It’s an annual ritual as familiar as the St. Patrick’s Day Parade: Spring brings sun-starved Seattleites out of hibernation, blinking in the daylight. As Seattle’s short winter days—with a mere eight hours of daily sunlight in December—give way to 16 hours of daylight by June, we often shift our own schedules in response, bedding down later and rising earlier to take advantage of the extra rays. “It’s normal for people in Seattle to sleep less in the spring and summer,” says Michael V. Vitiello, Ph.D., codirector of the Center for Research on Management of Sleep Disturbance (CRMSD) at the University of Washington.
But shifting your sleep schedule just an hour or two in response to the seasons can throw off the body’s internal clock. And, new research shows, that could put your mental health at risk. The biology behind a seasonal sleep shift is fairly straightforward: Darkness cues the brain’s pineal gland to secrete the sleepy-time hormone melatonin, resulting in the urge to sleep. Seattle’s 10 p.m. summer sunsets delay melatonin production, so we feel sleepy later. (Our kids experience this seasonal swing, too—just try putting little ones to bed while the summer sun streams into their bedrooms at 9 p.m.)
This relationship between hours of darkness and our urge to sleep is fairly simple. More complex are the mechanisms behind the body’s 24-hour clock, known as the circadian rhythm. A number of studies show that the body’s 24-hour clock actually breaks down into a series of shorter cycles called ultradian rhythms, says Vitiello.
Mess with these biorhythms at your peril: A 2015 study in the journal eLife shows that when our body’s four-hour ultradian rhythms are thrown off-kilter, mental health suffers. The study found that the four-hour ultradian rhythms are regulated by dopamine, and that disruption in these four-hour cycles may be a precursor to mental illnesses such as schizophrenia and bipolar disorder. In patients with those conditions, the four-hour ultradian rhythms can stretch to 48 hours. These findings suggest that maintaining a rock-solid sleep schedule could help prevent the onset of mental illness, say the study’s authors. Mental illness aside, people with irregular sleep patterns see a dip in their creativity, productivity and mood, says David C. Chang, M.D., head of sleep medicine at The Polyclinic. “Poor sleep quality affects the mood, the ability to be creative and how quickly we can get things done at work.”
Bright morning light sets the body’s clock, boosting daytime alertness and encouraging nighttime sleepiness
Shifting sleep patterns hurt our health because our body clocks don’t like disruption, says Chang. “The medical literature shows that it’s ideal to stick to the same sleep schedule year-round, regardless of the season.”
So what does this mean in Seattle, where 4:30 p.m. December sunsets and 4:30 a.m. June sunrises conspire to keep us off-kilter?
The keys to keeping the body clock on an even keel from season to season are a highly consistent daily sleep schedule and the right daily balance of light exposure and darkness, says Chang. Start by sticking to your sleep routine; Chang recommends flexing your bedtime and waking time by no more than an hour—even on weekends.
A well-timed blast of light can make it easier to stick to that strict sleep schedule, because bright morning light sets the body’s clock, both boosting daytime alertness and encouraging nighttime sleepiness. For the most benefit, Change recommends that his patients get two hours of bright light in the morning.
Light therapy lamps (available at health retailers and many big-box stores) drench you in simulated sunlight to help regulate sleep patterns. Chang steers his patients toward full-spectrum light bulbs, like the Reveal line by GE. “They can give a similar effect as more expensive lamps and cost less.”
Equally important is turning off electronics two hours before you’d like to be asleep. Light produced by screens can stall sleep for hours, because nighttime light exposure impacts melatonin production.
“The brain doesn’t know that the light is coming from a screen and not the sky,” Chang says. By encouraging the body’s natural response to darkness—melatonin production, followed by sleepiness—this electronic pause before bed helps prevent seasonally induced sleep shifts, insomnia and disrupted sleep patterns.
“You can imagine the pushback I get from my patients who work in tech at Amazon and Google when I give the two-hours-before-bed advice,” says Chang. But the tradeoff is worth it: A steady year-round sleep rhythm helps boost productivity, creativity and mood, and may protect mental health, to boot. Nighty night.