Chicago—Research suggests that the risk of stroke is elevated in women who have more—not less—sleep. Women who slept ≥10 hours per night had a 63% increased risk of stroke compared with those who slept <7 hours per night in a substudy of the Nurses’ Health Study reported at a poster session at the AHA meeting.
The observational substudy to examine the relationship between sleep and stroke was initiated in 1986 when 69,794 participants were 40 to 65 years of age; the study ended 20 years later, when participants were 60 to 85 years of age.
Previous studies showed that shorter sleep duration was associated with increased risk of diabetes, coronary heart disease, and cardiovascular and all-cause mortality. The authors of the present study were surprised that they did not find a similar association between shorter sleep duration and stroke.
“We expected to find a U-shaped curve, with risk of stroke elevated by low sleep levels as well as by high sleep levels. We don’t know the reasons behind this association, but we plan to study the data further and try to identify potential mechanisms,” said Alan Flint, MD, research scientist at Harvard School of Public Health in Boston, Massachusetts.
At baseline (in 1986), participants answered detailed questionnaires on medical history, dietary intake, lifestyle, and demographics. They were asked to self-report hours of sleep, as assessed by hours of sleep per a 24-hour period.
Baseline demographic characteristics were similar among groups stratified for hours of sleep per day. Mean age at baseline was about 52 years, mean body mass index was 26 kg/m2, and about 22% were current smokers.
At 20 years of follow-up, 2303 incidents of stroke were documented. In an age-adjusted analysis, compared with participants who had 7 hours of sleep per night (relative risk [RR], 1.0), those who slept ≥10 hours per night were more than twice as likely to have a stroke (RR, 2.14; 95% confidence interval [CI], 1.45-3.15).
A multivariate analysis adjusting for confounding factors found that those who slept ≥10 hours a night were 63% more likely to have had a stroke versus those who slept 7 hours a night (RR, 1.63; 95% CI, 1.11-2.41).
Dr. Flint and coauthors plan to review the data over time. “We want to see if the sleeping patterns of these participants changed over time. Were they always long sleepers, or did they sleep more as they aged? We are also interested in potential mechanisms by which longer sleep duration might be implicated in stroke. These data have implications for stroke risk assessment in clinical practice and epidemiologic studies,” he said.