay faster than larks [ 69 ]. Problems occur when endeavouring to adapt back to day work particularly in winter.
Realignment of the circadian system can take weeks and some people will free-run for a time. These observations in Antarctica prompted studies in somewhat similar circumstances on North Sea oil rigs. Work schedules vary but tours of duty usually last for 2—3 weeks in a socially isolated environment at high latitudes.
Interestingly, a — h schedule is less conducive to circadian adaptation, possibly due to early morning light exposure after work especially in summer [ 72 ]. Sleep is worse during this shift than the — h shift. Seven night shifts — h followed by 7 day shifts — h leads in most people to adaptation to nights but with a very mixed response to the following days [ 30 , 73 ] Figure 5.
Some people delay, some advance and many show little readaptation to days during the first week. The response is partly predictable from the initial circadian phase position: delayed, intermediate or advanced.
Other schedules such as a 7 day, — h day shift followed by a 7 day — h night shift show partial or no adaptation to night shift which is dependent on season [ 71 ]. Again, this can be attributed to light exposure countering adaptation.
Progression of the individual timing of the melatonin rhythm by urinary aMT6s , during a week of nights — h followed by a week of days — h in 11 individuals working on a North Sea oil rig. Most shift their timing such that at the end of nights the peak of melatonin is during the daytime sleep and thus, they are adapted.
The subsequent response to a change to day work is highly variable. From [ 30 ] by permission. Such circumstances, when workers show different circadian timings according to whether or not they have adapted to nights, have allowed field assessments of the metabolic consequences of a night shift meal.
As with controlled laboratory experiments, elevated TAG, low density lipoprotein LDL cholesterol and evidence of insulin resistance were found when unadapted [ 45 ].
These sequelae resolved when adaptation had occurred. Special cases of shift working are seen in marine watchkeeping systems. There are very few data relating to melatonin rhythms; however, a study in submarines has shown evidence that crew can free run while working an 18 h day, submerged for long periods [ 74 ].
Circadian adaptation was studied in crew working 4 h on and 8 h off on fixed or rotating schedules on a British Antarctic Survey ship travelling from the UK to 75°S. They showed evidence of partial circadian adaptation to the — h, — h fixed watch but not to weekly rotating watches [ 54 ].
It is not the purpose of this review to evaluate the epidemiological evidence for increased risk of disease in shift work; this can be found elsewhere. It is generally accepted that there is an increased risk of heart disease and some contributory factors related to the biological clock have been discussed above.
A possible significant association was identified between female breast cancer and shift work some time ago [ 75 ]. This is potentially a major problem since estimates from the Spring wave of the Labour Force survey suggest that an estimated 1.
In , the World Health Organization WHO International Agency for Research on Cancer, IARC published a brief report in the Lancet of an expert meeting on whether or not shift work was associated with an increased risk of cancer, particularly breast cancer.
The conclusion was that shift work was a probable carcinogen [ 77 ]. A full monograph is expected from this meeting but has not yet been published.
There are considerable implications arising from this decision and, for example, according to the UK national press in March , the Danish government decided to compensate shift workers who develop breast cancer. Both the UK and Dutch governments also issued publications discussing the evidence and in general decided that further epidemiological evidence and mechanistic data were needed [ 78 , 79 ].
Assuming that the risk assessments are correct, let us consider the possible mechanisms. The most well-known theory concerning cancer and shift work relates to light exposure at night light at night, LAN. Stevens and Davis [ 44 ] hypothesized that the increasing incidence of breast cancer in the developed world was due to light exposure at night.
He further proposed that, since light suppresses melatonin and melatonin has some oncostatic activity in animals, the increase in breast cancer was due to a decrease in melatonin. Numerous questions arise from this proposal, some of which can be addressed.
The WHO IARC expert meeting concluded that there was definite evidence for anti-cancer effects of melatonin in animals and in vitro but little in humans. It should be noted that human in vivo data are sparse.
The data which directly addressed the cause and effect relationship between melatonin and human breast cancer involved maintaining human breast transplants xenografts in rats and assessing short-term markers of cancer with and without circulating endogenous levels of melatonin.
