Daylight-Saving Time: Time to Fall Back ... Into Bed?

From the WebMD Archives

Oct. 29, 2001 -- Sigh. The long, sunny days of daylight-saving time are over, and we humans are left to make the best of it -- more darkness, less light, for the next several months. Why is it we just want to sleep on those cold, dark winter mornings?

Turns out, that craving for sleep is part of our very human seasonal clock.

"Our bodies need more sleep during the winter months and would get more sleep if we didn't have fire and electricity" says Brian Prendergast, PhD, a postdoctoral fellow in psychology at Ohio State University in Columbus.

"One of the biggest human health issues is the invention of the light bulb," he tells WebMD. "Light is a very potent drug, not regulated by the FDA. We're already operating on a sleep debt, and when we switch on the light at night to stay up later, we're refinancing that sleep debt. I advise people to sleep more during winter. Our bodies want it."

For years, Prendergast has been studying the effects of seasonal changes on mice and men -- on the health and sexuality of both species.

His newest study looks at deer mice, shedding light on the effects of shortened days and the animal's immunity. The hormone melatonin -- only released during darkness -- seems to be at the heart of it all.

The study has implications for humans, especially those taking melatonin supplements as a sleep aid, says Prendergast. "Taking melatonin seems to have a limited effect in humans," he tells WebMD.

His study appears in the current issue of the journal Proceedings of the Royal Society of London: Biological Sciences.

For mice and other outdoor animals, environmental cues like shortened daylight hours indicate that winter's coming -- time to "thicken your fur, put on fat, hide food in the burrow," he tells WebMD.

It's all about sex and survival, he says.

"An animal can very accurately discriminate between a 12-hour and 14-hour day," he says. "Length of daylight is an animal's principal cue to increase or decrease the melatonin they secrete. Melatonin secretion becomes their internal calendar, the trigger to make adjustments for the next season."