Getting too much or too little sleep was tied to stroke risk differently depending on race and sex. For black men, less sleep was associated with a decreased risk of stroke. For white men, more sleep was associated with an increased risk of stroke. These are the findings of a prospective cohort study published online in Neurology on October 3.
Stroke is the third most common cause of death in the United States; worldwide it's the leading cause of death and disability. Previous research has indicated that both too much and too little sleep are associated with stroke, and the risk may differ based on factors such as age, sex, and race.
To examine the relationship between reported sleep duration and stroke, and whether age, sex, and race affect the association, researchers evaluated 16,733 people from the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study, a US population-based cohort of black and white adults, aged 45 and older (mean age 64; 37 percent black) who had no history of stroke or sleep apnea.
Between 2008 and 2010, at the start of the study, the team asked participants how many hours of sleep they got on work days and non-work days. Approximately 10 percent were classified as short sleepers (less than 6 hours) and 6.8 percent as long sleepers (9 or more hours). Black adults made up 60 percent of short sleepers and 29.7 percent of long sleepers.
Participants were also asked to complete a questionnaire that provided information on snoring, daytime sleepiness, obesity, and a history of high blood pressure.
Throughout 6.1 years of follow-up, 460 strokes occurred among 172 blacks and 288 whites.
The researchers found that middle-aged or older black adults, particularly black men, who slept less than six hours a night were about 80 percent less likely to have a stroke than average sleepers. Meanwhile, white men who slept nine hours or more had about a 70 percent higher risk of stroke than average sleepers. No differences in stroke risk by sleep duration were observed among black or white women.
The authors acknowledged that the correlation of less sleep and a reduced risk for stroke in black men is "perplexing and conflicts with other studies." Based on their findings, the researchers hypothesized that the short sleepers in their study perhaps were more likely to be employed full time, and therefore more physically active, which may reduce certain risk factors, including obesity, high blood pressure, and high blood cholesterol levels—all of which are exacerbated by a sedentary lifestyle.
The findings about too much sleep and an increased stroke risk among white men adds to the existing evidence. The results about less sleep and a decreased stroke risk among black men is unexpected. Previous research suggested black adults are more likely to experience extremes in sleep duration and greater incidence of stroke.
The researchers commented that while they adjusted for the risk of snoring, they could not rule out undiagnosed sleep apnea as a factor that affects sleep duration.
They suggested that future research should include sleep studies with repeated overnight polysomnography, which can help diagnose a variety of sleep disorders, and wrist actigraphy, which can help monitor rest/activity cycles, to potentially rule out factors such as insomnia that can affect sleep duration.