We've all heard of natural rhythms, the daily, monthly and yearly cycles that govern our planet. And while some people try to live in harmony with such things, as a society we tend to dismiss the subject as New Age nonsense.
But we do so at our peril. Consider this: sleep-disturbing shift-work has been linked to breast cancer in nurses and to diabetes and obesity in the general population.
The frequency of strokes and seizures is correlated with certain phases of the moon. And heart failure follows both daily and annual cycles, striking more often in early morning during the winter-spring season.
Just because we've banished night with artificial light and winter with central heating doesn't mean that our bodies are no longer governed by the geophysical pulses of night and day, tides, lunar cycles and seasons.
Circadian (from the Latin circa for "around" and diem for "day") rhythms, for example, are so deeply embedded in our genes, our daily body clock still runs, even if we are shut away in the dark.
Sleep/wake cycles, blood pressure, reaction time, alertness, digestive secretions, thirst, appetite - all are governed by circadian rhythms. Shorter cycles, called ultradian rhythms, operate within the 24-hour day, such as the 90-minute REM sleep cycle, the four-hour nasal cycle and the three-hour cycle of growth hormone production.
And so it goes, cycles within cycles, right down to the beating or pulsing of individual cells.
Although these rhythms are endogenous (proceeding from within the body), they are ultimately set by external influences like changing light or temperature.
If you fly, for instance, to a time zone on the other side of the world, your body clock will gradually adjust. But fly back and forth every week or so, as airline pilots do, and the chronic disruption of your body clock can become a serious health hazard.
We are particularly sensitive to light. Both the intensity and colour of light that enters through our eyes affects the production of melatonin, a hormone that regulates a number of bodily functions.
Melatonin is strongly associated with sleep, peaking at about 9 p.m. and dropping to barely detectable amounts during the day. There is a correlation between high light levels/decreased melatonin production and an increased risk of cancer.
Although shift work is unavoidable for many people, they can still limit the disruption of their circadian rhythm by sleeping in a darkened room during the day.
And as for the rest of us, remember that cities are flooded with light at night, so pull the blinds or drapes and maximize your melatonin production.
If you are a shift worker or if you suffer from insomnia, you should get your melatonin level checked. If you are down a pint or two, a small dose of a melatonin supplement will fairly quickly restore balance.
Aside from doing a favour to several important bodily functions that are melatonin-dependent, you will probably sleep better. Be advised, however, that larger doses of the hormone (a cancer treatment) trigger unpleasant dreams, though these usually pass after a couple of weeks.
