London - Rolling over and ignoring the alarm clock in the morning may seem harmless enough.
But those lie-ins could be putting your health at risk.
Sleeping more than eight hours a night significantly increases your chance of a stroke, research suggests.
A study of nearly 290 000 people found seven to eight hours’ sleep a night may protect against the chance of a stroke.
But the US researchers, from the New York University School of Medicine, found that those who sleep for longer than this increase their risk of having a stroke by 146 percent.
And less than seven hours of sleep also increases the risk, by 22 percent.
The academics, who presented their findings at the American Stroke Association Meeting in Los Angeles, analysed factors that contribute to the risk of strokes.
They took into account the health, lifestyle, age and ethnicity of 288 888 adults who took part in a survey from 2004 to 2013.
The researchers also analysed how long people slept and how much exercise they took, such as walking, swimming, cycling or gardening.
Sleeping seven to eight hours a night and taking 30 to 60 minutes of exercise three to six times a week gave the maximum benefits for stroke prevention.
Strokes occur either as a result of a bleed on the brain or when a clot cuts off the blood supply to part of the brain. Each year in England, about 110 000 people suffer a stroke.
It the third most common cause of death, after heart disease and cancer. And brain injuries caused by strokes are a major cause of adult disability.
Smoking, being overweight, not taking much exercise and a poor diet each raise the risk of stroke.
Medical conditions such as high cholesterol, an irregular heartbeat and diabetes also increase risk. There is a growing body of evidence suggesting that between seven and eight hours of sleep is healthiest for most people.
A previous study, published by the Harvard School of Public Health last year, found this amount reduces the chance of a woman suffering type-two diabetes. And a study by Warwick University found those who had less than six hours a night or more than eight had worse memory and decision-making abilities.
Academics have also found that people who have six to eight hours’ sleep a night are likely to live longer and have better health, while those who are getting less than six hours are more at risk of dying prematurely.
Scientists know too little sleep directly disrupts levels of insulin, a hormone that regulates energy through the body’s fat cells.
But they are less sure why too much sleep is problematic. One theory is that sleeping for longer reduces the quality of sleep.
Another is that by sleeping for longer you reduce the time you are active during the day.
Disturbed sleep patterns can impair memory, shrink the brain and raise stress levels.
Anyone whose body clock is regularly disrupted – such as nursing mothers and shift workers – is vulnerable.