Shiftwork adaptation technique: reset your circadian rhythm by fasting

Researchers in the Division of Sleep Medicine at Harvard Medical School and Beth Israel Deaconness Medical Center in Boston published a paper in this week's journal Science in which they cite the discovery of a second circadian clock in humans which appears to be triggered by fasting. The authors note that this discover could be used to reduce the effects of jet lag and could also help shiftworkers adapt to night work.

Human's primary internal clock is triggered by light. This is the clock we hear about most often -- getting exposure to bright light to increase alertness and avoiding light when trying to sleep. This second clock is triggered by food. The evolutionary underpinnings of the clock seem to be that for early humans not to have food available was a life-threatening situation. If they could not obtain food, their bodies kicked into an extra level of alertness to enable them to continue to search out food. Dr. Clifford Saper, one of the authors of the paper, noted it takes about 16 hours of fasting for this second clock to kick in and override the light-based clock.

This will be particularly important for shiftworkers on a rotating schedule as they prepare for the night shift, or a fixed schedule night shift worker returning to work after days off. A shiftworker might be able to reset his or her circadian rhythms faster by avoiding eating anything during the day prior to the night shift. This would raise alertness levels and the shiftworker would be able to then eat during the overnight shift. The same could also be used by air travelers to avoid jet lag. If the air traveler avoid eating ANYTHING on the flight on a flight from New York to Australia, he or she would better adapt upon arrival.

This will undoubtedly be studied further, so it's subject to modification, but the researchers are credible, and the work being published in the journal Science lends even more credibility. I think there's enough at this point that you might consider using this technique if you're having trouble adapting to night shifts.

Reference:
"Differential Rescue of Light- and Food-Entrainable Circadian Rhythms."
Patrick M. Fuller, Jun Lu, and Clifford B. Saper.
Science Vol. 320. no. 5879, pp. 1074 - 1077.
Published online on 23 May 2008.

The study of circadian rhythms

The roots of the study of biological rhythms reach back to the 1700s and the work of the French scientist de Mairan, who published a monograph describing the daily leaf movements of a plant. De Mairan observed that the daily raising and lowering of the leaves continued even when the plant was placed in an interior room and thus was not exposed to sunlight. This finding suggested that the movements represented something more than a simple response to the sun and were controlled by an internal clock.

De Mairan’s apt observations illustrate one critical feature of circadian rhythms- their self-sustained nature. Thus, almost all diurnal rhythms that occur under natural conditions continue to cycle under laboratory conditions devoid of any external time-giving cues from the physical environment (e.g., under constant light or constant darkness). Circadian rhythms that are expressed in the absence of any 24-hour signals from the external environment are called free running.

The persistence of rhythms in the absence of a dark-light cycle or other exogenous time signal (i.e., a Zeitgeber) seems to indicate the existence of some kind of internal timekeeping mechanism, or biological clock. However, some investigators have pointed out that the persistence of rhythmicity does not necessarily exclude the possibility that other, uncontrolled cycles generated by the Earth’s revolution on its axis might be driving the rhythm (see Aschoff 1960).

The hypothesis that such uncontrolled geomagnetic cues might play a role in the persistence of rhythmicity can be refuted by a second characteristic feature of circadian rhythms: These cycles persist with a period of close to, but not exactly, 24 hours. If the rhythms were exogenously driven, they should persist with a period of exactly 24 hours. The seeming imprecision is an important feature of rhythmicity, however.

As Pittendrigh (1960) demonstrated, the deviation from a 24-hour cycle actually provides a means for the internal time-keeping system to be continuously aligned by and aligned to the light-dark environment. This continuous adjustment results in greater precision in controlling the timing, or phase, of the expressed rhythms, because little drift is allowed to occur before the rhythm is “reset” to the correct phase.

A third characteristic property of circadian rhythms is their ability to be synchronized, or entrained, by external time cues, such as the light-dark cycle. Thus, although circadian rhythms can persist in the absence of external time cues (meaning that they are not driven by the environment), normally such cues are present and the rhythms are aligned to them. Accordingly, if a shift in external cues occurs (e.g., following travel across time zones), the rhythms will be aligned to the new cues. This alignment is called entrainment.
Initially, it was unclear whether entrainment was achieved by modulating the rate of cycling (i.e., whether the cycle was shortened or lengthened until it was aligned to the new cues and then reverted to its original length) or whether entrainment was achieved by discrete “resetting” events.

