In research presented to the British Sleep Society, Professor Francesco Cappuccio from the University of Warwick's Warwick Medical School showed the results of a study of how sleep patterns affected the mortality of 10,308 civil servants in the "Whitehall II study". Amongst other things the data they used provided information on the mortality rates and sleep patterns on the same group of civil servants at two points in their life (1985-8 and those still alive in 1992-3).
Researchers from the University of Warwick, and University College London, have found that lack of sleep can more than double the risk of death from cardiovascular disease. However they have also found that a point comes when too much sleep can also more than double the risk of death.
The researchers took into account other possible factors such 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. Once they had adjusted for those factors they were able to isolate the effect that changes in sleep patterns over 5 years had on mortality rates 11-17 years later.
Taking those who had not made any change in their sleeping habits between 1985-8 and 1992-3 as their baseline (7 hours per night being the figure normally recommended as an appropriate period of sleep for an adult) they were able to see what difference having reduced the amount of sleep over time made to mortality rates by 2004.
Those who had cut their sleeping from 7h to 5 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.
Professor Francesco Cappuccio from the University of Warwick's Warwick Medical School said to the British Sleep Society:
"Fewer hours sleep and greater levels of sleep disturbance have become widespread in industrialised societies. This change, largely the result of sleep curtailment to create more time for leisure and shift-work, has meant that reports of fatigue, tiredness and excessive daytime sleepiness are more common than a few decades ago. Sleep represents the daily process of physiological restitution and recovery, and lack of sleep has far-reaching effects."
Curiously the researchers also found that too much sleep also increased mortality. They found that those individuals who showed an increase in sleep duration to 8 hours or more a night were more than twice as likely to die as those who had not changed their habit, however, predominantly from non-cardiovascular diseases.
Professor Francesco Cappuccio says:
"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 socioeconomic status and cancer-related fatigue."
"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."