Researchers from the University of Warwick and University College London have found that while a lack of sleep doubles a person's risk of death from cardiovascular diseases, too much of sleep can also have the same mortality effect from predominantly non-cardiovascular diseases.
Professor Francesco Cappuccio from the University of Warwick's Warwick Medical School, who presented the findings to the British Sleep Society on Monday, said the study involved the analysis of data on the mortality rates and sleep patterns on 10,308 civil servants at two points in their life (1985-88 and then in 1992-93).
He said that the effect that changes in sleep patterns over five years had on mortality rates 11-17 years later were isolated by adjusting other possible factors—such as age, sex, marital status, employment grade, smoking status, physical activity, alcohol consumption, self-rated health, body mass index, blood pressure, cholesterol, other physical illness etc.
Seven hours of sleep per night was taken to be the baseline during the study, he added. Professor Cappuccio said that the participants who had cut 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 in particular by 2004.
He further said that individuals who showed an increase in sleep duration to eight hours or more a night were more than twice as likely to die as those who had not changed their habit, though predominantly from non-cardiovascular diseases.
"Short sleep has been shown to be a risk factor for weight gain, hypertension and Type 2 diabetes sometimes leading to mortality, but in contrast to the short sleep-mortality association it appears that no potential mechanisms by which long sleep could be associated with increased mortality have yet been investigated. Some candidate causes for this include depression, low socio-economic status and cancer-related fatigue," said Professor Cappuccio
"In terms of prevention, our findings indicate that consistently sleeping around 7 hours per night is optimal for health and a sustained reduction may predispose to ill-health," he added.
The study will be published in the journal Sleep.