A series of studies suggest that sleeping for more than eight hours a night is linked to an increased death rate.
According to the BBC, University of Warwick professor of cardiovascular medicine and epidemiology Franco Cappuccio arrived at this conclusion after examining 16 studies that took place over the past 10 years.
The data contained reports from over a million people regarding how much they slept each night.
All participants were put into three groups based on these numbers: those who slept six hours a night, those who slept between six and eight hours and those who slept for more than eight hours.
Professor Cappuccio then compared how many people from each group had died since the studies were conducted.
The mortality rate of the first group was 12 percent higher than the second group.
But it was those who slept more than eight hours who were most likely to die.
That group had a 30 percent higher mortality rate than those who slept between six and eight hours.
This makes sleeping more than eight hours a night just as dangerous as drinking an excessive amount of alcohol on a daily basis, the BBC reports.
It isn't clear what caused members of the third group to die, but Cappuccio inferred that some of them might have been sleeping for so long as the result of an illness.
The medical conditions may not have initially shown any other symptoms except for the increased sleep, so the deceased couldn't discover them until it was too late.
Their deaths, therefore, would not have been caused by sleep but by their conditions.
Professor Shawn Youngstedt of Arizona State University, however, believes too much sleep can be directly attributed to ill health.
He once asked 14 young adults to sleep for two more hours than usual each night for three weeks.
Youngstedt said the new sleeping schedule caused "increases in depressed mood" as well as "increases in inflammation" and back aches.
This led him to suspect the extra two hours of sleep made participants significantly less active and thus more at risk for health problems.
The professor's current study will explore the effects of subtracting an hour from the sleep schedules of adults who typically spend six to eight or more hours in bed each night.
Citations: Why a long nights sleep may be bad for you (BBC)