"In couples where one is an early bird and one is the other type, they know it," says Dr. Charmane Eastman, director of the Biological Rhythms Research Lab and professor of psychology at Rush University Medical Center in Chicago. "But sometimes the rhythm differences actually work because it means that each person gets to have time alone."
If you decide to try to re-set your body clock, you'll need to be dedicated, she says. Night owls trying to morph into early risers should seek exposure to light earlier in the morning. Since the most intense light is outside, try waking up at the same time each day and getting outdoors as soon as possible.
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Shifting early birds should avoid bright light in the morning. Aim for darkroom-level bedroom light, stay inside as long as possible, and wear dark sunglasses when finally venturing outdoors.
But here's the kicker—even after a couple of weeks on a new sleep schedule, a one-day lapse will shift the clock right back to its natural state.
"Like going on a diet, it's hard to keep the rhythm there," Eastman warns. Sleep-deprived night owls who really want to give their partners some alert morning time also can try napping in the middle of their normal waking period, she adds.
Ideally, of course, their sweethearts would join them, but midday sex may be the rarest luxury. Research finds that younger couples most often have sex between 10 and 11 p.m., Smolensky reports. Convenience, rather than body clocks, may explain this finding, but he says that studies, including his own, do show natural patterns: For example, people have more sex in fall and winter, when males secrete more testosterone.
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Even if mismatched couples find they can't—or don't want to—change, being aware of and understanding about a partner's rhythm can ease tension. "My best advice for an early bird and a night owl in love is to respect the biology of the other person," says Eastman.