Too much sleep could be worse for health than too little

An analysis of pooled data from dozens of studies covering more than 3 million people finds that self-reported sleep duration outside of 7–8 hours each night is linked to a higher risk of death and cardiovascular diseases.

The study — which scientists at Keele University in the United Kingdom led and which is now published in the Journal of the American Heart Association — found a “J-shaped” relationship between duration of sleep and deaths. The same relationship was observed with incidents of cardiovascular illness.

The authors say that their findings suggest that sleeping for more than 7–8 hours “may be associated with a moderate degree of harm” compared with sleeping less.

The J-shaped relationship showed that the size of the risk rose in line with greater duration of sleep. Sleeping for 9 hours, for example, carried a 14 percent higher risk of death, while 10-hour sleeps carried a 30 percent higher risk.

The results also showed that poor-quality sleep was linked to a 44 percent higher risk of coronary heart disease.

“Our study,” says lead study author Dr. Chun Shing Kwok, a clinical lecturer in cardiology at Keele University, “has an important public health impact in that it shows that excessive sleep is a marker of elevated cardiovascular risk.”