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Sleep less and you're more likely to die

Sleep less and you're more likely to die
If you notice that you're getting less and less sleep each night, it's time to take measures and make sure that you get 7-8 hours' sleep per night. If you don't, you may be doubling your risk of having a heart attack, epidemiologists at University College London discovered.

Health scientists have started to realise over the last five years that sleep is as important as nutrition and exercise. And they haven't just made this up; their reasoning is based on a growing pile of studies. The better you sleep, the more resistance you have to viruses, the more testosterone you body produces, the more muscle mass your body builds up, the less likely you are to put on weight, the more oxygen your body is capable of absorbing and on top of all that you're more attractive too.

Oh yes. And you live longer too, if you sleep well.

If sleep is so healthy, then you'd expect that a change in sleep behaviour would also affect your risk of mortality, the authors of the study reasoned. Because you only know for certain if you can demonstrate it scientifically, the researchers followed a group of ten thousand British civil servants for almost thirty years. Most of them did sedentary work, and people who lead a sedentary lifestyle need less sleep than people who do physical work or athletes.

In the period 1985-1988 the researchers measured the amount of sleep the civil servants got each night [Phase 1], and in 1992-1993 they did the same again [Phase 3]. The researchers followed the participants until 2004, which enabled them to compile the table shown below. Click on it and a bigger figure will appear.

When the researchers looked at whether there was a relationship between the length of sleep of the subjects and their mortality, they found this was indeed the case, on both occasions. Seven hours' sleep a night was optimal, they said. Among the civil servants who slept for five hours or less, and those who slept for nine hours or more, they observed a noticeable rise in mortality.

The extent to which sleep leads to an increase in mortality is not known. It may only be an apparent relationship. People recovering from cancer sleep more, as do depressed or unemployed people. Unemployment, depression and cancer all raise mortality.

Sleep less and you're more likely to die

The British researchers then looked at changes in the amount of sleep and produced a table of which part is reproduced below. Click here for the complete version.

Sleep less and you're more likely to die

For the participants who initially slept 5-6 hours a night and then started to sleep more the researchers noticed that their mortality declined. For the participants who slept 6-8 hours a night and then started to sleep less, their mortality increased by sixty percent. Their chance of a fatal heart attack actually doubled.

For the civil servants who already slept enough and then started to sleep more, their mortality also rose. In this case the chance of dying from factors other than cardiovascular disease rose. Just how more sleep can be unhealthy the researchers are not sure, but they have a few theories.

"It is possible that older and nonworking participants spend more time in bed and reported this rather than time asleep", they write. "An examination of the correlates of long sleep in the Nurses Health II study demonstrated strong associations with depression and low socioeconomic status, in particular unemployment. Another possible candidate is cancer-related fatigue. However, it will remain difficult to propose underlying mechanisms to explain our observed association between an increase in sleep and non-cardiovascular mortality until the study has sufficient power to examine the constituent causes of death that make up the non-cardiovascular category."

"Our findings suggest that either a decrease in sleep duration from a regular 6, 7, or 8 hours or an increase from a regular 7 or 8 hours predict all-cause mortality", the researchers conclude. "A decrease in sleep duration affects all-cause mortality via increases in cardiovascular deaths, while an increase in sleep duration affects overall mortality via an increase in non-cardiovascular deaths."

Sleep. 2007 Dec;30(12):1659-66.

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