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Shift Work · Circadian Misalignment
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In one pass Shift work harms the body for one core reason: the brain's master clock, the suprachiasmatic nucleus (SCN), says sleep while you are forced to stay awake, and says wake while you are forced to sleep.
Educational content, not medical advice — consult a clinician.
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Chapter 1
Why shift work harms the body
Shift work harms the body for one core reason: the brain's master clock, the suprachiasmatic nucleus (), says sleep while you are forced to stay awake, and says wake while you are forced to sleep.
The SCN sends its rhythm to the local clocks in organs such as the liver, the heart and the immune system. Night work pulls the central clock and these peripheral clocks apart, a state called internal desynchrony, and metabolism, immunity and hormones all lose their beat. About 20% of workers worldwide do some form of shift work. In 2007 the International Agency for Research on Cancer (IARC) classified shift work that involves circadian disruption as Group 2A, meaning probably carcinogenic; 2A describes how certain the evidence is, not how large the risk is.
Having no choice does not mean you can only grit your teeth: light, meal timing and recovery sleep all reduce the harm. But if you fall asleep suddenly while driving or operating machinery, have lasting chest pain or trouble breathing, or have thoughts of harming yourself, see a doctor immediately.
The SCN sends its rhythm to the local clocks in organs such as the liver, the heart and the immune system. Night work pulls the central clock and these peripheral clocks apart, a state called internal desynchrony, and metabolism, immunity and hormones all lose their beat. About 20% of workers worldwide do some form of shift work. In 2007 the International Agency for Research on Cancer (IARC) classified shift work that involves circadian disruption as Group 2A, meaning probably carcinogenic; 2A describes how certain the evidence is, not how large the risk is.
Having no choice does not mean you can only grit your teeth: light, meal timing and recovery sleep all reduce the harm. But if you fall asleep suddenly while driving or operating machinery, have lasting chest pain or trouble breathing, or have thoughts of harming yourself, see a doctor immediately.
Mechanism · How the central and body clocks pull apart
The is the brain's central clock. Left to itself it runs a cycle of about 24.2 hours, a little longer than a real day. It is reset each day by morning light: a class of light-sensing nerve cells in the retina, the intrinsically photosensitive retinal ganglion cells (ipRGCs), detect blue light, and when the SCN receives their signal it holds back melatonin release from the pineal gland. Without that reset, the SCN drifts by about 12-14 minutes a day. It then sends its rhythm out to the whole body: the liver, kidneys, heart, muscles, immune system and hormone glands each have their own peripheral clock.Shift work, at its core, forces these two layers of clocks to fight. At work you are pushing against the sleep pressure built up over the day (adenosine accumulating in the brain) and against your own melatonin, propped up by caffeine and night-time lighting. After work you are forced to sleep in daylight, while sunlight, noise and social life push melatonin down again. The result is internal desynchrony: the liver's glucose rhythm, immune regulation, the timetable of the stress-hormone axis (the axis), and the appetite hormones ghrelin (hunger) and leptin (fullness) all fall out of step.
It feels like jet lag that never lets you adjust: never enough sleep, light sleep, chaotic appetite, weight gain, mood swings, and slower attention and reactions. Higher accident rates on night work are a biological limit, not an attitude problem. Managing light, fixing a window for meals, short rotations, blue-blocking glasses, short naps and planned use of melatonin (see Melatonin) are levers that reduce harm; they do not make shift work healthy.
Evidence · The long-term toll, system by system
The health cost of long-term shift work shows up in almost every system, and most of it grows with the years. Below is one main line per system, with the type of evidence stated.Cardiovascular: Vetter 2016, published in JAMA, used two Nurses' Health Study cohorts, about 190,000 initially healthy women nurses followed for 24 years. It is an observational study, not a randomized trial. The highest exposure category was ≥10 years of rotating night shifts; the more years of rotating night work, the higher the risk of coronary heart disease, and in the younger of the two cohorts, the longer since a nurse had stopped shift work, the lower her risk. On mechanism, rhythm-driven rises in blood pressure, poorer function of the blood-vessel lining (the endothelium) and chronic inflammation are thought to act together.
