Researchers from the Norwegian University of Science and Technology collected information from 400,000 Taiwanese adults, aged 20 years and older, who had medical check-ups between 1994 and 2011. The participants were asked how long they slept each night, from zero to more than eight hours.

In a follow-up, 711 of the volunteers had died from cardiovascular disease, leading the researchers to conclude that those who reported sleeping eight hours or more were 35 percent more likely to die from the disease, compared to those who slept six to eight hours a night. Those who slept less than four hours were 34 percent more likely die from the condition.

Although previous studies had shown that a lack of sleep was linked to stress, increased blood pressure and the secretion of adrenaline – all of which are factors of an increased risk of heart disease – the effects of too much sleep on heart disease came as a surprise.