“Too much sleep could kill you,” is the baseless and needlessly alarmist headline on the front cover of today’s Daily Express.
The study it is reporting on actually showed that people who sleep for more than eight hours a night had a 46% increased risk of stroke over the following 10 years, compared with people sleeping six to eight hours.
While these results certainly warrant further investigation, it does not show that the increased sleep caused strokes, let alone death.
The researchers assessed the usual sleep patterns of nearly 10,000 adults in 1998 and again in 2002, looking for associations between the amount of sleep and the number of people having a stroke over the next 10 years.
They also pooled the results from similar studies. These also showed a 45% increased risk for people who sleep more than eight hours.
When the results were analysed by sex, the link was statistically significant for women, but not men. This wasn’t made clear in the UK media coverage. Women’s risk was 80% higher, which is almost double the 46% risk when the sexes were combined.
The study took into account cardiovascular risk factors such as high blood pressure and cholesterol, but not other illnesses. Without accounting for other illnesses, it is not clear what association the length of sleep has with risk of stroke from these studies. As that widely used, though valid, scientific cliché goes: “further research is needed”.