We all know there are risks associated with getting too little sleep. Chronic lack of sleep is linked to a higher risk of obesity, heart disease, depression, and even early death. Well, it turns out, chronic oversleeping carries the same risks.
In 2016, a study in the International Journal of Cardiology delved into the sleep habits of nearly 400,000 Taiwanese adults over seven years. It found that when compared to people who slept six to eight hours per night, those who slept less than four hours per night experienced an increase of dying from heart disease of 34 percent. Those who slept more than eight hours per night? Nearly identical—their risk increased by 35 percent. Likewise, a 2015 study in Neurology found that people who slept more than eight hours a night experienced a higher risk of stroke, and a 2009 study in Sleep Medicine found the same thing for type II diabetes risk.
Related: Segmented Sleep Used To Be The Norm
But hold on, you might say. These are just correlations—what if it's a person's lousy health that leads to oversleeping, and not the other way around? Excellent point. That's why in 2014, a team of researchers studied the genetics behind these sleep-based health effects with nearly 900 pairs of twins for a study published in the journal Sleep. By using statistical models that examined genetic interactions, they were able to figure out how much a health issue like depression was influenced by genetics—that is, how much it was inherited and how much it was due to a person's environment—and whether sleep had an effect on that heritability. They found that while depressive symptoms had a heritability of about 27 percent in people who got around seven to nine hours of sleep per night, for those who got less than seven or more than nine, the heritability hovered around 50 percent. That's right: under- and oversleeping actually messes with your DNA.