Physiological levels of melatonin were able to reduce or abolish carcinogenic changes in these markers [ 80 ]. This latter study does suggest that endogenous melatonin has anti-proliferative effects working via a membrane receptor. However, not all studies have shown anti-proliferative effects of melatonin in vitro.
Is melatonin suppressed in night shift workers? There is no answer to this question. However, it should be noted that adrenergic beta-receptor blocking drugs such as atenolol and propanolol suppress melatonin and are not known to be carcinogenic [ 41 ]. Moreover, the individual variability in melatonin production is very large indeed and in cross-sectional studies, large numbers of subjects are needed to show this small overall reduction [ 41 ].
More convincing are the effects of general circadian disruption in animals [ 81 ]. Exposure of animals to continuous light increases vulnerability to cancer development [ 82 , 83 ]. Subjecting rodents to forced phase shifts analogous to rotating shift work or frequent time zone change substantially increases proliferation of implanted cancers [ 40 ].
Manipulation of clock gene function likewise has carcinogenic effects [ 14 , 22 , 84 , 85 ] and the circadian clock is considered to be a tumour suppressor. So the case is close to being made for circadian disruption leading to cancer.
The problem is that increasing light at night in short-term shift work leads to improved alertness, performance and possibly metabolism, while no doubt increasing melatonin suppression.
At present, investigations are proceeding on the use of glasses, which can block the short wavelengths most likely to suppress melatonin while hopefully maintaining alertness and performance.
The question arises as to the benefits and disadvantages of aiding or countering adaptation in order to secure the maximum duration of good quality sleep and other health benefits.
In the unusual case of full adaptation, it makes sense to hasten this process and that of readaptation to day work. In short-term night shift, it may be more useful to maintain daytime circadian phase while using strategies such as alerting stimulants caffeine and possibly modafinil , quiet dark sleeping quarters and possibly hypnotics to preserve sleep and performance.
Light of suitable spectral composition and intensity can be used to adjust the timing and probably amplitude of circadian rhythms. The hormone melatonin can also act as a zeitgeber vide supra.
Light treatment during the first half of biological night prior to the melatonin peak will delay circadian rhythms and during the latter half, after the melatonin peak, will advance rhythms Figure 2. Melatonin treatment by contrast advances rhythms in the first half of biological night and delays them in the latter half.
There is no doubt that in controlled laboratory situations, and with good compliance at home, both light and melatonin, separately or in combination, can be used with correct timing to hasten phase shift of the circadian system to align it with the new work—rest schedule [ 32 , 43 , 50 , 86 ].
There are clear benefits for sleep, alertness and performance. In field situations, the results are inconsistent. Very probably this is due to the large individual differences in response to phase shift and in consequence mistiming of the treatment.
However, in studies offshore and in Antarctica, useful results have been reported with timed light treatment [ 67 , 87 ]. The author is only aware of one combined treatment study, which was offshore and with beneficial effects [ 88 ].
It is possible that the most useful application of melatonin to shift workers would be to facilitate sleep or a nap, prior to night shift. It is particularly difficult to sleep in the early evening, and the combination of low-dose melatonin, a dark room and recumbency is very effective at enabling sleep at this time of day [ 56 ].
An alternative approach has been described recently. This is to shift the circadian system, using timed light and melatonin, just to the point where the melatonin peak falls within the sleep period, avoiding large shifts which lead to readaptation problems [ 34 , 89 ].
This strategy appears to provide benefit for sleep, alertness and performance. However, if the timing is wrong, the opposite of the desired result will be produced.
For example, instead of adapting to an 8 h advance in work time by advancing the clock, the system may delay. Avoidance of light at the wrong time is possibly more important than the light treatment itself. Morningness has been related to intolerance to shift work in some studies although not all are consistent.
Mongrain et al. This observation suggests that workers who are extreme morning types should choose their schedules carefully with regard to preserving sleep. One further study addressing a similar question, but different methodology, found an association with sleep homeostasis but did not confirm the effect on neurobehavioural responses [ 91 ].
