Why Are You So Tired After Sleeping In?

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Raise your hand if you can’t believe it isn’t Friday yet. Are you counting the hours until you're "allowed" to sleep in past noon and crawl to your local brunch spot, just in time to devour some eggs Benedict before the kitchen closes at 4 p.m.? Tempting as it is to hit the snooze button and live out that dream, consider this: According to a new report by the Harvard-based Nurses’ Health Study, spending more than eight hours per night in the land of Nod may be doing you more harm than good.

In this recent study, researchers monitored a group of middle-aged female nurses over a span of several years. In 1986 and 2000, the participants answered questions about their sleep habits. As a follow-up, the researchers tested the women’s memories and cognitive skills biannually from 1995 to 2001 (by this time, the participants were in their 70s, but free of stroke or mental illness). Subjects who reported sleeping five hours or fewer per night and those who slept nine hours or more demonstrated weaker memories and cognitive function than those who slept seven to eight hours nightly. The scientists estimated that, on average, the women who over- and under-slept were mentally two years "older" than those who got the optimal seven to eight hours of beauty rest.

According to Elizabeth Devore, an instructor in medicine at Brigham and Women’s Hospital in Boston and head of the study, “[These] findings suggest that getting an ‘average’ amount of sleep, seven hours per day, may help maintain memory in later life, and that clinical interventions based on sleep therapy should be examined for the prevention of [mental] impairment.” It’s interesting that Devore specified seven hours and not the widely acclaimed magic sleep-number of eight — especially since the study showed seven to eight hours as the optimal range. One more hour to carpe diem, perhaps?

While a few lazy days here and there won’t hurt you, there’s a reason why sleeping in feels so good at the time and so bad afterwards. Your body’s circadian pacemaker (a cluster of cells in the hypothalamus) causes that feeling of drunkenness that you get when you overindulge in ZZZ’s. This pacemaker controls hunger, thirst, and sweat — all those essential internal rhythms. When dawn breaks and light hits your eyelids, these cells register the time and send out chemical signals to the rest of their brethren, ensuring all the cells in your body are on the same clock, ready to start the energy-consuming day. Remaining in bed after the cellular wake-up alarm has already sounded disrupts this regulatory process. Your cells begin their energy cycle ahead of the game, causing you to feel fatigued and discombobulated when you do choose to rise.

Granted, some people feel sluggish on any more than five hours, and others are total garbage without their mandatory nine (followed by a Trenta Red-Eye). Ultimately, it’s all about giving your body what it needs. If you're having trouble dragging yourself out of bed or, conversely, reaching Ed-Norton-in-Fight-Club status, you may want to check out our handy guide to the best snacks for a good night's sleep — and maybe even see a specialist. No matter your “right” number of hours per night, your sleep and your health are inextricably linked.