Body-Clock Problems: Delayed Sleep, Shift Work and Jet Lag

The body clock in brief

Circadian rhythms are physical, mental and behavioral changes over a roughly 24-hour cycle. Light and dark have the biggest influence, but food, stress, activity, social environment and temperature also affect them. [1] The brain's master clock controls melatonin production based on the light your eyes receive. [1] Circadian rhythm sleep-wake disorders are problems falling asleep or waking at the right times, which may be due to shift work or jet lag. [2] See How sleep works for the basics.

Delayed sleep-wake phase disorder (very late sleeper)

People with delayed sleep-wake phase disorder (DSWPD) have trouble falling asleep at usual times and waking in the morning. They typically have difficulty getting to sleep before 2 to 6 a.m. and would prefer to wake between 10 a.m. and 1 p.m. [3] Only a clinician can say whether this applies to you.

What helps: In its insomnia guidance, the NHLBI says a provider may recommend light therapy, sitting daily in front of a light box that produces bright light similar to sunlight, to set and maintain the sleep-wake cycle. [4] Melatonin: the American Academy of Sleep Medicine's weak 2015 recommendation supports specifically timed melatonin, and a 4-week trial of 307 people found melatonin 1 hour before the desired bedtime plus a set bedtime led to falling asleep about 34 minutes earlier; whether benefits outweigh harms remains uncertain. [3] Evidence label: promising but limited. Timing of melatonin matters, so do this with a clinician. See Melatonin.

Advanced sleep-wake phase disorder (very early sleeper)

Proper evidence not found in the sources read for this page that describes advanced sleep-wake phase disorder or its care in plain terms. What the National Institute on Aging does say is that older adults tend to go to bed and wake earlier than they did when younger, which is part of normal aging. [5] If early sleepiness and early waking interfere with your life, ask a clinician.

Shift work and sleep

Shift work that involves night shifts can make people feel sleepy at work and make daytime sleep difficult. [3] Night work and frequent shift changes can disturb the sleep-wake cycle and raise the risk of insomnia. [6]

Strategies suggested by the NHLBI for shift workers:

• Take naps and raise the time available for sleep.


• Keep lights bright at work.


• Limit shift changes so the body clock can adjust.


• Limit caffeine to the first part of the shift.


• Remove sound and light distractions from the bedroom during daytime sleep, for example with light-blocking curtains. [7]

If you still cannot sleep in the day or adapt to the schedule, talk with a doctor about other options. [7] Melatonin evidence for shift workers is mixed: two 2014 reviews were small or inconclusive, with one suggesting about 24 minutes more daytime sleep in low-quality evidence, and a 2022 review of 10 studies suggested it may help. [3][8] Link to Sleep hygiene and see Sleep at different life stages and situations.

Jet lag

Jet lag is when your normal sleep pattern is disturbed after a long flight; it usually improves within a few days as your body adjusts. [9] Symptoms include difficulty sleeping at bedtime and waking, tiredness, trouble staying awake in the day, poor sleep quality, concentration and memory problems, and sometimes indigestion or nausea. [9]

Practical steps from the NHS:

• Before you travel, rest well and consider shifting bedtime toward the destination's time zone. [9]


• On the flight, drink water, stay active, sleep if it is night time at your destination, and limit caffeine and alcohol. [9]


• After arriving, move to the new schedule quickly, go outside in daylight, and avoid daytime sleep. [9]


• For trips of 2 to 3 days, you could keep your home eating and sleeping times. [9]

Melatonin and jet lag. NCCIH says reviews suggest melatonin may help, based on small studies, for example 4 studies of 142 travelers eastward and 2 studies of 90 travelers westward. [3] The NHS does not recommend melatonin tablets for jet lag because of insufficient evidence, and says medicines are not usually needed. [9] Evidence label: mixed. Sleeping tablets can be addictive and are only for short use in severe cases. [9]