No doubt more information will be available shortly given the importance of predicting the possible health consequences of shift work. I would like to thank all colleagues, students, volunteers and funding bodies who have provided input, samples and support for our work on biological rhythms over the years.
I would particularly like to mention Mark Midwinter, Jonathan Ross, Jon Lund, Lil Ng, Gavin Francis, Victoria Mottram Antarctic Base doctors , Richard Barnes, Michelle Gibbs and Helen Thorne University of Surrey PhD students who persuaded numerous workers at Halley Base 75°S and on the North Sea oil installations to provide sequential urine samples during their period offshore.
These heroic efforts have provided a dynamic picture of the long-term circadian response to phase shift. Google Scholar.
Rhthm sleep Minerals for muscle recovery can lead to a whole host of Circadiah on the job, including confusion, poor productivity rhyghm accidents. In fact, sleep deprivation Organic energy boosters been linked to Organic energy boosters major historical disasters, such Organic energy boosters Chernobyl and the Exxon oil spill. While many night shift workers turn to caffeine to stay alert, this stimulant only provides temporary symptomatic relief. Instead, the key to staying awake and alert during night shifts is changing your circadian rhythm. So put down that venti latte, and listen up. The circadian rhythm refers to your internal clock, which tells your body when to sleep, wake and eat.Video
NEUROSCIENTIST: 8 HOUR Sleep Is The WORST - Andrew HubermanCircadian rhythm shift work -
Research findings are beginning to show that shiftwork can be hazardous to your health. An important body function, which follows the circadian rhythm, is the internal body temperature.
This temperature increases through the day. It reaches the lower level in the early hours of the morning and reaches the maximum level late in the afternoon. The tendency to fall asleep and stay asleep occurs during the decreasing phase of the temperature circadian rhythm between midnight and 4am.
As the body temperature rises, it is more difficult to stay asleep. This is one of the reasons why night workers who try to fall asleep at 8am find it very difficult and also find it difficult to remain asleep through the day.
A person working night shift, which causes disruption to the circadian rhythm, is at greater risk of various disorders, accidents and misfortunes, including:. Shiftworkers get, on average, two to three hours less sleep than other workers. They often sleep though the day in two split periods, a few hours in the morning and then an hour or so before going to work at night.
Night workers can find it difficult sleeping during the day particularly in Australia. The best rotating shift pattern is still undecided. For the most people, rotating forward through day, afternoon and night shift is better than backwards night, afternoon then day.
The frequency of rotation is also controversial. Some people advocate prolonged rotation, such as two to three weeks. Others advocate short rotations of two to three days. Both have advantages and disadvantages. It takes about 10 days for the body to adjust to night shift work. However, it is common for night shift workers to revert to daytime routines for a day or two during days off, which tends to make the circadian rhythm unstable.
The amount of hours 8-hour versus hour shifts is also controversial. Another risk to sleep is when a worker on seven hour shifts a fortnight uses their free time for another, almost full-time job. A proportion of shiftworkers may have marked daytime sleepiness, called Shift Work Sleep Disorder.
In certain circumstances, they may be helped by careful use of stimulant therapy, on the advice of their doctor.
A study published by the American Association for Cancer Research found that for every 5 years of night shift work, the risk of breast cancer rises by 3. The suppression of melatonin — the hormone responsible for regulating the internal body clock — may play a role.
People need to work through the night for numerous reasons. Finding ways to cope can be the difference between living a healthy existence and being subjected to the many elevated health and safety risks during night shifts.
Some people can work at night without issue, while others experience sleep deprivation and fatigue. This is because humans are designed to sleep at nighttime. The body is controlled by an internal body clock, or circadian pacemaker, located in the suprachiasmatic nucleus SCN of the hypothalamus.
The SCN generates circadian rhythms , which regulate behavioral and physiological processes in the body, including alertness, sleep, temperature control, and hormone production. Circadian rhythms run in hour cycles and are significantly influenced by the natural light and dark cycles.
