The chance of death of those who napped among 16,000 people increased by around 32 per cent
Adults who sleep for an hour or more in the day increased the chances of premature death by almost a third, scientists found.
The biggest risks appear to be associated with lung diseases, such as bronchitis, emphysema and pneumonia.
Adults who nap every day are up to two-and-a-half times more likely to die from respiratory illnesses than those who don’t.
Researchers said that this could be because napping triggers inflammation in the body.
However, the findings, published in the American Journal of Epidemiology, also suggested that dozing during the day could be a signal that the person already has lung disease.
Experts at Cambridge tracked more than 16,000 British men and women over 13 years.
They studied adults who, in the late nineties, signed up to a major research project investigating the effects of diet and lifestyle on cancer.
As part of the project, volunteers gave details of their sleeping habits – including whether they took a nap in the day.
Hollowed them up for 13 years and recorded the number of deaths – just over 3,000 – and what caused them.
When they matched mortality rates with sleeping habits, they found the risk of death increased slightly by about 14 per cent in people who dozed less than an hour in the day.
READ The Tales About A Snake, An Accident And Missing Millions
But if their naps lasted more than an hour, the risks increased by 32 per cent.
When they looked at causes of death, they found the chances of dying from a respiratory illness more than doubled if naps lasted over an hour.
But the report added: “It remains plausible that napping might be an early sign of system disregulation and a marker of future health problems.”
Professor Jim Horne, from the Sleep Research Centre at Loughborough University, said short naps can still be a major help.
He said: “The findings actually show that the great majority – about 85 per cent – of those people who napped less than one hour were at no greater risk.”
He said it is possible that people in the study with serious and incurable lung illnesses might even have benefited from snoozing in the day and that napping ‘may not have hastened death but delayed it’.
Last year, a study in China – where taking a post-lunch snooze is very popular – found napping for more than 30 minutes at a time raised the chances of developing type two diabetes.
But scientists could not be sure that it wasn’t hidden diabetes that made people sleep, rather than napping triggering the disease.
However, other studies have suggested a quick doze may slash the risk of heart attacks and strokes by more than a third.