Researchers from the University of Warwick and University College London conducted a large study in which they linked duration of sleep and mortality. They found that lack of sleep doubles the risk of death from heart disease but also the harmful effects of sleeping too much.

The study looked at the sleeping patterns of participants aged 35-55 and took into account various factors such as age, sex, marital status, employment grade, smoking status, physical activity, alcohol consumption, self-rated health, body mass index, blood pressure, cholesterol, and other possible physical ailments. They adjusted for these factors and then looked at what effects could changes in sleeping patterns have on mortality rates a decade later.

They found that those people who slept for less than seven hours had a 1.7-fold increased risk of death from all causes and increased chances for suffering from cardiovascular problems.

Too much sleep also increased mortality but it was from non-cardiovascular diseases. Longer sleeping was associated with depression, low socioeconomic status and cancer-related fatigue but the factors by which long sleep could be associated with increased mortality have not been found yet.

Researchers advise that regular seven hour sleep is optimal for health and could help prevent many health ailments.