A systematic review and meta-analysis from researchers at the University of Warwick looked at sleep duration and how that impacts life expectancy.
Sleep duration was assessed by questionnaire and outcomes were determined by death certificates. Overall, they found a link between long durations of sleep and the risk of death. Long durations of sleep was determined as more than eight hours of sleep per night.
The data concluded that those who slept for more than eight-and-a-half hours were at an increased risk of 15 percent of experiencing mortality hazards.