http://www.independent.co.uk/life-style/health-and-families/health-news/people-who-sleep-more-than-eight-hours-are-more-likely-to-have-a-stroke-research-shows-10070327.html
A study of nearly 10,000 people carried out at the University of Cambridge found that those who took eight hours on average had a 46 per cent higher than average risk of having a stroke.
Adults tend to need between six and nine hours sleep to feel well-rested, but oversleeping has previously been linked with health problems such as diabetes or obesity.