Artificial light interrupts circadian cycle

Dear Doctors: We live in Northern California, and every time we have high winds, the electric company shuts off power because of the fire danger. We use candles and lanterns to light the house, and my husband thinks that he sleeps better on those nights. Do you think there’s a connection?

Dear Reader: We humans, like most creatures on this planet, are keyed to the daily cycle of light and dark. It’s reflected not only in our habits and behaviors, but research shows that it plays out at the cellular -- and even the molecular -- level, as well. Known as the circadian cycle, and often referred to as the body clock, it guides metabolic and biological processes throughout our bodies. A number of these, including the regulation of body temperature, hormone secretion and alertness, play key roles in preparing the body to switch from wakefulness to sleep.

Studies have shown that exposure to even small amounts of artificial light can delay the body’s important sleep prep. It means that with the very first campfire humans lit to push back the night, they disrupted the sensitive mechanisms of the circadian cycle. As firelight gave way to candlelight, then to gas light and now to electric light, that disturbance grew progressively more pronounced. That’s because, as we now know, spending time in bright light slows production of melatonin, which is the hormone whose nighttime spike helps make us sleepy. The advent of blue light in all of the screens we use has also been shown to wreak havoc on sleep quantity and sleep quality.

In a small study conducted by researchers at the University of Colorado at Boulder, eight participants camped in a wilderness area so remote, it was free of any artificial light. The campers left all portable light sources behind and lived solely by natural daylight. Lab tests showed that after only a week, their daily melatonin rhythms, as well as their individual sleep schedules, were syncing to the daily ebb and flow of light. The takeaway was that, due to reduced exposure to sunlight in our largely indoor lives, and the near-constant presence of electric lights, human circadian physiology has been altered.

Elizabeth Ko, MD and Eve Glazier, MD

Interestingly, another study found a wide range in tolerance to artificial light. For some participants, the dim glow of just a few candles caused the same drop and delay in melatonin production that others in the study experienced only in the presence of sustained bright light. All of which adds up to the fact that yes, it’s entirely possible your husband’s sleep improves when his days and evenings are free from screens and electric lights. This is important because insufficient sleep and low-quality sleep are linked to a number of serious health conditions. These include high blood pressure, depression, obesity and coronary heart disease. The sleep deficit in the United States is so severe, the Centers for Disease Control and Prevention has flagged it as a public health problem.

You don’t need to go cold turkey on electrical light. But the research is clear: Spending more time in daylight and dimming the lights -- and screens -- after dark can add up to better sleep.

The UCLA Sleep Disorders Center faculty is a multidisciplinary group actively involved in basic and clinical research aimed at determining the conditions that result in sleep disturbances and identifying successful treatments to overcome and prevent sleep disturbances in children and adults. Learn more and schedule an appointment.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)


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