Cancer: years of light at night suppress melatonin and disturb clock genes, which is thought to be linked with breast and prostate cancer risk. IARC therefore classified shift work involving circadian disruption as Group 2A, probably carcinogenic to humans (Straif 2007); the grade describes how certain the evidence is, not how large the risk is.
Metabolic: the body handles glucose less well at night to begin with, so eating at night throws blood sugar and fat handling off. In a of observational studies (Gan 2015), shift workers had a 9-46% higher risk of type 2 diabetes: about 9% higher overall, and higher in men and in people on rotating shifts. Long-term night workers also tend to carry more visceral fat (one estimate puts it at about 5-10 kg more, a figure that still lacks a reliable source) and are more likely to develop fatty liver.
Mental and cognitive: chronic short sleep plus misaligned rhythms make depression and anxiety more common and wear down memory and focus, and living out of step with other people carries a social cost. Gut: more reflux, indigestion and irritable bowel, with lower diversity of gut bacteria. Reproductive: women have more menstrual irregularity and preterm birth; men have lower semen quality. Most of this comes from observational studies; these are associations and cannot prove cause on their own.
Accidents: reactions slow down during the body's biological night. The Chernobyl, Exxon Valdez oil-spill and Bhopal gas disasters all happened on night shifts and are often cited, but a single accident cannot show a cause. Accident rates say more: one report puts night-shift medical error rates at about 1.6 times those of day shifts, and motor-vehicle crashes are also more common.
Even on permanent nights with no rotation, daylight after work and family life pull the clock back toward day. Folkard 2008 reviewed six studies that measured the melatonin rhythm: among permanent night workers, fewer than 3% adjusted completely, and fewer than one in four adjusted enough to benefit. The exceptions usually cited are extreme settings such as offshore drilling platforms or the Arctic winter, where there is no strong light on the way home. Most shift workers have no choice, so this is about reducing harm, not about telling you to change jobs: short, forward (clockwise) rotations are often more workable than permanent nights or irregular slow rotations, combined with light, meal timing and recovery sleep.
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Chapter 2
How far light can shift your clock
How far light can move your body clock depends on when in the clock's cycle the light arrives. This rule is called the phase response curve (PRC) for light. Morning light in the first 0-3 h after waking pushes the clock earlier, so you fall asleep and wake earlier the next day; evening light in the 0-4 h before sleep pushes it later, so you fall asleep and wake later.
Pushing later is easier than pushing earlier: the 's own cycle is about 24.2 h, a little longer than a day, so it naturally leans late. Lewy 1998 found that the response curve for melatonin runs about 12 h out of step with the one for light, so a small dose of melatonin taken 4-6 h before your target bedtime (see Melatonin) can add an extra push earlier.
If you want to adapt to night work, the principle is: bright light on shift as if it were daytime, block the morning light on the way home, and sleep in a fully dark room.
Pushing later is easier than pushing earlier: the 's own cycle is about 24.2 h, a little longer than a day, so it naturally leans late. Lewy 1998 found that the response curve for melatonin runs about 12 h out of step with the one for light, so a small dose of melatonin taken 4-6 h before your target bedtime (see Melatonin) can add an extra push earlier.
If you want to adapt to night work, the principle is: bright light on shift as if it were daytime, block the morning light on the way home, and sleep in a fully dark room.
Mechanism · How far light pushes, and which way to rotate
Light in the middle of the night (the 's true midnight, usually 2-4 am) has a muddled effect: it neither clearly pushes the clock earlier nor clearly pushes it later. The middle of the day (most of the time from about 8 am to 6 pm) is a dead zone, when light has the least effect on the SCN. In most studies, the largest shift a single light exposure can produce is about 1-2 hours per day.Misalignment accumulates: the longer it lasts, the harder the reset. The acute jet lag of one All-Nighter does much less harm than the chronic misalignment of consecutive night shifts. To adapt as well as you can, group night shifts together and group days off together, rather than switching every other day.
