“I recommend that you take care of the minutes; for the hours will take care of themselves.” Lord Chesterfield 1694-1773
There’s an absolute rhythm to our bodies. Not just humans, but many animals (certainly all mammals) demonstrate behavioral and physiologic evidence of an innate 24 hour cycle. For sure, some of our daily rhythms represent reactions to cycling changes in light, temperature, and other environmental stimuli. But, research shows that when we are placed in an environment devoid of external cues (e.g. a room without windows that is dark all the time or brightly lit all the time), our biologic clocks continue to cycle in a relatively constant sleep-wake cycle; and apparently, these set cycles can continue indefinitely in such environments. What is also interesting, is that our internal clock runs on a 25 hour cycle rather than 24 hours. Though puzzling initially, this innate 25 hour day explains why it is easier to stay up later during holidays but hard to get back on a schedule of earlier rising. Additionally, it explains why traveling from east to west is easier than the reverse. . .because we adapt better to staying up later and “sleeping in” than the opposite schedule. This biologic clock is scientifically termed our circadian rhythm— a phrase which is derived from the Latin, circa, meaning “about” anddia meaning “day” or 24 hours. There are some interesting, and predictable health consequences to disruption of circadian rhythm; and I want to share them with you this week.
In general, circadian rhythm supports our sleep through most of the hours of darkness and our “awake time” through daylight hours. Biologic rhythms generate a definite increase in both pulse and blood pressure on awakening. Our body temperatures are programmed to increase during the day and decrease at night. Also, many of our naturally-produced hormones rise and fall in response to circadian rhythm.
When we intentionally or unintentionally disrupt our normal circadian rhythms, we feel the consequences. Jet lag and shift work both represent such consequences. It may take days or even weeks for all the body’s circadian rhythms to reset after an ‘across-the world’ flight. Symptoms include: upsets in the sleep/wake cycle, headaches, irritability, and a general sense of malaise. Significantly, as we are now in prime football season, team game performance can suffer dramatically by cross-country flights. Shift workers can experience all of the above symptoms on a repetitive basis. Even staying up two to three hours after our normal bedtimes can cause us to be more irritable and have a dull headache the next day. Additionally, some illnesses manifest in very definite circadian rhythm. Most asthma attacks occur between two and six o’clock in the morning. Heart attacks are much more common in the morning than any other time of day. With such knowledge, we can prescribe and take medications at the time of day they are likely to do the most good. There’s even a study of Icelandic pilots who fly international routes that shows them to have 25 times the likelihood of developing skin cancer than average people. Though increased radiation exposure probably plays a role, the explanation is felt to be at least partially due to disturbed circadian rhythm which alters melatonin levels generated in the brain; these levels ultimately affect skin pigmentation. Additionally, since melatonin seems to be an important hormone in our sleep/wake cycle generally, its natural decrease in production as we age might help to explain why the elderly have more insomnia and daytime drowsiness.
Let’s get back to rotating shifts for a minute. Peptic ulcer disease in shift workers is eight times that of the normal population. Chronic fatigue, sleep problems, cardiovascular mortality, divorce rate, substance abuse, and depression are all increased in shift workers. Research is active in several countries as various laboratories are studying the effects of light and non-photic stimuli on circadian rhythm. Hopefully, this information will help to control such phenomena as jet lag, shift-rotation syndrome, and seasonal affective disorder (‘Winter Blahs’ where people experience depression and disturbed sleep patterns in the months when days are shorter and hours of sunlight are reduced). Additionally, circadian factors are also being studied in the areas of cardiovascular disease, obesity, and optimal timing of cancer chemotherapy.
On a practical note, one can benefit from regular exercise, regular bedtime, and limited use of caffeine and/or sleeping pills. Also, regular exposure to light. . . especially natural sunlight can be very helpful in maintaining and resetting circadian rhythms. Melatonin supplementation can be helpful, but its routine use is still controversial. And, on a philosophic note, I must conclude with a few words on our conscious use of time each day. We have opportunities to achieve, and mature, and influence other people positively each day of our lives. Though our circadian rhythms are set, we can strive to use our waking hours productively and wisely.
“We all run on two clocks. One is the outside clock, which ticks away our decades and brings us ceaselessly to the dry season. The other is the inside clock, where you are your own timekeeper and determine your own chronology, your own internal weather and your own rate of living. Sometimes the inner clock runs out long before the outer one, and you see a dead man going through the motions of living.” Max Lerner 1952
Stephen L. Hines, M.D.
September 2000
