Are you concerned because you didn't get your full eight hours of sleep last night? Last month? Last year? Don't worry. As long as you're sleeping at least five or six hours a night, you may be doing just fine. New research suggests that women who sleep less may live longer than their well-rested counterparts – and as an added bonus, reduce their risk of stroke.
Stroke and Sleep
Research presented November 13 at the American Heart Association annual meeting suggests that women who get more than 10 hours of sleep each night may be at increased risk of stroke, compared to women who slept an average of 7 hours per night.
The research team, led by Alan Flint, M.D., of the Harvard School of Public Health, studied nearly 70,000 women nurses ages 40 to 65 from 1986 to 2006. Investigators asked the women to report the total hours they slept each night, which ranged from less than five to 11 or more. They also collected information from the the women about lifestyle factors that might affect their risk of stroke, such as how much alcohol they drank, fruit and vegetable consumption, physical activity, and whether or not they smoked. They recorded the women's weight and whether they had diabetes or high blood pressure, all of which can affect stroke risk.
Twenty years later, a total of 2,303 strokes had been reported. When the researchers looked at which women were having the strokes, they found that women who slept seven hours a night were had the lowest average risk of stroke. Women who slept 10 or more hours each night were 63 percent more likely to experience a stroke compared to women in the seven-hour group. Women who slept six or fewer, or from eight to nine hours a night, had insignificant increases in stroke risk.
Researchers weren't able to say why women who slept longer hours were at higher risk of stroke. Flint noted, "We'd like to update [the study] and get an idea of whether a pattern of sleep over a lifetime that accounts for the risk, or whether there are other factors that account for that, like clinical depression, jobs, family, or other interaction with that risk."
Flint also said he was performing similar research in a large group of men.
Sleep Less, Live Longer
Flint's research contributes to a growing body of research that suggests that a little less than the eight-hour sleep standard might not be all that bad for women's health. In September 2010, a team led by Daniel F. Kripke, MD, professor emeritus of psychiatry at the University of California San Diego School of Medicine, reported that women who slept between 5.0 and 6.5 hours each night were likely to live longer than those who slept more or less.
Kripke and colleagues based their conclusions on women who had participated in a study of sleep patterns 14 years ago. Between 1995 and 1999, as part of the Women's Health Initiative, Kripke's team had monitored the sleep habits of 459 women ranging in age from 50 to 81. All of the women lived in San Diego.
Fourteen years later, Kripke and his colleagues tracked down 444 of the original participants, including 86 women who had died. They compared the data they had gathered about the women's sleep habits with their status (alive or dead) or, if they had died, how old they had been when they died.
Most sleep studies use questionnaires to determine people’s sleep habits. These studies had suggested that people who slept 6.5 to 7.5 hours per night were likely to live longest. But Kripke's team used wrist activity monitors instead of self-reported data to record how long people slept. Using these measurements, they found that women who slept a little less – 5 to 6.5 hours – often lived the longest. Less than five hours is probably not enough, and eight hours is probably too much.
“The surprise was that when sleep was measured objectively, the best survival was observed among women who slept five to 6.5 hours,” Kripke said. “Women who slept less than five hours a night or more than 6.5 hours were less likely to be alive at the 14-year follow-up.”
The findings were published online in the September 25 issue of the journal Sleep Medicine. Kripke said the study should lay to rest some people’s fears that they’re not getting enough sleep. “This means that women who sleep as little as five to six-and-a-half hours have nothing to worry about since that amount of sleep is evidently consistent with excellent survival. That is actually about the average measured sleep duration for San Diego women.”
Researchers also found that obstructive sleep apnea (pauses in breathing during sleep) in women aged 60 years or more did not increase their risk of death. This finding was in sharp contrast to sleep apnea in younger women. Kripke noted that for women under 60, sleep apnea may be associated with increased risk of death, “it does not seem to carry a risk in the older age group, particularly for women.”
Flint, A, Hu, F, Manson, J, & Rexrode, K. (2011). Abstract 13072: A Prospective Study of Sleep Duration and Risk of Incident Stroke in Women. Circulation 122: A13072. Available at: http://circ.ahajournals.org/cgi/content/meeting_abstract/122/21_MeetingAbstracts/A13072?maxtoshow=&hits=10&RESULTFORMAT=&fulltext=Flint+Stroke&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT
Kripke, D.F, Langer, R.D., Elliott, J.A., Klauber, M.R., & Rex, K.M. (2011). Mortality related to actigraphic long and short sleep, Sleep Medicine, (12:1), pp. 28-33.DOI: 10.1016/j.sleep.2010.04.016. Available at: http://www.sciencedirect.com/science/article/B6W6N-513F5DM-1/2/3fd5d3ca1af9497a804be4ac2a5097b2
Photo by Alan Cleaver