Dr. Nada Milosavljevic
CIRCADIAN RHYTHM: THE CHALLENGE OF KEEPING TIME
Many of the cycles in nature – like bears hibernating or deciduous trees losing their leaves – are often calibrated by the light of the sun. Its daily appearance and disappearance over weeks and months is like a slow-rocking cradle for our systems, balancing between periods of activity and rest. Sleep is a crucial part of maintaining this balance for humans. The cycle of sleeping and wakefulness in humans is shaped by “circadian rhythms,” or activities that follow a daily cycle. The chemical mechanism that is central to the sleep-wake cycle for humans is melatonin, which is a hormone that induces sleep. When an individual’s optic nerves receive less light, that triggers a signal to the brain to make more melatonin.
To maintain healthy sleep patterns, one should strive for as much continuity in bedtime habits as possible on a day-to-day basis. This can be a challenge in today’s world with the constant temptation of looking at screens of one sort or another, all of which emanate a stimulating light that throws off the gradual descent into sleepiness. The importance of circadian rhythms can be seen clearly in the sleeping problems encountered by some of the “outliers” in the circadian patterns of the human population – teens and the blind.
Because circadian rhythms develop in conjunction with a person’s eyes being exposed to light, the blind often don’t have a natural circadian rhythm. Instead, they have a “free running rhythm,” which can lead to severe sleep disorders; researchers have found that the greater the degree of blindness, the more likely one will suffer from a “free running rhythm” sleep pattern. By administering melatonin in regular doses to blind people suffering from sleep disorders, doctors have often succeeded in approximating a 24-hour sleep cycle for these patients.
Although it is generally true that exposure to light is a decisive influence on the secretion of melatonin in the brain and therefore decisive in shaping the circadian rhythm, adolescent sleep patterns provide the exception that proves the rule. For some yet-to-be-determined reason, the circadian rhythms of children hitting puberty starts to shift two full hours later, both for bedtime and for waking.
Unfortunately for many teens around the world, this shift in circadian rhythms comes into direct conflict with school days that begin early in the morning. Teens pay the price by suffering from sleep deprivation. Many teens try to “make-up” for the sleep deprivation they feel during the week by sleeping for longer times during the weekend, waking up in the late morning or even early afternoon. This is not generally effective; in fact, some researchers believe that “sleeping in” gives the teens something similar to “jet lag” when they wake up for school on Monday morning.
In places like New England, the amount of time the sun stays in the sky can differ greatly between seasons: from about nine hours of sunlight in December to 15 hours of sunlight in June. While this represents a large swing in daylight hours, the process is gradual, allowing most people to slowly adjust to these significant variances.
The change in seasons, while gradual, does affect some people negatively. These people suffer from “seasonal affective disorder” (or SAD) in the winter. Some researchers have intimated that a portion of the population may secrete unusually large amounts of melatonin during the winter, which can lead to depressive symptoms. One effective treatment is using “light therapy,” in which patients can use a bright “SAD” lamp from 20 to 60 minutes every morning during the fall and winter. This can decrease the amount of melatonin that is secreted in the brain. This therapy should be maintained consistently so as to not lose ground in creating positive mood changes through phototherapy.
For those of us who grew up in New England and similar climates, a change in seasons is often welcome: it promises both variety and progression throughout the year. We’d certainly miss the beauty that these changes bring, like the dazzling fall foliage. Although these changes can provoke depression or even just the blues, there are ways to minimize the potential negative impacts in reacting to reduced light. Being conscious about keeping a regular bedtime and availing yourself to minimally invasive therapies like phototherapy can help you maintain healthy sleep habits throughout the year.