On the direction and speed of rotation, experts generally hold that slow rotation (a week of days, a week of evenings, a week of nights, in a loop) is the worst: the SCN is always chasing and never catches up. Fast rotation (2-3 days per block, moving forward from days to evenings to nights) is somewhat better, because the SCN does not try to adapt fully, so less misalignment builds up. Permanent nights may keep phase steadier for some people, at a large social cost. Rotating forward (clockwise) is more workable, again because the SCN's cycle is a little longer than 24 hours. It is the same reason that flying from the US West Coast to the East Coast (which needs an earlier clock) causes worse jet lag than flying east to west.
When the midpoint of your sleep differs by more than 2 hours between workdays and days off, that is clear social jet lag, roughly like taking a transcontinental flight every week; in observational studies it is associated with obesity, cardiovascular disease and depression. Keep weekend late nights within 1 hour; the most important part is getting up at about the same time on days off. How melatonin (see Melatonin) pairs with light depends on whether you want to push the clock earlier or later.
In practice · A fixed night shift, hour by hour
Below are common ways to adapt to a fixed night shift (10 pm-6 am), laid out by the clock. Most come from laboratory studies and expert advice; not every step has been tested in a trial.Before work (3-6 pm): after you get up, avoid long stretches in the sun, and wear sunglasses outdoors; use moderate indoor light rather than strong direct daylight. Start of shift (10 pm): use bright light at work (5000-10,000 lux) to simulate your new daytime. Keep the light bright through the shift. Caffeine is fine (see Caffeine + L-Theanine), but stop at least 6 hours before you plan to sleep after the shift; on an 8-hour night shift that means drinking it only in the first half. Drink a glass of water and take a short walk every 2-3 hours. Avoid large meals, especially between 1 and 4 am: this is when the body handles glucose worst, so the same meal raises blood sugar more, and the gut is more easily upset.
End of shift (6 am): wear blue-blocking sunglasses on the commute and skip a big breakfast (it tells the "it is morning"). Home (7 am): close blackout curtains and keep the room cool and quiet; if you use melatonin (see Melatonin), a small dose is enough; its main job is to tell the SCN it is night, and its effect on sleep varies from person to person; aim for 8 hours of unbroken sleep. Getting up (3 pm): do not walk straight out into the sun; wake up gradually indoors, then eat the first meal of your day.
If you have several days off in a row, you can ease back toward a daytime rhythm (morning sunlight, earlier bed and earlier rising). If you have only 1 day off, do not switch; hold your night-shift phase for the next shift. Blue-blocking glasses on the commute home are the key step: morning sunlight is 3000-10,000 lux, far brighter than indoor lighting, and the light along that commute alone is enough to pull your body clock toward day. Blackout curtains are the best-value investment for night work. A nap of 30-90 minutes before the shift reduces fatigue at work; a 20-minute nap between 3 and 5 am can restore alertness, and it is usually too short to reach deep sleep (which tends to arrive about 30 minutes after falling asleep). Do not nap longer than 30 minutes on shift, or you will drop into deep sleep and wake up groggier.
Chapter 3
When to eat on night shifts
The body handles glucose less well at night to begin with. In a laboratory study (Scheer 2009), healthy adults ate and slept at times shifted about half a day from their usual schedule: the same meals raised blood sugar about 6% more, even though they were releasing more insulin. Years of night work combined with eating at night are associated with a higher risk of type 2 diabetes and metabolic syndrome.
So the rule for eating on night shifts is: put the main meal in the part of the day your body clock still treats as daytime, which on a fixed night shift means before work; try not to eat between 1 and 4 am, and if you are truly hungry, have a little protein with vegetables.
So the rule for eating on night shifts is: put the main meal in the part of the day your body clock still treats as daytime, which on a fixed night shift means before work; try not to eat between 1 and 4 am, and if you are truly hungry, have a little protein with vegetables.