Many bodily processes that are active in the daytime slow down at night to prepare for sleep. At night, the circadian pacemaker releases the sleep hormone melatonin from the pineal gland, which causes the body to feel less alert and raises the desire to sleep.
Night shifts cause the body to battle against its natural rhythms by trying to be alert when programmed to be sleeping. Similarly, when you go home after a night shift, the cues from your internal body clock and daytime light exposure tell you to be awake and active.
Adults need between 7—9 hours of sleep to function at their best. Working at night involves successfully managing sleep during the day — that is, to keep sleep debt to a minimum — and fatigue during the night. Daytime sleep can be lighter, shorter, and of poorer quality than sleep at night due to light, noise, and temperature.
After the last shift in a block of night shifts, remember that the more days in a row a person has been working through the night, the more sleep debt they will likely have accrued.
Repaying some of the sleep debt as quickly as possible will help individuals recover sooner. Exposure to light triggers chemical events in the circadian pacemaker that affects your sleep and wake cycles.
For example, the body releases melatonin as it gets dark in the evening to instigate drowsiness. By morning light, the body suppresses melatonin and elevates cortisol levels to make the body feel more awake. Research has shown that night-shift workers who were exposed to bright light during their shift and wore sunglasses on the way home to suppress light drifted off to sleep quicker and slept for longer after their shift than people who received no bright light exposure.
Furthermore, another study found that intermittent exposure to bright light is almost as effective as continual exposure. People should beware of exposure to blue light emitted from digital devices, such as a smartphone, tablet, or television, before bed after a night shift. Research suggests that blue light knocks the circadian rhythm off-kilter , which signals to the brain that it is daytime, resulting in poorer sleep quality.
Keeping the bedroom dark will help keep the body in sleep mode until it is time to wake up and begin the day. When the typical daily rhythm is off-balance, so too is metabolism.
Planning meals can help people stay alert during working hours and be more relaxed for sleep. People could try to consider the following:. Accessing the grocery store and adequate facilities to prepare food can be challenging for night workers.
People should be prepared and take food to work to ensure they eat properly and stay alert. What is the circadian rhythm? Am I at a greater risk of cancer if I do shift work?
The short answer is: maybe. Most research has looked at whether shift work increases the risk of breast cancer. Light exposure at night can decrease the amount of melatonin a hormone produced by the brain.
Melatonin may slow tumour development or change the levels of other hormones, like estrogen. Lifestyle risk factors, including smoking , drinking alcohol , an unhealthy diet, lack of exercise and an unhealthy weight, may be a result of shift work.
Phase shift may contribute to cancer due to changes at the cell and tissue level that result from working at unusual times.
It is a built-in biological rhythm, a rough hour cycle Antioxidant supplements for blood pressure regulates shirt physiological processes such as sleeping Circadian rhythm shift work hrythm. The circadian wlrk rises and Circadian rhythm shift work throughout the day Crcadian responds to environmental cues like sunlight. Learn more about how shift work can affect your health and your risk of cancer. The International Agency for Research on Cancer IARC has concluded that shift work working outside the normal workday, often at nighttime probably causes cancer when it affects circadian rhythms our internal clock. This conclusion is based on data from animal studies and a limited amount of research in humans.
We can feel groggy when our Alertness booster schedule is thrown off wrk just a little. So what happens when shift work Circaidan people Minerals for muscle recovery regularly Circasian awake through Minerals for muscle recovery night and sleep during the Circadian rhythm shift work — and Circaian can they protect their health and well-being? So-called shift work disorder mainly strikes rhyth, who work the overnight or early morning shift, or who rotate their shifts, says Eric Zhou, an assistant professor in the Division of Sleep Medicine at Harvard Medical School. It is characterized by significant problems falling and staying asleep, or sleeping when desired. That's because shift work disrupts the body's normal alignment with the hour sleep-wake cycle called the circadian rhythm. But for shift workers, their work hours and sleep hours are misaligned with the natural cues to be awake or asleep," Zhou says. A research review in the Journal of Clinical Sleep Medicine links shift work to higher risks for serious health problems, such as heart attack and diabetes.
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