Experiments resulting from this debate led to fundamental discoveries. For example, researchers discovered that the organism’s response to light (i.e., whether a cycle advances, is delayed, or remains unchanged) differs depending on the phase in the cycle at which it is presented (Pittendrigh 1960). Thus, exposure to light during the early part of the individual’s “normal” dark period generally results in a phase delay, whereas exposure to light during the late part of the individual’s normal dark period generally results in a phase advance.

In addition to the timing of the light exposure, the light intensity can modulate cycling periods when organisms are left in constant light. Thus, exposure to brighter light intensities can lengthen the period in some species and shorten it in other species. This phenomenon has been dubbed “Aschoff’s rule”(Aschoff 1960). Ultimately, both mechanisms of entrainment appear to be aspects of the same thing, because the consequences of Aschoff’s rule can be predicted or explained by the phase-response curves to light.

Although the light-dark cycle clearly is the major Zeitgeber for all organisms, other factors-such as social interactions, activity or exercise, and even temperature-also can modulate a cycle’s phase. The influence of temperature on circadian rhythms is particularly interesting in that a change in temperature can affect the phase of a cycle without substantially altering the rate of cycling.
This means that the cycle may start at an earlier or later-than-normal time but still have the same length. On the one hand, this ability of the internal clock’s pacemaker to compensate for changes in temperature is critical to its ability to predict and adapt to environmental changes, because a clock that speeds up and slows down as the temperature changes would not be useful.
On the other hand, temperature compensation also is rather puzzling, because most kinds of biological processes (e.g., biochemical reactions in the body) are accelerated or slowed by temperature changes.

Ultimately, this riddle has provided a clue to the nature of the internal clock- that is, the fact that circadian rhythms have a genetic basis. Such a program of gene expression would be more resistant to temperature alteration than, for example, a simple biochemical reaction. Two final properties of circadian rhythms also provide important hints of the rhythms’ makeup. One of these properties is the rhythms’ ubiquity in nature: Circadian rhythms exist in a broad array of biological processes and organisms, with similar properties and even similar phase-response curves to light.

The other property is that circadian rhythms appear to be generated at the cellular level, because the rhythms of unicellular organisms (e.g., algae or the dinoflagellate Gonyaulax) are much the same as rhythms of highly complex mammals. Both of these observations suggest that a cycle in the activation (i.e., expression) of certain genes might underlie the timekeeping mechanism.

By Martha Hotz Vitaterna, Ph.D., Joseph S. Takahashi, Ph.D., and Fred W. Turek, Ph.D.
MARTHA HOTZ VITATERNA, PH.D., is a senior research associate in the Center for Functional Genomics, Northwestern University, Evanston, Illinois. JOSEPH S. TAKAHASHI, PH.D., is the director of the Center for Functional Genomics, the Walter and Mary E. Glass Professor in the Department of Neurobiology and Physiology, and an investigator at the Howard Hughes Medical Institute, Northwestern University, Evanston, Illinois. FRED W. TUREK, PH.D., is the director of the Center for Sleep and Circadian Biology and is the Charles T. and Emma H. Morrison Professor in the Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois.

Source: http://www.niaaa.nih.gov/publications/arh25-2/85-93.htm

Related posts:
* Overview of circadian rhythms
* Glossary of shiftwork terms: shiftwork, sleep, circadian rhythms, and more
* The drivers of human alertness and sleep

The drivers of human alertness and sleep

Your alertness is the result of nine elements, what Dr. Martin Moore-Ede in his book The Twenty-Four-Hour Society termed the nine switches of alertness. Knowing these elements can help you better manage your environemtn and behavior to improve your alertness or help you sleep. The nine elements are:

1. Interest, opportunity, or sense of danger -- when you are mentally engaged or threatened in some way, your body rises to the challenge by increasing alertness.
2. Physical activity -- when you are physically active, you increase your alertness. This effect can last for a while, making sleep difficult after intense exercise.
3. Time of day on your circadian clock -- if your body is telling you it's night time, your alertness will drop. You can reset your circadian clock (as evidenced when you travel across time zones) but it takes time and careful attention if you're a shiftworker.
4. Your sleep "bank balance" -- if you have gotten inadequate sleep over the past few days, your alertness will suffer.
5. Ingested nutrients and chemicals -- caffeine and other substances have a stimulating effect while tryptophan and sleeping pills will encourage sleep.
6. Environmental light -- bright lighting wakes you up and dim lighting tends to make you sleepy.
7. Temperature -- warm and stuffy rooms make you sleepy while cold, bracing increases alertness.
8. Sound -- loud, erratic noises increase alertness while soft sounds and white noise reduce it.
9. Aroma -- This last one, aroma, has somewhat less research to support it, but there is at least some evidence that certain aromas have a stimulating effect while others have just the opposite. Scents like lemon and peppermint have been found to increase alertness.

