He sleeps. She sleeps. They sleep differently.
Women tend to have more deep sleep and awaken fewer times during the night than men do. They also weather some of the effects of a lack of sleep better than men, according to recent studies. Still, men overall say they are more satisfied with the amount and quality of their shut-eye than are women.
Getting enough sleep is an important factor in maintaining overall health. Scientists are increasingly focusing on gender differences in sleep, seeking clues about why women are more likely to suffer insomnia, for instance. Some researchers suggest that differences in sleep patterns could help explain why women live longer than men.
"Women on average have longer sleep than men; women on average are healthier than men. It could be that those are related," said Daniel J. Buysse, a professor of psychiatry and clinical and translational science at the University of Pittsburgh. Sleep difficulties have been linked in many studies with chronic conditions like cardiovascular disease and diabetes.
Most people regularly sleep with a partner, and some research has shown that people wake up more and have less deep sleep when they sleep with another person. Still, people generally say they are more satisfied with their sleep when they are with a loved one.
"There are objective costs to the physical presence of someone else in the bed," said Wendy M. Troxel, an assistant professor at the University of Pittsburgh and a leading researcher on relationships and sleep. But "the safety and security we derive from our social relationships trumps the cost," she said.
Men and women have different body clocks. Men's average "circadian period" was 24 hours, 11 minutes—six minutes longer than for women, according to a study presented at the American Academy of Sleep Medicine's annual meeting in June in Minneapolis. Although six minutes doesn't seem like a big deal, the effects can compound day after day. Researchers determined circadian period by measuring core body temperature and levels of the hormone melatonin.
During the study, which involved 157 healthy people, more men had circadian periods longer than 24 hours and therefore were predisposed to want to go to bed later and get up later each day—classic behavior of so-called night owls. By contrast, twice as many women as men had body clocks shorter than 24 hours and therefore wanted to go to bed earlier and get up earlier.
"That may make it more difficult to stay asleep at the end of the night," contributing to insomnia in women, said Jeanne F. Duffy, associate professor of medicine at Harvard Medical School in Boston and the lead author of the study.
For both sexes, a circadian period that is out of sync with the 24-hour clock can result in sleep deprivation as the week goes on. People with short biological clocks may want to increase exposure to light at night and eliminate it in the morning. Night owls should reduce light exposure before bedtime and get bright light in the morning. Trying to catch up on sleep on the weekends can just push one's biological clock further out of whack.