People who sleep for more than eight hours a day have an increased risk of stroke, according to a study by the University of Cambridge - and this risk doubles for older people who persistently sleep longer than average. However, the researchers say it is unclear why this association exists and call for further research to explore the link. 
 
 Previous studies have already suggested a possible association between sleep and risk of stroke, but today's study, published in the journal Neurology, 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. 
 
 Researchers from the Department of Public Health and Primary Care at the University of Cambridge followed just under 10,000 people aged 42-81 years of age from the European Prospective Investigation into Cancer (EPIC)-Norfolk cohort over 9.5 years. During 1998-2000 and then again four years later, they asked the cohort how many hours on average they slept in a day and whether they generally slept well. 
 
 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. 
 
 Over the almost ten year period of the study, 346 participants suffered a stroke, either non-fatal or fatal stroke. After adjusting for various factors including age and sex, the researchers found that people who slept longer than eight hours a day were at a 46% greater risk of stroke than average. People who slept less than six hours a day were at an 18% increased risk, but the small number of people falling in this category meant the association was not statistically significant. 
 
 Participants who reported persistently long sleep - in other words, they reported sleeping over eight hours when asked at both points of the study - were at 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 - their risk was close to four times that of people who maintained an average sleep duration. 
 
 In addition to studying the EPIC-Norfolk cohort, the researchers carried out a study of combined data from 11 other studies related to identify the association between sleep duration and patterns of stroke risk. Their final analysis, including 560,000 participants from seven countries, supported the findings from the EPIC-Norfolk cohort study. 
 
 Yue Leng, PhD candidate at the University of Cambridge, says: "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." 
 
 While older people have less work and fewer social demands and therefore often have the option of sleeping longer, previous research has shown that in fact, they tend to sleep on average for shorter periods. 
 
 The researchers say it is unclear yet why the link between sleep and stroke risk should exist. Lack of sleep has been linked with factors such as disrupted metabolism and raised levels of the 'stress hormone' cortisol, all of which may lead to higher blood pressure and increased stroke risk. However, the current study suggests that the association between longer sleep duration and higher risk of stroke was independent of normal risk factors for cardiovascular disease. 
 
 Professor Kay-Tee Khaw, senior author on the 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." 
 
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 The study was supported by the Medical Research Council and Cancer Research UK. ||||| Methods: The prospective 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. For the meta-analysis, we searched Ovid Medline, EMBASE, and the Cochrane Library for prospective studies published until May 2014, and pooled effect estimates using a weighted random-effect model. 
 
 Results: After 9.5 years of follow-up, 346 cases of stroke occurred. Long sleep was significantly associated with an increased risk of stroke (hazard ratio [HR] = 1.46 [95% confidence interval (CI) 1.08, 1.98]) after adjustment for all covariates. The association remained robust among those without preexisting diseases and those who reported sleeping well. The association for short sleep was smaller (and not statistically significant) (HR = 1.18 [95% CI 0.91, 1.53]). There was a higher stroke risk among those who reported persistently long sleep or a substantial increase in sleep duration over time, compared to those reporting persistently average sleep. These were compatible with the pooled HRs from an updated meta-analysis, which were 1.15 (1.07, 1.24) and 1.45 (1.30, 1.62) for short and long sleep duration, respectively. ||||| There’s no way to diagnose a stroke before it happens, but researchers say they’ve identified a clue to help doctors predict who’s at risk – the amount of sleep they get at night. 
 
 Older adults who said they slept more than eight hours were 46% more likely to suffer strokes in the next decade than adults who slept for six to eight hours, according to an analysis published Wednesday in the journal Neurology. Even worse, the stroke risk for people who went from sleeping less than six hours to sleeping more than eight hours was nearly four times greater than for people who consistently got six to eight hours of ZZZZs. 
 
 The findings may help clarify the fuzzy relationship between sleep and stroke. A variety of studies have considered the issue, but the results have been inconsistent. 
 
 So researchers from the University of Cambridge and the University of Warwick in England looked for answers in a cancer study. They used data on 9,692 people from Norfolk, England, who participated in the European Prospective Investigation of Cancer. All of them were between the ages of 40 and 79 when they enrolled in the study in the 1990s, and they were tracked for an average of 9.5 years. 
 
