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Aircrew Safety & Health – Circadian Rhythm Disruption

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HIAPER research aircraft taking off

Photo courtesy of Julie Haggerty (NCAR)

What you need to know

Circadian rhythm is the internal biological clock that regulates body functions based on our wake/sleep cycle. It can be disrupted by changes in sleep pattern. Aircrew members may experience circadian rhythm disruption (specifically “jet lag”) as they work. Here you can learn more about circadian rhythm disruption, why it occurs, possible health effects, and how crewmembers can reduce the effects of circadian disruption.

Why might aircrew be concerned about circadian rhythm disruption?

Aircrew often travel across time zones and work when others would normally be asleep. This can affect their internal biological clock and disrupt normal sleep patterns which can lead to fatigue, difficulty sleeping, changes in mood, injuries, stomach and intestinal symptoms, and other health problems.

Although travelers who get circadian disruption after a single flight recover after 1-2 weeks, many crewmembers are continually exposed and show evidence of chronic circadian rhythm disruption. Some crewmembers may have higher exposure to circadian disruption than most of their coworkers and thus may be at greater risk for possible health effects.

A study we completed found that travel across time zones and work during a flight attendant’s normal sleep hours were both linked to chronic circadian disruption in a group of flight attendants. The same group of flight attendants slept longer than a comparison group of teachers, but their sleep was much more disturbed.

  • Working during normal sleep hours 15 hours or more during the first trimester of pregnancy was linked to increased risk of miscarriage in a NIOSH study of flight attendants.
  • Disrupting your biological clock and sleep cycle can cause much more than problems with sleeping. It can also change normal conditions and processes in the body, including hormone levels.
  • The World Health Organization says that shift work (including the kind of circadian disruption that aircrew encounter) probably causes cancer.

What is not known

  • We don’t know what causes most health problems that may be linked to circadian disruption, including some types of cancer as well as reproductive health issues like miscarriage and birth defects. If you experience circadian disruption and have these health problems, we can’t tell if the problem was caused by your work conditions or if it was caused by something else.
  • We don’t know how much circadian disruption is safe for every person.

What can be done to reduce or eliminate exposure?

Bidding for a flight schedule to reduce circadian disruption exposures is complicated, because reducing one exposure may increase another. Seniority, lifestyle, and personal issues also affect the ability to make these choices. Here are some actions you can consider:

  • If possible, try to reduce your time working on very long flights, flights that cross many time zones, or flights scheduled for when you are normally asleep at home. These are flight conditions that tend to increase the amount of circadian disruption the aircrew is exposed to.
  • If you are pregnant or planning a pregnancy, it is important to consider your work exposures, including circadian disruption. Learn more about how your job could impact your reproductive health.
  • Adopt good sleep habits. The National Institutes of Health (NIH) and The National Sleep Foundation suggest ways to reduce the effects of circadian disruption, including:
    • As your work schedule permits, keep the same times for going to sleep and waking up that you use in your home time zone. It is best not to change your sleep schedule on days off; try to get up at about the same time. If you need to catch up on sleep, go to bed earlier.
    • Use ear plugs and eye masks to reduce noise and light when you sleep.
    • Sleep in a cool room with comfortable mattress and pillows.
      • If you are sleeping away from home, set up a quiet, very dark, comfortable, and cool hotel bedroom. Block any light coming into the bedroom under the doorways or through the windows. Cover lighted clock dials. Remember to pack an eye mask, ear plugs and clothes pins (to pin the drapes together).
    • Avoid alcohol 2-3 hours before bedtime; it will disturb sleep if taken at this time.
    • Caffeine can affect your body for five hours or more. Limiting your caffeine intake may help improve sleep.
    • Avoid heavy or spicy meals 2–3 hours before bed.
    • About 1.5 hours before bedtime, avoid using backlit electronic screens of computers, tablets, cell phones, and televisions.

Learn more about how you can help protect against the effects of many kinds of shift work, including circadian disruption, at the National Sleep Foundation Shift Work Disorder website.

If you frequently have trouble with sleep and jet lag symptoms, you can see a sleep disorders specialist for an assessment and advice. The following links can identify sleep disorders specialists and Accredited Sleep Disorders Centers near you.

For more information