Middle-aged men who sleep less than five hours a night have twice the risk of developing a major cardiovascular event such as heart attack or stroke, a study has found.

Previous studies have generated conflicting evidence on whether short sleep is associated with a greater chance of having a future cardiovascular event. The study investigated this relationship in 50-year-old men.

"For people with busy lives, sleeping may feel like a waste of time but our study suggests that short sleep could be linked with future cardiovascular disease," said Moa Bengtsson, of the University of Gothenburg in Sweden.

In 1993, 50 per cent of all men born in 1943 and living in Gothenburg were randomly selected to participate in the study.

Of the 1,463 invited, 798 (55 per cent) men agreed to take part. Participants underwent a physical examination and completed a questionnaire on current health conditions, average sleep duration, physical activity, and smoking.

The men were divided into four groups according to their self-estimated average sleep duration at the start of the study: five or less hours, six hours, seven to eight hours, and more than eight hours.

Participants were followed-up for 21 years for the occurrence of major cardiovascular events, which included heart attack, stroke, hospitalisation due to heart failure, coronary revascularization, or death from cardiovascular disease.

High blood pressure, diabetes, obesity, current smoking, low physical activity, and poor sleep quality were more common in men who slept five or fewer hours per night compared to those who got seven to eight hours.

Compared to those with normal sleep duration, men who slept five or fewer hours per night had a two-fold higher risk of having a major cardiovascular event by age 71.

The risk remained doubled after adjusting for cardiovascular risk factors at the start of the study including obesity, diabetes, and smoking.

"Men with the shortest sleep duration at the age of 50 were twice as likely to have had a cardiovascular event by age 71 than those who slept a normal amount, even when other risk factors were taken into account," said Bengtsson.

"In our study, the magnitude of increased cardiovascular risk associated with insufficient sleep is similar to that of smoking or having diabetes at age 50," she said.

"This was an observational study so based on our findings we cannot conclude that short sleep causes cardiovascular disease, or say definitively that sleeping more will reduce risk," she added.

"However, the findings do suggest that sleep is important -- and that should be a wake-up call to all of us," Bengtsson said.