Pan A, De Silva DA, Yuan JM, and Koh WP. Sleep Duration and Risk of Stroke Mortality Among Chinese Adults:Singapore Chinese Health Study. Stroke. 2014
In their paper, Pan et. al. take a close look at the association between sleep duration and stroke mortality in Chinese adults. They’re interested in this topic for several reasons: short and long sleep durations have been associated with an increased risk of coronary heart disease mortality among Singaporean Chinese; the association between sleep and stroke has not been studied in the Chinese population; data are not consistent regarding the association between long and short sleep durations and the risk of stroke.
They used data from the Singapore Chinese Health Study which enrolled patients aged 45-74 years between 1993-1998. Data points gathered included smoking status, exercise habits, diabetes, hypertension, cardiac disease, and average nightly sleep duration. Deaths were identified through their Singapore Registry of Births and Deaths almost through the entirety of 2011. They found that sleeping too much or too little (≤ 5 hours or ≥ 9 hours) was associated with an increased risk of stroke mortality as compared to their reference point of sleeping 7 hours/day. This association was observed only in ischemic or unspecified stroke and not with hemorrhagic stroke.
A couple of thoughts: we don’t know the NIHSS of the strokes included in this study. Since the biggest predictor of stroke-related death is stroke severity, the NIHSS is a necessary part in understanding the suggested association between sleep duration and stroke mortality. The second biggest predictor of stroke-related death is age. Long and short durations of sleep were associated with an increased risk of stroke mortality but when the analysis was adjusted for age, the relationship was slightly attenuated. So, is sleep duration a residual confounding factor of stroke mortality? We can easily document and categorize age but it’s much harder to accurately do this for sleep duration. If we came up with a better, more exact way to classify sleep duration, perhaps the relationship that the authors found would disappear. Very interesting article although it’s very difficult to discuss issues surrounding stroke mortality without discussing the severity of the stroke.