A new epidemiological study from a team of Chinese researchers is suggesting sleeping more than nine hours a night, and/or taking long midday naps, can significantly increase a person’s risk of stroke. The research does not highlight a particular causal connection between stroke and too much sleep but does add to a growing body of work finding deleterious health effects from excessive sleep.
The research involved analyzing data from a longitudinal research project called the Dongfeng-Tongji cohort study. This study is following a cohort of over 30,000 people, with an average age of 62 at the time of enrollment, and has been running for almost 10 years.
The new article, published in the journal Neurology, examines the relationship between sleep patterns and incidence of stroke. Across six years of follow-up, the cohort reported around 1,500 cases of stroke.
The study identified a reasonably striking correlation linking long sleeping duration with increased rates of stroke. People reporting regular midday naps lasting more than 90 minutes were 25 percent more likely to suffer from a stroke, compared to those reporting daily naps of 60 minutes or less.
Sleeping more than nine hours every night also correlated with a 23 percent increase in stroke risk. This increase in the incidence of stroke was not seen in those sleeping less than nine hours a night. Interestingly, even those reporting nightly sleep duration of less than seven hours did not display higher incidence of stroke.
Combining long midday naps with excessive nightly sleep resulted in the highest stroke risk, with those individuals displaying 85 percent higher rates of stroke than short nappers with average nightly sleep patterns.
At this stage it is unclear if there is a causal link between excessive sleep and stroke. The researchers are clear in pointing out the study only identifies an association. Xiaomin Zhang, an author on the new study from Huazhong University of Science and Technology in Wuhan, China, suggests while excessive sleep may hypothetically result in negative physiological outcomes, it is just as reasonable to consider these longer sleep patterns to be symptoms of other unhealthy lifestyle behaviors that may be increasing a person’s stroke risk.
"More research is needed to understand how taking long naps and sleeping longer hours at night may be tied to an increased risk of stroke, but previous studies have shown that long nappers and sleepers have unfavorable changes in their cholesterol levels and increased waist circumferences, both of which are risk factors for stroke," says Zhang. "In addition, long napping and sleeping may suggest an overall inactive lifestyle, which is also related to increased risk of stroke."
The general limitation most of these large epidemiological sleep studies face is they primary rely on self-reported questionnaire data, often only recorded at a single point in time. Sleep quality and duration can be inconsistent so it is certainly difficult to ascertain long-term trends from subjective self-reporting.
However, as researchers inevitably gather more and more data, certain trends can become apparent. The results of a massive sleep study published last year, tracking over 10,000 people, discovered an intriguing correlation between cognitive deficits and irregular sleep duration. That study found individuals who reported sleeping more than eight hours each night performed as poorly on several cognitive tests as those sleeping less than six hours each night. The optimal sleep duration recommended in that study was between seven and eight hours each night.
It is not unreasonable to assume excessive sleep is merely a symptom, and not a cause, of a condition that could increase a person’s risk for stroke. But, at the very least, the new research can point to excessive sleep patterns as a valid warning sign of increased stroke risk in middle-aged and older adults.
The new research was published in the journal Neurology.
Source: American Academy of Neurology