In practice · Meal timing, weight and medicines on nights
The same calories eaten at different times lead to noticeably different metabolic results. The Scheer 2009 study was a small laboratory study that created misalignment on purpose, so it shows the direction of the effect; the step to "years of night work plus night meals speed up type 2 diabetes and metabolic syndrome" comes from observational studies.Put the main meal in the part of the day the still considers daytime. On a fixed night shift, that means before work (6-8 pm, which is your breakfast and lunch). On rotating shifts, follow the daytime of that working day. Try not to eat between 1 and 4 am (the SCN's true midnight). If you have to eat then (low blood sugar, too sleepy to function), have a little protein with vegetables and avoid carbohydrates with a high glycemic index ().
Time-restricted eating (, fitting a day's eating into a fixed number of hours): most studies use an 8-12 hour window aligned with the person's own day. The night-shift version: your day may run from 6 pm to 8 am, so the eating window can sit at 6 pm-2 am (8 hours), with nothing after 2 am until the next morning. Caffeine (see Caffeine + L-Theanine) also needs timing, because it affects the signal the SCN receives: stop at least 6 hours before you plan to sleep, which on a 10 pm to 6 am shift puts the cut-off around 1 am.
Losing weight on nights is harder. Laboratory studies suggest that misalignment may lower a day's energy expenditure slightly and make fat more likely to settle around the organs. It can be done, but it has to be stricter: a fixed eating window, enough protein, strength training and good sleep. An extreme low-calorie diet is not recommended: on mechanism, it may further disturb a stress-hormone axis that is already out of rhythm, and the rebound can be harder. Shift workers with diabetes, high blood pressure or fatty liver should pay extra attention to meal timing, check (HbA1c) and blood pressure every 3-6 months, and discuss the timing of their medicines on night shifts with a doctor (some insulins and blood-pressure drugs need adjusting). drugs (such as semaglutide) have barely been studied in shift workers specifically; whether and how to use them is a question for your doctor.
Night-shift colleagues tending to gain weight is neither coincidence nor weak willpower: meals at the wrong time, too little sleep, ghrelin and leptin out of step, a misaligned cortisol rhythm, fat that prefers to settle around the organs, and long hours sitting all pile up. Weekend binges may be worse than off-schedule eating on workdays, because, on mechanism, they add yet another clock switch. If you want to relax at the weekend, eat a bit less and do not stay up all night. The worst pattern is a weekend All-Nighter followed by a big meal in the early morning, which throws off the SCN and metabolism at the same time.
Chapter 4
Using melatonin and caffeine
On shift work, melatonin is not a sleeping pill. It sends the brain's master clock (the ) a signal that says "it is night now". On a fixed night shift, the usual approach is to take a small dose of melatonin (see Melatonin) on the way home, before daytime sleep; the study results are mixed. Do not take it before driving or operating machinery.
Keep caffeine (see Caffeine + L-Theanine) to the first half of the shift, stopping at least 6 hours before you plan to sleep; use bright light at work and blue-blocking glasses on the way home.
If you are still extremely sleepy in the daytime after enough sleep, snore loudly with pauses in breathing, or have new palpitations or chest pain, stop and see a doctor. If you feel low and have thoughts of harming yourself, get urgent help.
Keep caffeine (see Caffeine + L-Theanine) to the first half of the shift, stopping at least 6 hours before you plan to sleep; use bright light at work and blue-blocking glasses on the way home.
If you are still extremely sleepy in the daytime after enough sleep, snore loudly with pauses in breathing, or have new palpitations or chest pain, stop and see a doctor. If you feel low and have thoughts of harming yourself, get urgent help.
