It's long been reported that a lack of sleep can be hazardous to one's health, but so can too much sleep, UK researchers report.

Researchers from the University of Warwick and University College London found that both a lack of sleep and too much sleep can more than double the risk of death in individuals, according to a study of more than 10,308 people.

Professor Francesco Cappuccio from the University of Warwick’s Warwick Medical School, speaking Monday to the British Sleep Society, said researchers studied data on the mortality rates and sleep patterns on the same group of civil servants at two points in their life (1985-1988 and those still alive in 1992-1993).

After taking into consideration age, sex, marital status, employment grade, smoking, physical activity, alcohol consumption, self-rated health, body mass index, blood pressure, cholesterol and other physical illness, researchers were able to isolate the effect that changes in sleep patterns over five years had on mortality rates 11 to 17 years later.

Participants who had cut their sleeping from seven hours to five hours or less a night faced a 1.7-fold increased risk in death from all causes, and twice the increased risk of death from a cardiovascular problem in particular.

But they also found that those individuals who showed an increase in sleep duration to eight hours or more a night were more than twice as likely to die as those who had not changed their habit, however, predominantly from non-cardiovascular diseases.

Some reasons cited for too much sleep included depression, low socioeconomic status and cancer-related fatigue.

“In terms of prevention, our findings indicate that consistently sleeping around seven hours per night is optimal for health, and a sustained reduction may predispose (people) to ill-health,” Cappuccio said in a news release.