Keep these factors in mind and use them to your advantage.

Adapting to night shifts -- helping shiftworkers adapt and avoid shiftworker maladaptation

Adapting to nighttime or daytime work requires synchronization of your biological clock (which controls your circadian rhythms) to the work schedule. Maladaptation results if your biological clock is not adjusted to the work schedule. To adapt the biological clock, shiftworkers must be exposed to daylight (or bright artificial light of 1,000 lux or more) both upon awakening and
throughout their active periods (for example, during work hours).

Also, shiftworkers must avoid bright light from approximately three hours prior to the end of their long sleep period.

The only way to fully adapt to nightshift schedules is to reset the biological clock so that energy peaks during nighttime. Work must take place under artificial light (of at least 1000 lux) that mimics daylight. Although this is a far lower level than actual daylight, it will seem far brighter than normal indoor lighting which is typically in the 300-400 lux range. Sleep must take place in a dark and noise-free environment for approximately seven to eight hours. Failure to control daylight and/or light exposure is a significant contributor to fatigue and shiftwork maladaptation.

Maladaptation to shiftwork schedules and lack of energy-restoration sleep can result in persistent sleepiness, low energy, lack of motivation, and depression; in performance degradation during duty hours; and in increased safety risk.

Other health effects such as increased incidence of cardiovascular disease, gastrointestinal disorders, and sleep disorders have been historically documented in populations subjected to shiftwork maladaptation. The combined effects of disrupted sleep and biological clock disorganization can lead to endurance degradation, jet-lag-like symptoms, irritability, depression, and, in extreme cases, psychosis.

Optimizing Adaptation to Shiftwork
Optimizing shiftworker rest, while preventing shift lag (inadequate adjustment to shiftwork schedules), can contribute significantly to shiftworker adaptation to work and life aboard a maritime vessel.

Listed below are some recommendations that can prevent shift schedules from inducing short and disrupted sleep periods and shift lag.

Avoid allowing staff to work more than 12 hours in a 24-hour period. Count
these 24 hours from the time shiftworkers wake up from their longest daily sleep
period (not naps).

Total Adaptation to Night Work

• Provide bright-light exposure (e.g., fluorescent bulbs of at least 1000 lux) during the work period. Note: This artificial-light exposure can only be implemented in environments where night vision is not required for performing normal duties (so, for instance, ambulance drivers who will need to be able to drive in the dark at night should not be exposed to bright artificial lighting between calls).
• Provide nightshift staff with small-size meals that promote energy and alertness (high protein, low fat, low sugar, low starch, no dairy products or turkey).
• Adjust meal times so nightshift personnel can eat a brunch on waking (at approximately 1:00 pm), including brewed coffee and breakfast foods, if desired.
• Adapt the cafeteria services to accommodate crewmember needs. This accommodation supports both safety and crew morale.

Partial Adaptation to Night Watch or Work Schedules
When bright lights cannot be used in the work environment, stick to the following recommendations:

• Reduce the duration of the shift in order to minimize the impact of endurance degradation on safety. Promote exercise in the evening hours.
• Allow shiftworkers from any shift ending in the morning hours to retire prior to sunrise, and to sleep at least seven to eight hours free of noise and with absolutely no interruptions.
• Overtime should be scheduled to occur after wake-up time (e.g., from 2:00 pm to 6:00 pm), whereas leisure activities should be scheduled for the evening hours.

Source: http://www.uscg.mil/hq/g-m/cems/PDF/light_management.pdf.

Suggested reading on circadian rhythms and light exposure

A couple of articles I've been reading that I wanted to let you know about.

An article on SeparationsNow.com called "Clocking On" discusses circadian rhythms and how they work.

Seasonal affective disorder (or SAD) is a mental health issue that has some similarities with shiftwork since light exposure is a critical element to good health and mood. An article in today's issue of The Gazette (Colorado Springs, Colorado, USA) Wintertime depression: a sad state provides a nice overview.

Ed