A new study found that sleeping more than eight hours increases one's risk of dying early due to a hidden illness that causes oversleeping, according to BBC News.

Researchers at the University of Warwick did a meta-analysis of 16 different studies related to sleeping and health issues. The total number of participants in these studies was over a million, and they were divided into three groups: the short sleepers, who slept less than six hours per night, the medium sleepers, who slept between six and eight hours, and the long sleepers, who slept more than eight hours.

The analysis showed that the short sleepers' risk of dying early was 12 percent higher than that of the medium sleepers. But the long sleepers have a higher risk at 30 percent compared to those who get between six and eight hours of snooze time.

The team continued the study to determine why the long sleepers have a higher risk than the short sleepers. Franco Cappuccio, professor of cardiovascular medicine and epidemiology at the University of Warwick, concluded that this is because those who oversleep usually consume sleeping pills just to doze off, which is really damaging to their overall health.

The researchers coined the underlying reasons for the longer sleep hours as "hidden illness." This hidden illness might be due to depression, back pain, and inflammation. Further study will be conducted to pinpoint the actual cause, according to the researchers.

The findings of the study imply that the healthiest number of sleep hours is between six and eight hours. But what is the most recommended? A sleep expert weighs in.

"Seven hours sleep keeps turning up over and over again," Gregg Jacobs, of the Sleep Disorders Center at the University of Massachusetts Medical School, told BBC News.

According to the U.S. Centers for Disease Control and Prevention (CDC), sleep is increasingly being recognized as a public health issue, as people who suffer from insufficient sleep are often involved in accidents and occupational errors. They are also more likely to suffer from chronic diseases such as hypertension, diabetes, depression, and obesity, as well as from cancer, increased mortality, and reduced quality of life and productivity.