In practice · Timing melatonin, caffeine and light
Fixed night shift: the Sack 2007 review looked at studies of night workers taking melatonin before daytime sleep and found the results mixed: doses ranged from 0.5 to 10 mg and the timing varied, and any better day sleep may simply be its sleep-promoting effect rather than a shift of the body clock. If you want to try it, take a small dose on the way home, before daytime sleep (see Melatonin); larger doses do not work better. In the first days after a shift change, melatonin may help the clock adjust, but the evidence is just as limited; light does most of the work.When not to use it: every day before work (it will make you drowsy on the job); before driving or operating machinery (the leftover effect slows reactions); large doses (the extra is not more effective and is more likely to leave you groggy after waking).
How to use caffeine (see Caffeine + L-Theanine): 100-200 mg 30-60 minutes after the shift starts (about one cup of coffee or two cups of green tea); if needed, a small cup around 1 am, and that is the last one: leave at least 6 hours before you sleep after the shift, since Drake 2013 found that caffeine taken 6 hours before bed still disrupted sleep. People break caffeine down at different speeds, but no trial supports adjusting the cut-off for that. Keep the total at or under 400 mg, which is the daily upper limit for healthy adults, so one shift should not exceed it either. A preventive nap of 30-60 minutes before work helps. A so-called caffeine nap means drinking coffee and then sleeping for 20 minutes right away, so you wake just as the caffeine takes effect and the post-nap grogginess has passed (Hayashi 2003 and other studies).
A 5000-10,000 lux light box: use it for 30-60 minutes at the start of the shift and keep the workplace bright; this is closer to the source of the signal than any caffeine or supplement. Wear blue-blocking glasses on the commute home to stop blue light from activating the ipRGCs (the retinal cells that sense light and report to the ); there is no need to wear them all night at work, because then you need to be alert, and blue light is helping you.
Night-shift red flags, stop and see a doctor: extreme daytime sleepiness even after 7-8 hours of sleep; sleep onset under 5 minutes plus sleep paralysis plus hallucinations (narcolepsy screen); loud snoring plus apneas plus hypertension (sleep apnea; shift workers are high-risk); depression plus thoughts of self-harm (urgent); new palpitations or chest pain (cardiovascular evaluation).
The cost is real; do not pretend that adapting means you are fine. Most of the cost grows with the dose: fewer night shifts are better than more, and short-term is better than long-term. Light, melatonin, meal timing, blue-blocking glasses and good sleep can remove part of the harm, not all of it. If you can, cut down on night shifts over the long run; the cost grows with age. Have a yearly check-up that watches blood pressure, (HbA1c) and blood lipids, and includes screening for sleep apnea. Nothing makes shift work healthy, and anyone who says otherwise is marketing; what you can do is reduce the harm and know when to ask for help.
In practice · Your first four months on shifts
To read further: how caffeine acts on adenosine, and why some people clear it fast and others slowly, is covered under caffeine (see Caffeine + L-Theanine); why about 0.3 mg of melatonin already saturates its receptors, what the dose curve looks like, and how to read the Lewy 1998 phase response curve are covered under melatonin (see Melatonin). Cognitive behavioral therapy for insomnia (), metabolic syndrome (which shift work speeds up), and the evidence on magnesium and ashwagandha for sleep and stress each have their own chapters on the site.If you have just started shift work, your first four months can be set up like this. Month 1: buy blackout curtains, blue-blocking glasses, earplugs and a light box; fix a sleep period that stays the same on days off; set an eating window. Month 2: if you want to try it, add a small dose of melatonin at the end of the shift, set your caffeine cut-off, fix the time of your main meal, and keep a sleep diary with notes on your energy and weight. Month 3: recheck (HbA1c), blood lipids, blood pressure, vitamin D and ; consider whether you need cognitive behavioral therapy for insomnia or a sleep specialist; do strength training 2-3 times a week. Month 4: review which levers helped you most, and plan how to cut the total night hours you work in a year.
Shift work plus a long life plus perfect health is close to impossible. Shift work plus harm reduction, risk monitoring and a decent quality of life is entirely possible. After leaving shift work (moving to days, retiring), part of the damage to the heart, weight and sleep can recover, while cancer and neurodegeneration risk is cumulative. Knowing this is how you avoid being lulled by lines such as "being a night owl is just your personality", and why you need not believe that you will get used to it or that 8 more coffees will do.
