Sleeping too much is most likely bad for you. A number of studies have described mental health problems and chronic conditions related to sleeping too much.
Sleeping too much may increase your risk of dying a premature death. A group of scientists did a meta-analysis of sixteen different studies and found that sleeping more than eight hours a night can raise your risk of a premature death by 1.3 times.
That may because sleeping has been linked to a whole range of chronic diseases. A study and meta-analysis published in the American Journal of Neurology found that prolonged sleep significantly increased your risk of having a stroke - 1.4 times in the study and 1.45 times in the meta-analysis. A cross-sectional study that surveyed 50,000 adults in the United States found a link between oversleeping and a higher risk of coronary heart disease. The National Health Service in the U.K. published an easy-to-read explanation of the study's findings and limitations; while the study isn't perfect, there's a growing body of evidence that such a connection may exist. Another study done in Quebec - this one much smaller - found that too much or too little sleep increased the risk of insulin resistance or diabetes by a factor of two.
Sleeping doesn't just increase your risk of chronic conditions. It can also have an effect on your mental health. A Harvard published in the Journal of American Geriatrics looked at sleep duration in older women and found that those who slept more performed worse on various measures of memory and cognition. The effect appeared in those who slept nine hours or more a night. The effect was borne out by another paper, this one published in the Journal of American Psychiatry: they found a statistically significant decline in the cognitive function of men and women who slept more.
This may be because the physical conditions that sleeping too much is linked to, such as heart disease or stroke, restrict the flow of blood to the brain. It may be because too much sleep scars the brain with deposits of beta-amyloid, which interferes with memory; that much has been demonstrated in mice.
Whatever the cause, there seems to be a connection between too much sleep and the health of the brain. A 2014 study looking at the heritability of depression in twins found that sleeping too much can up your risk of becoming depressed. Those who slept between seven and nine hours a night ran a heritability of depression around one in three; those who slept too little or too much upped the heritability to around one in two. That suggests that too much sleep may open up epigenetic pathways that lead to depression.
Possible short-term side effects
Possible long-term side effects
- premature death
- heart disease
- reduced memory and cognition
- getting 7-9 hours of sleep