We all know that a healthy diet and lots of exercise will go a long way towards safeguarding our long-term health. But there is another important facet of our lifestyle which medical professionals now believe may be just as important in combating chronic illness, but which gets far less attention -- lack of sleep. And the potential effects of lack of sleep, sleep deprivation, and/or poor sleep quality are striking.
An occasional bad night's sleep makes life difficult the following day. We feel tired, lethargic and irritable, and simply getting through the day feels like a mammoth task. But there is a growing body of evidence which suggests that insufficient or irregular sleep over a long period of time can contribute to chronic illnesses such as heart disease, cancer, obesity and diabetes.
These findings have major implications because most of us are sleeping less than ever before due to the stresses and pressures of modern life. During the last century, the average number of hours spent asleep per night decreased from nine to seven and a half.
"People are getting up earlier and facing in to longer commutes," says Dr Catherine Crowe, a specialist in sleep disorders at the Mater Private Hospital. "They come home late at night and they don't want to go to bed shortly after they come home. All of this results in fewer hours in bed."
In addition, while society generally accepts the benefits of a good diet and exercise, attitudes to the benefits of sleep are more varied. Strangely, being able to survive on a few hours' sleep a night is still considered by many people to be a badge of honour. Margaret Thatcher famously reminded people that she could run a country on four or five hours' sleep. "Those views are very much mistaken," says Prof Walter McNicholas, director of the Sleep Disorders Unit at St Vincent's University Hospital. "People who can survive on a few hours' sleep are very much the exception rather than the rule. The vast majority of us require more sleep than that to function properly and when we do not get it we become chronically tired." While the amount of sleep required to feel refreshed varies from one person to another, most studies concur that the majority of people require between seven and nine hours each night, and that long-term problems can result where you are getting less than seven hours. The Archives of Internal Medicinerecently reported that sleeping less than seven and a half hours per day may be associated with a future risk of heart disease, particularly in people who have night- time hypertension. It is thought that insufficient sleep may trigger stress hormones that bump up the risk of heart attacks and strokes.
The same publication reported in 2003 that women who slept less than five hours a night were 45 per cent more likely to have heart problems than those who slept eight hours. The National Cancer Institute in the US recently reported that lack of sleep can increase the risk of cancer and can even wipe out the health benefits associated with regular exercise. In 1999, a Lancetstudy took 11 healthy men and reduced their nightly sleep to just four hours. After six days they all showed insulin and blood sugar levels which mimicked the body's typical stress response and which were similar to the levels found in people on the verge of diabetes. It is even claimed that chronic sleep loss causes imbalance in the hormones that control appetite and could therefore be a factor in obesity. A 2004 study showed that people who sleep five hours a night are 73 per cent more likely to become obese than those who sleep seven to nine hours. While the evidence for an association between sleep and chronic illness is increasingly compelling, medical science is still grappling with the nature of that association. Is it a cause and effect relationship? And if so, why does sleep disturbance cause these problems? In the case of cancer for example, research suggests that exposure to light at night (due to staying up late or working shifts) reduces the body's level of the hormone melatonin, which is thought to protect against cancer. Researchers believe that this may explain why shift workers show an elevated risk of breast and prostrate cancer compared with the rest of the population.
The lines become blurred, however, if you think about the problem a different way. There are any number of conclusions one can draw from a piece of research which shows that a person who sleeps poorly is more likely to get cardiovascular disease. It could be that the poor sleep causes the cardiovascular disease -- but it could also be that a stressful lifestyle or some other environmental factor causes the poor sleep and the cardiovascular disease. "Sleep is an aspect of our lives that is much under-studied and underappreciated," says Prof McNicholas. "For example, we have research which shows that people who sleep poorly are more likely to have obesity or diabetes. It's like the chicken and egg question -- which came first? "One can theorise about the associations but it is not very well worked out yet." There is less debate, he says, when it comes to the health implications of sleep deprivation caused by underlying disorders like sleep apnoea, the temporary cessation of breathing during sleep. "Sleep apnoea is a major source of sleep disturbance. Up to 10 per cent of adult males and 5 per cent of adult females have it. With sleep apnoea people stop breathing in their sleep dozens or hundreds of times a night. We know that this causes a repetitive sequence of dips in the oxygen levels, which trigger changes in cells and blood vessels. This, in turn, is linked to increased prevalence of cardiovascular disease, blood pressure, heart attacks and strokes."
