Nov 6, 2005
Sleep on it

Having little or erratic sleep can increase your risk of cancer and obesity

WITH a good night's rest increasingly losing out to the Internet, late-night cable and other distractions of modern life, growing scientific evidence suggests that too little or erratic sleep may be taking a toll on your health.

Failing to get enough sleep or sleeping at odd hours heightens the risk of a variety of major illnesses, including cancer, heart disease, diabetes and obesity.

A big new study of Americans, for example, suggests that the nation's obesity epidemic is being driven, at least in part, by a corresponding decrease in the average number of hours that they are sleeping, possibly by disrupting hormones that regulate appetite.

The analysis of nearly 10,000 adults found that those between the ages of 32 and 49 who sleep less than seven hours a night are significantly more likely to be obese.p> The study follows a series of others that have found similar associations with other illnesses, including several reports from the Harvard-run Nurses' Health Study that have linked insufficient or irregular sleep to increased risk of colon cancer, breast cancer, heart disease and diabetes.

The amount of necessary sleep varies from person to person, experts say. But most people apparently need between seven and nine hours, with studies showing that an increased risk of disease starts to kick in when people get less than six or seven.

'The strongest evidence right now is of the risk of overall mortality,' said Mr Sanjay Patel of Harvard Medical School. He led a study involving more than 82,000 nurses that found an increased risk of death among those who had less than six hours' sleep a night.

Physiologic studies suggest that a sleep deficit may put the body into a state of high alert, increasing the production of stress hormones and driving up blood pressure, a major risk factor for heart attacks and strokes.

Moreover, people who are sleep- deprived have elevated levels of substances in the blood that indicate a heightened state of inflammation in the body, which has also recently emerged as a major risk factor for heart disease, stroke, cancer and diabetes.

After several studies found that people who work at night appear unusually prone to breast and colon cancer, researchers investigating the possible explanation for this association found exposure to light at night reduces levels of the hormone melatonin.

Melatonin is believed to protect against cancer by affecting levels of other hormones, such as oestrogen.

'Melatonin can prevent tumour cells from growing - it's cancer-protective,' said Ms Eva Schernhammer of Harvard Medical School, who has conducted a series of studies on volunteers in sleep laboratories. 'The theory is, if you are exposed to light at night, on average you will produce less melatonin, increasing your cancer risk.'

Other researchers are exploring a possible link to other malignancies, including prostate cancer.

'There's no reason it should be limited to breast cancer, and it wouldn't necessarily be restricted to people who work night shifts. People with disrupted sleep or who are up late or get up frequently at night could potentially have the same sort of effect,' said Mr Scott Davis of the University of Washington.

'The research in this area is in its infancy,' said Ms Eve Van Cauter of the University of Chicago. 'This is the tip of the iceberg that has just begun to emerge.' -- LAT-WP

from The Sunday Times