Birds have them. Bees have them. Humans have them too. They’re internal clocks that regulate when we get up, when we go to bed, and a whole lot of activities in between.
Internal clocks and circadian rhythms
We all have a number of internal clocks every bit as synchronized as the finest Swiss watch. These clocks are clusters of cells in areas such as the heart, lungs, and the liver. The master body clock called the suprachiasmatic nucleus (SNC) is located in the hypothalamus, an area of the brain that controls the release of a whole host of hormones, including melatonin.
It’s melatonin that influences when we sleep and when we wake, and it’s closely tied to the 24-hour cycle of daylight. As light fades, the SNC triggers the release of melatonin, which makes us sleepy. As the sun starts to rise and we are exposed to increasing light, the body inhibits melatonin release. Genes have also been found to influence our daily sleep-wake cycle, called the circadian rhythm.
Thanks to electric lighting, we are able to prolong our day. That puts us at odds with our circadian rhythms, which would naturally have us sleep for longer periods during winter darkness. The possible result is a disturbance in our normal sleep-wake cycle, leaving us feeling sluggish, unproductive, and maybe even a little low. Some may experience winter depression, often called seasonal affective disorder.
When the clock goes awry
Since circadian rhythms influence so many of the body’s functions, it’s no surprise that health can suffer when there’s an upset in the body’s normal cycle.
Researchers at Columbia University who looked at population studies found that reduced hours of sleep and metabolic problems, such as diabetes, often occurred together. They concluded that disrupted sleep patterns can lead to the release of stress hormones that, in turn, lead to hypertension and insulin resistance.
Yale School of Medicine studies looking into the genetic control of circadian rhythms found that we have lowered resistance to infection at certain times of the day. Researchers have also found a link between gene mutations that govern circadian rhythms and cancers of the breast, ovaries, and colon.
Sleep-wake cycles not only have an impact on physical health, but also play a part in mental health. The existence of seasonal affective disorder has become well known. What’s less well known is that other mental illnesses are also linked to the body’s sleep-wake cycles. Those with depression, bipolar disorder, and schizophrenia often experience severe circadian rhythm disruptions, a symptom thought to be linked to genetic control of the body’s internal clock.
Beating the clock
Penny Johnson has been coping with winters in Canada’s extreme north since 1981 when she and her husband moved to Inuvik, Northwest Territories. Known as the “land of the midnight sun,” it’s also known for its prolonged winter nights. During the longest periods of darkness, says Johnson, light would appear as only a short period of dusk.
“I think it’s important to get out of the house and add some type of activity to keep you active, to provide you with a different option than going home and hunkering down in front of the television,” says Johnson.
She and her husband arranged their work schedules so they could get out for a ski in that dusk period. In addition to staying active, the couple planned regular get-togethers with friends to avoid spending hours cooped up in their house.
Now living farther south in Yellowknife, Johnson says there are more leisure opportunities in winter, including a large well-lit recreation center where she can go for an indoor jog in shorts and a T-shirt. She and her husband have embraced the outdoors, enjoying cross-country skiing and skidooing.
Johnson admits, however, that the darkness can become oppressive. She ensures her family eats a balanced diet and takes vitamin D supplements. She also recommends, for those who can, taking a mid-winter holiday to a warm location.
Sometimes our schedules just can’t follow our body’s natural clock, whether we’re working the night shift, caring for a newborn, or traveling across time zones. Scheduling daily activities so they’re in sync with our circadian rhythms, whenever possible, can help us feel healthy and get the most out of our days.
Morning light cues the body to slow melatonin production. As we wake up, our body temperature starts to rise and our digestive system becomes more active. Mornings are generally a time when concentration, alertness, and memory are at their height, so it’s a good time to do your most challenging work and save easier tasks for later in the day.
In the afternoon, coordination, reaction time, muscle strength, and circulation are at their peak, making it a good time to book a squash game, take a fitness class, or go for a walk. In mice, exercise has been found helpful for keeping circadian rhythms on track, especially in advanced age. For some people, however, physical activity too close to bedtime may actually make falling asleep more difficult.
As daylight fades, melatonin is released and we start to feel sleepy. We can make the most of that effect by creating a bedtime ritual—a quiet time with a book, herbal tea, some calming music. A light evening snack, such as cheese and whole grain crackers, can help you take advantage of that melatonin mellowness, improving your chances of a restful sleep.
Our circadian rhythms perform wondrous feats every day, coordinating the daily ebb and flow of body chemistry and functions. Factors such as artificial light, travel, and even the changing seasons can affect those natural cycles. Doing what we can to support our sleep-wake cycles can be important for not only maintaining good health, but also ensuring that we’re well rested and energized so we can enjoy life.