BOSTON – Consistently short sleep duration not only leaves otherwise healthy individuals tired, it also increases their risk of developing stroke, a study has shown.
Previous studies have linked self-reported sleep duration to incident stroke, but none have considered whether sleep-disordered breathing, which itself is associated with adverse cardiovascular outcomes, mediates that risk, said Megan Ruiter, Ph.D., of the University of Alabama at Birmingham. Dr. Ruiter and her colleagues used data from the national, population-based REGARDS (Reasons for Geographic and Racial Differences in Stroke) study to determine whether sleep duration predicts stroke risk among individuals at low risk for sleep apnea or hypopnea.
Funded by the National Institute of Neurological Disorders and Stroke, the ongoing REGARDS study enrolled more than 30,000 black and white volunteers, aged 45 years and older, to track stroke risk and cognitive health.
Based on self-reported stroke symptoms collected at 6-month intervals, Dr. Ruiter and her colleagues identified 5,666 participants who had been followed for up to 3 years without history of stroke, transient ischemic attack, stroke symptoms, or high risk for sleep-disordered breathing according to the Berlin Sleep Questionnaire. The researchers then conducted interval-censored, parametric survival models with exponential distributions to estimate the hazard ratios predicting time from measurement of sleep duration (less than 6 hours, 6-6.9 hours, 7-7.9 hours, 8-8.9 hours, and 9 or more hours) to first stroke symptoms. Data were adjusted for demographic information, cholesterol levels, hypertension, body mass index (BMI), sleep-disordered breathing, depressive symptoms, and anxiety.
"In people with a low risk for obstructive sleep apnea and a BMI in the optimal range of 18.5-24.99 kg/m2, the risk of stroke symptoms was four times higher in those who had fewer than 6 hours of sleep per night, compared with participants in the same BMI range who reported 7-8 hours of sleep per night," Dr. Ruiter reported at the annual meeting of the Associated Professional Sleep Societies. Specifically, the hazard ratio for stroke symptoms among individuals within the normal BMI range who reported fewer than 6 hours of sleep nightly was 2.93, relative to the reference group. "We didn’t find any similar association between short sleep duration and stroke symptoms among overweight and obese individuals," she noted.
The association between shorter periods of sleep and stroke symptoms, including sudden body weakness, numbness, or vision deficits, remained significant after controlling for other known stroke risk factors, Dr. Ruiter said, acknowledging the possibility that "these participants may be late in the development of stroke."
The findings suggest that habitually short sleep duration may independently predispose middle-age adults to develop major stroke risk factors. "We speculate short sleep is precursor to other traditional risk factors and, once these traditional risk factors are present, they may become stronger risk factors than sleep duration alone," Dr. Ruiter hypothesized.
In a separate analysis, the investigators also evaluated the association between stroke symptoms and sleep duration by racial group and found a differential risk, according to Dr. Ruiter. "It is possible that sleep duration might partially explain the relationship between ethnic differences in stroke symptoms. For example, African Americans had a greater prevalence of short sleep and were more likely to have stroke symptoms," she said.
The study is limited by the reliance on self-reporting of stroke symptoms and the potential for recall inaccuracy, Dr. Ruiter said. Further studies are warranted to tease out the specific characteristics of sleep duration that are related to stroke symptoms, she said. For example, "Is it actually sleep fragmentation or one’s perception of sleep and factors that contribute to its quality rather than sleep duration itself?" she proposed. Additionally, "we need to see if sleep duration is related to actual stroke events." Many of these factors, she noted, are modifiable through behavioral treatment.
Dr. Ruiter had no relevant financial conflicts of interest to disclose.