A new UK study suggests that both too much and too little sleep can more than double the risk of death from heart disease.
To be published in the journal SLEEP, the study is the work of scientists from the University of Warwick and University College London and was presented yesterday, Monday 24th September to a meeting of the British Sleep Society.
Study author, Professor Francesco Cappuccio from the University of Warwick’s Warwick Medical School said the study involved over 10,000 civil servants from the Whitehall II Study and investigated the link between patterns of sleep and mortality rates in the group.
The researchers looked at participants’ sleep patterns during 1985 to 1988 and then again during 1992 to 1993, and monitored their mortality rate until 2004.
They adjusted for a range of factors such as age, sex, marital status, body mass index (BMI), smoking status, physical activity, alcohol consumption, self rated health, blood pressure, cholesterol, illnesses, and others.
This allowed them to see clearly what effect changes in sleep patterns over 5 years had on rates of mortality up to 17 years later.
The results showed that participants who cut their sleeping time from 7 hours (the optimum amount recommended for an adult) to 5 hours or less had a 1.7 increase in mortality risk from all causes, and double the risk of death from cardiovascular causes.
“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,” he added, and also said that:
“Sleep represents the daily process of physiological restitution and recovery, and lack of sleep has far-reaching effects.”
When they looked at too much sleep, Cappuccio and colleagues found a similar effect, it also increased mortality risk.
Those participants who increased sleep duration from 7 to 8 hours a night were more than twice as likely to die, mostly from cardiovascular diseases, as those who did not change their sleep pattern.
Cappuccio said that while short sleep has been shown to be a risk factor for a range of health problems such as weight gain, high blood pressure, and type 2 diabetes, leading to higher risk of death, there has been no similarly detailed investigation into the factors underlying the link between long sleep and increased mortality.
He suggested however that:
“Some candidate causes for this include depression, low socioeconomic status and cancer-related fatigue.”
As far prevention is concerned however, he suggested that:
“Our findings indicate that consistently sleeping around 7 hours per night is optimal for health and a sustained reduction may predispose to ill-health.”
Whitehall II is a prospective, longitudinal study of 10,308 men and women working in the London offices of the British Civil Service when enrolled in 1985.
Data collected at baseline came from clinical exams and self-report questionnaires.
Data has been collected in eight waves since that time, with a ninth due next month, October 2007. Whitehall II is named after an earlier cohort, Whitehall I, that included over 18,000 male civil servants and started in 1967.
“A prospective study of change in sleep duration; associations with mortality in the Whitehall II cohort.”
Jane E. Ferrie, Martin J. Shipley, Francesco P. Cappuccio, Eric Brunner, Michelle A. Miller, Meena Kumari, and Michael G. Marmot.
To be published in SLEEP.
Written by: Catharine Paddock