Sleeping over eight hours raises risk by 46%
Sleep is increasingly suggested as a predictor of cardiovascular events, and stroke is an outcome of particular interest. A study conducted last year had found an association between sleep duration and risk of stroke mortality in a large sample of Chinese adults. It is unclear whether his association is applicable to nonfatal stroke, and if this could be modified by sleep quality.
In this new study researchers from the Department of Public Health and Primary Care, University of Cambridge; and the Division of Mental Health & Wellbeing University of Warwick examined the association between sleep duration and stroke incidence in a British population and to synthesize our findings with published results through a meta-analysis.
This study included 9,692 stroke-free participants aged 42–81 years from the European Prospective Investigation into Cancer–Norfolk cohort . Participants reported sleep duration in 1998–2000 and 2002–2004, and all stroke cases were recorded until March 31, 2009. The team searched OvidMedline, EMBASE, and the Cochrane Library for prospective studies published up to May 2014 for the meta-analysis.
Almost seven out of ten participants reported sleeping between six and eight hours a day, whilst one in ten reported sleeping for over eight hours a day. Participants who slept for less than six hours or more than eight hours were more likely to be older, women and less active, to have major depressive disorder, and to be taking antihypertensive drugs. No significant association was found between sleep duration, body mass index, systolic blood pressure, preexisting diabetes or myocardial infarction (heart attack).
After 9.5 years of follow-up, 346 cases of fatal or nonfatal stroke. There were 67 fatal strokes, 300 hospital admissions with 21 participants being admitted to hospital before subsequent death.
After adjusting for various factors including age and sex, participants with short sleep duration (less than six hours a day) had an 18 percent increased risk for stroke (not statistically significant). Participants with long sleep duration (over eight hours a day) had a 46 percent increased risk for stroke.
The participants who reported persistently long sleep duration) over eight hours of sleep) had at least double the risk of stroke compared to those with persistently average sleep duration (between six and eight hours a day). This risk was even greater for those whose reported sleep increased from short to long over the four years had a stroke risk of almost four times greater compared to those who maintained an average sleep duration.
Yue Leng, a PhD candidate, Department of Public Health and Primary Care at the University of Cambridge, commented “It’s apparent both from our own participants and the wealth of international data that there’s a link between sleeping longer than average and a greater risk of stroke. What is far less clear, however, is the direction of this link, whether longer sleep is a symptom, an early marker or a cause of cardiovascular problems.”
“This prospective study and meta-analysis suggested a significant increase in stroke risk among long
sleepers and a modest increase among short sleepers. Persistently long sleep or marked increase in sleep duration were associated with subsequent risk of stroke. The underlying mechanism needs further investigation. Prolonged sleep might be a useful marker of increased stroke risk in older people, andshould be tested further for its utility in clinical practice,” write the researchers.
Professor Kay-Tee Khaw, MD, Professor of Clinical Gerontology and Fellow of Gonville and Caius College, Cambridge, principal investigator in the European Prospective Investigation in Cancer in Norfolk and senior author of this study adds; “We need to understand the reasons behind the link between sleep and stroke risk. What is happening in the body that causes this link? With further research, we may find that excessive sleep proves to be an early indicator of increased stroke risk, particularly among older people.”
This is the first to provide detailed information about the British population and to examine the relationship between a change in sleep duration over time and subsequent stroke risk.
The study was supported by the Medical Research Council and Cancer Research UK.
Sleep duration and risk of fatal and nonfatal stroke: A prospective study and meta-analysis.Neurology, 2015 DOI: 10.1212/WNL.0000000000001371
University of Cambridge News