Chapter 5
Weekly setup and long-term plans
The will not change its phase just because you need to work, so light, meal timing and recovery sleep need to be managed like the dose of a medicine.
The levers you can actually move are few: a fixed schedule; bright light on shift and blocked light on the way home; big meals in your body clock's daytime; a small dose of melatonin after the shift; a nap before work; and a yearly check of blood sugar, blood lipids and blood pressure. Most of the cost grows with the dose: fewer night shifts are better than more.
Falling asleep while driving or operating equipment, lasting chest pain or trouble breathing, and thoughts of harming yourself all mean seeing a doctor immediately, not waiting for your next check-up.
The levers you can actually move are few: a fixed schedule; bright light on shift and blocked light on the way home; big meals in your body clock's daytime; a small dose of melatonin after the shift; a nap before work; and a yearly check of blood sugar, blood lipids and blood pressure. Most of the cost grows with the dose: fewer night shifts are better than more.
Falling asleep while driving or operating equipment, lasting chest pain or trouble breathing, and thoughts of harming yourself all mean seeing a doctor immediately, not waiting for your next check-up.
In practice · A week-by-week setup, and when to stop
Week 1: first assess your shift load. Is your pattern permanent nights, slow rotation or fast rotation? Do you work fewer than 5, 5-10, or more than 10 night shifts a month? Have you been doing it for under 1 year, 1-5 years, or over 5 years? Then make a symptom list that covers sleep, appetite, weight, mood, sexual function and attention.Weeks 1-2: set up the physical environment: blackout curtains, blue-blocking glasses, a light box, earplugs plus white noise, and temperature control. Weeks 2-4: start the behavioral plan: a fixed wake time (the same on days off); a caffeine cut-off at least 6 hours before you plan to sleep (see Caffeine + L-Theanine); big meals in the 's daytime; if you try melatonin, a small dose after the shift (see Melatonin); and a preventive nap before work. Weeks 4-12: start tracking: a sleep diary, a 1-10 rating of your energy, weight, waist and blood pressure once a month, and (HbA1c) every 3 months.
Red flags, see a doctor immediately: falling asleep while driving or operating equipment (narcolepsy screen, stop high-risk tasks at once); persistent chest pain or shortness of breath; depression plus thoughts of self-harm; loud snoring plus hypertension (evaluate sleep apnea); new-onset prediabetes, strengthen intervention.
In practice · One year, five years, a whole career
Within a year: get the week-by-week levers running smoothly, have a check-up to set a baseline, and, if there is room, discuss the rotation pattern with your employer. Within five years: if you can, reduce your share of night shifts and move toward roles with fewer nights; after 40, cardiovascular and metabolic risk rises faster, so it is worth reassessing your career path. Across a career: in observational studies, people with ≥20 years of shift work have clearly higher health risks; some hold that earlier retirement brings health benefits for shift workers, although direct evidence is thin; and after moving to day work, some studies have seen certain markers improve within 1-3 years, though this research is also limited.If you schedule other people's shifts: short clockwise rotations (2-3 days per block) are usually safer than slow or counter-clockwise rotations; it is wise to cap the cumulative years anyone spends on permanent nights; leave a route back to day shifts for workers over 40; light boxes and blue-blocking glasses at work are not expensive; allow short, safe naps; and run a yearly check-up aimed at shift work.
Modern society needs hospitals, police, emergency services, transport and factories running 24 hours a day. What society owes shift workers is structural harm reduction, not "you will get used to it". What you yourself can actually move are still those few levers. Doing them well is how you spare your future self trouble decades from now.