 Between 1998 and 2000, and again between 2002 and 2004, the study volunteers were asked how many hours they slept at night and whether they tended to sleep well. Researchers also collected a host of demographic and medical information, including their age, education, smoking and drinking habits, body mass index, blood pressure and family history of stroke. 
 
 Among the 9,692 volunteers, 346 suffered at least one stroke during the years they were tracked (including 67 strokes that were fatal). But these strokes weren’t evenly distributed among all of the volunteers. After controlling for other factors that might affect stroke risk, they found that “long” sleepers (those who slept more than eight hours a night) were at significantly higher risk than “average” sleepers (those who slept for six to eight hours a night). 
 
 People deemed “short” sleepers (those who slept for less than six hours at night) also seemed to be more susceptible to a stroke. Their risk was 18% greater than for average sleepers, but the difference was small enough that it could have been due to chance. 
 
 Upon closer inspection, the researchers noticed some intriguing patterns. The relationship between sleep duration and stroke risk was somewhat stronger for women than for men. It was also stronger for strokes that were fatal, according to the study. 
 
 When the study participants were examined according to age, the researchers found that sleeping for more than eight hours a night increased stroke risk only for people who were at least 63 years old. On the flip side, they found that sleeping for less than six hours a night heightened stroke risk for younger people more than for older people. 
 
 Finally, they discovered that “short” sleepers were more at risk for an ischemic stroke (the kind caused by a clot that blocks blood flow to the brain) while “long” sleepers were more at risk for a hemorrhagic stroke (the kind caused by a ruptured blood vessel bleeds into the brain). 
 
 The research team also conducted a meta-analysis that combined their results with those of 11 previously published studies. Altogether, the analysis included nearly 560,000 people from seven countries who suffered a total of more than 8,000 strokes. 
 
 In the meta-analysis, “short” sleep was associated with a 15% increased risk of stroke and “long” sleep was linked with a 45% greater risk. Those results validated their findings, the researchers wrote. 
 
 Still unclear is whether sleeping too much or too little can actually cause a stroke, or whether the biological processes that lead to a stroke also happen to influence sleep. Other studies have linked long sleep times to cardiac problems like atrial fibrillation, atherosclerosis and other conditions that may make a stroke more likely. But scientists will have to conduct experiments to get a better idea of how sleep and strokes are related, the study authors wrote. 
 
 In the meantime, it would behoove doctors to inquire about their patients’ sleep habits – and if their older patients report long sleeping times, they should consider it a warning sign for a stroke, the researchers wrote. 
 
 That conclusion was echoed by a neurologist and a sleep researcher in an editorial that accompanied the study. 
 
 “Long sleep duration could therefore be a harbinger of stoke through its association with potent cardiovascular risk factors,” wrote Dr. Alberto Ramos of the University of Miami’s Miller School of Medicine and James Gangwisch of Columbia University. “Lengthening sleep duration could portend strokes and serve as an early warning sign, suggesting the need for further diagnostic testing or for taking precautionary measures.” 
 
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– Sleeping more than eight hours a night? That may be too much of a good thing, because you're more likely to suffer a stroke, according to a study out of the University of Cambridge. Researchers analyzed the sleep patterns of nearly 10,000 people ages 42 to 81 in the UK, and they report in the journal Neurology that based on nearly a decade of follow-up and 346 reported strokes, older adults who sleep more than eight hours a night are 46% more likely to suffer a stroke than adults who slept six to eight hours. That risk is actually four times greater when people went from sleeping for less than six hours at the beginning of the study to more than 8 as the years passed, per a Eureka Alert press release. The researchers adjusted for several factors, including age and sex, and their findings were strikingly consistent with what they found in a review of the combined data of 11 similar studies spanning 560,000 people in seven countries. But in terms of age and sex, the Los Angeles Times notes the following: The link between the risk and sleep length was a little stronger for women, and the increased stroke risk was only seen in those eight-plus-hours sleepers who were 63 or older. The researchers caution that it remains unclear whether longer sleep duration is a symptom or cause of stroke risk. Says one, "With further research, we may find that excessive sleep proves to be an early indicator of increased stroke risk." (Experts have just revealed how much sleep you should be averaging a night based on your age.)