A new study has found lack of sleep can more than double the risk of death from cardiovascular disease, but increase the sleep, and there comes a point when too much sleep can also more than double the risk of death.

The researchers, at the Britain's University of Warwick and University College London, based their findings on a study of sleep patterns of more than 10,000 civil servants. Taking those who had not made any change in their sleeping habits between 1985-88 and 1992-93 as their baseline, they were able to identify what difference having reduced the amount of sleep made to mortality rates by 2004. The researchers used a baseline of seven hours of sleep a night as the optimal amount of rest.

Those who had cut back their sleeping from seven to five hours or less faced a 1.7-fold increased risk in mortality from all causes, and twice the increased risk of death from a cardiovascular problem. ShortLack of sleep is also a risk factor for weight gain, hypertension and type two diabetes sometimes leading to mortality, the researchers said.

The researchers also found those who increased their sleep duration to eight hours or more a night were more than twice as likely to die during the period as those who had not changed their habit, though predominantly from non-cardiovascular diseases. Some candidate causes for this include depression, and cancer-related fatigue, the researchers said.