References · 7
- Straif, K., Baan, R., Grosse, Y., Secretan, B., et al. (2007). Carcinogenicity of shift-work, painting, and fire-fighting. The Lancet Oncology, 8(12), 1065-1066. 10.1016/S1470-2045(07)70373-X
- Lewy, A. J., Bauer, V. K., Ahmed, S., Thomas, K. H., Cutler, N. L., Singer, C. M., Moffit, M. T., & Sack, R. L. (1998). The human phase response curve (PRC) to melatonin is about 12 hours out of phase with the PRC to light. Chronobiology International, 15(1), 71-83. 10.3109/07420529808998671
- Vetter, C., Devore, E. E., Wegrzyn, L. R., Massa, J., Speizer, F. E., Kawachi, I., Rosner, B., Stampfer, M. J., & Schernhammer, E. S. (2016). Association between rotating night shift work and risk of coronary heart disease among women. JAMA, 315(16), 1726-1734. 10.1001/jama.2016.4454
- Scheer, F. A. J. L., Hilton, M. F., Mantzoros, C. S., & Shea, S. A. (2009). Adverse metabolic and cardiovascular consequences of circadian misalignment. Proceedings of the National Academy of Sciences, 106(11), 4453-4458. 10 adults (5 women) in a 10-day laboratory protocol with a recurring 28-h day, so that they ate and slept at all circadian phases; the comparisons are within the same people. When they ate and slept about 12 h out of phase, leptin fell 17%, glucose rose 6% despite 22% higher insulin, the daily cortisol rhythm reversed, mean arterial pressure rose 3% and sleep efficiency fell 20%; 3 of 8 subjects with sufficient data had post-meal glucose in the prediabetic range (abstract, PMID 19255424). 10.1073/pnas.0808180106
- Drake, C., Roehrs, T., Shambroom, J., & Roth, T. (2013). Caffeine effects on sleep taken 0, 3 or 6 hours before going to bed. Journal of Clinical Sleep Medicine, 9(11), 1195-1200. Randomized, double-blind, placebo-controlled Latin-square crossover in 12 healthy normal sleepers: one fixed 400 mg dose of caffeine (the authors call it moderate) at 0, 3 or 6 h before habitual bedtime vs placebo, sleep measured at home by diary and a portable monitor. All three timings disrupted sleep vs placebo (P < 0.05). By the objective monitor, even at 6 h caffeine reduced sleep by more than 1 hour; by diary, the 6-h reduction in total sleep time (41 min) only approached significance (p = 0.08). The authors conclude that substantial caffeine should be avoided for a minimum of 6 hours before bedtime, and that afternoon caffeine should at least be restricted to before 17:00 (abstract, PMID 24235903; full text, PMC3805807). 10.5664/jcsm.3170
- Brzezinski, A., et al. (2005). Effects of exogenous melatonin on sleep: a meta-analysis. Sleep Medicine Reviews, 9(1), 41–50. 17 studies, 284 subjects: melatonin reduced sleep onset latency by 4.0 min (95% CI 2.5-5.4), increased sleep efficiency by 2.2% (0.2-4.2) and total sleep by 12.8 min (2.9-22.8); in the 15 studies of healthy people or people with insomnia only: 3.9 min, 3.1% and 13.7 min (abstract, PMID 15649737). 10.1016/j.smrv.2004.06.004
- Sack, R. L., Auckley, D., Auger, R. R., Carskadon, M. A., Wright, K. P., Jr., Vitiello, M. V., & Zhdanova, I. V. (2007). Circadian rhythm sleep disorders: part I, basic principles, shift work and jet lag disorders. An American Academy of Sleep Medicine review. Sleep, 30(11), 1460-1483. Evidence review for the AASM; treatments fall into prescribed sleep scheduling, circadian phase shifting, and symptomatic hypnotics or stimulants. On melatonin before daytime sleep in night workers (full text, section 6.4.2.2): two shift-work simulation studies and several field studies at 0.5-10 mg, none in workers formally diagnosed with shift work disorder; its conclusion is that the evidence of benefit is mixed, that variable schedules, doses and timing make firm conclusions difficult, and that any improvement in day sleep may be a hypnotic as well as a phase-shifting effect (abstract, PMID 18041480; full text, PMC2082105). 10.1093/sleep/30.11.1460