The importance of getting enough sleep has been emphasized by hundreds of studies in recent years, and we've covered the topic many times on this blog.
Inadequate sleep has been linked to obesity, heart disease, diabetes, high blood pressure, and other health problems. And, according to the National Highway Traffic Safety Administration, up to 72,000 car acidents and 6,000 deaths occur each year due to sleep-deprived drivers.
But what about too much sleep? Could that be bad for you, too? According to a new study, the answer may be yes.
More sleep, more strokes?
Researchers publishing in the December 11, 2019, online issue of Neurology describe an analysis of stroke risk among nearly 32,000 adults with an average age of 62. The study's authors compared rates of stroke with study subjects' self-reported sleep habits.
Their findings were surprising (at least to me) and included:
- Those who reported sleeping nine or more hours each night had a 23% higher risk of stroke than those sleeping less than eight hours each night.
- Stroke risk was 25% higher among those who took midday naps for at least 90 minutes compared with those napping for less than 30 minutes.
Poor sleep quality was also linked to higher stroke risk
Combinations of these factors had an even more dramatic effect on stroke risk, including an 85% higher risk among those who slept at least nine hours each night and also took midday naps for at least 90 minutes. Similarly, an 82% higher stroke risk was observed among those who slept longer at night and also reported poor sleep quality.
Does this mean too much sleep causes strokes?
If you are a person who sleeps more than nine hours each night, takes long midday naps, and feels your sleep quality is poor, these results may be troubling. But before trying to change your sleep habits, keep in mind this study did not conclude that more sleep actually causes strokes.
This study found an association between stroke risk and longer sleep, longer midday napping, or poor sleep quality. But an association is not the same as causation. Rather than longer sleep duration causing strokes, there are other possible explanations for the findings. For example, people who sleep more at night or nap more during the day may have other risk factors for stroke, such as:
- A higher incidence of depression. Excessive sleeping or poor sleep quality may be symptoms of depression, and prior studies have noted higher stroke rates among depressed individuals.
- A more sedentary lifestyle. Those who are not active may sleep or nap more and also have more cardiovascular risk factors (such as smoking or hypertension) than those who exercise regularly. Past research has noted less favorable cholesterol levels and larger waist circumference among long sleepers and nappers.
- Sleep apnea. Longer sleep duration, more napping, and poor-quality sleep may be more common among people with sleep apnea, a condition linked to an increased risk of stroke. This new study did not ask subjects about sleep disorders such as sleep apnea.
In addition, this study had weaknesses that could call its findings into question or limit its applicability. These include reliance on self-reported sleep habits and quality, and inclusion only of middle-aged and older Chinese adults without prior cancer or cardiovascular disease; the results might have been quite different if others were included in the study.
The bottom line
Sleep is a mysterious thing. It's often unclear why some people sleep more or less than others, or why certain sleep disorders (such as insomnia or sleep apnea) affect so many people while sparing others. At a time when there's so much media emphasis on the importance of getting enough sleep, this new study raises the possibility that more sleep may not always be a good thing. Still, we'll need additional research on the question of whether more sleep is hazardous before making any firm recommendations to limit sleep duration.