If you are sleeping at the same time everyday, your sleep is anchored. The time here is a special time. It is biological time. This means that, according to your biological clock, your sleep happens everyday at the same time. If your duty times are constantly changing like a lot of my railway friends out there, or you are constantly crossing time zones like a lot of my aviation friends out there, there is a good chance that you are not getting your eight hours of sleep at the same biological time each day. But that’s OK, you don’t actually need a full eight hours of shut-eye at the same time.
In the research I have looked at, four hours of anchor sleep was obtained at the same biological time. But my hunch is that you might only need two to four hours of anchor sleep. “Why would you need it?” you may ask. Anchor sleep keeps your circadian rhythms stable and synchronized to each other and to wall clock time. Again you may ask “Why do my circadian rhythms need to be stable and synchronized?”
I am glad you asked. Stable and synchronized circadian rhythms will keep you healthier. If your shifts are all over the place or you are constantly bouncing from one time zone to another, chances are that your sleep periods are irregular. By sleeping at all sorts of times, your biology will be constantly stressed by trying to catch up and adjust to the new sleep times. At some point, it will just give up and your circadian rhythms will become desynchronized to each other and to wall clock time. In other words, your body will no longer know what time it is; you will have lost your biological time. This can make you feel pretty awful, and if you are not fatigued all the time, your fatigue will hit unpredictably. If your biology gets desynchronized frequently for many years, you can get really sick, like cancer sick.
Anchor sleep can help keep you healthier in the short term and reduce your risk of developing a serious illness in the long term. It can also help with fatigue. Your overall energy should improve and instead of being fatigued all the time, your fatigue levels will become predictable. If they are predictable, you can manage them better by taking action before you expect to be fatigued.
Here are some simple steps to use anchor sleep to keep your circadian rhythms stable and synchronized, improve your energy and manage fatigue:
- Choose a home base time zone to which you will synchronize your biological clock.
- Choose a home base night sleep period of eight hours that works for you. Think about how you sleep on your holidays to figure out what works for you. If you are a night owl, don’t feel you have to be in bed at 22:00; choose a later sleep period. If you are a morning lark, choose an earlier period.
- Check your schedule to see when you will have no choice but to be awake.
- Now compare your mandatory awake periods to your eight hour sleep period. Find a block of between two to four hours in your eight hour sleep period when you can sleep everyday.
- Get your anchor sleep in the four hour block of home base time as often as possible, every day if you can.
- Be very protective of this sleep time, don’t let anything take it away. This means that if your home base time is in the Eastern time zone and your anchor sleep is between 20:00 and 24:00, nothing disturbs you during this period no matter where you are. NOTHING! Not kids, spouses, pets, phone calls, or Twitter! NOTHING! If you travelled from Toronto to Vancouver, this block of protected anchor sleep time would be from 17:00 to 21:00 local time.
- Next, be very conscious of your fatigue risk periods. There are two for everyone. The first, and worst, occurs at night during the circadian trough of about six hours between 24:00 and 06:00. With the highest fatigue levels (and accident rates) occurring between 01:00 and 05:00. The second fatigue risk period occurs during the post-lunch dip of about two hours between 14:00 and 16:00. These fatigue risk periods are not precise. Pay attention to your alertness and fatigue levels close to these periods to figure out your exact risk periods.
- Take action before your fatigue risk periods by squeezing in a nap, consuming caffeine or turning up the lights really bright (see my article on what colour of light to avoid).
 See for examples:
(A) Mills, J. N., Minors, D. S., & Waterhouse, J. M. (1978). Exogenous and endogenous influences on rhythms after sudden time shifts. Ergonomics, 21, 755-761.
(B) Minors, D., & Waterhouse, J. (1981). Anchor sleep as a synchronizer of rhythms on abnormal routines. International Journal of Chronobiology, 7(3), 165-188.
(C) Minors, D., & Waterhouse, J. (1983). Does ‘anchor sleep’ entrain circadian rhythms? Evidence from constant routine studies. Journal of Physiology, 345, 451-467.
 See for examples:
(A) Kecklund, G. & Åkerstedt, T. (1995). Time of day and Swedish road accidents. Shiftwork International Newsletter, 12(1), 31.
(B) Mitler, M., Carskadon, M., Czeiler, C., Dement, W., Dinges, D., & Graeber, R. (1989). Catastrophes, sleep, and public policy: Consensus report. Sleep, 11(1), 100-109.