The study found that compared to sleep onset from 10pm to 10.59pm, there was a 25 per cent higher risk of cardiovascular disease brought on by dropping off at midnight or later.

There was a 12 per cent greater risk caused by falling asleep from 11pm to 11.59pm, and a 24 per cent increased risk if you doze off before 10pm, according to the study.

Further analysis by sex suggested the association with increased cardiovascular risk was stronger in women, with only sleep onset before 10pm remaining significant for men.

"The body has a 24-hour internal clock, called circadian rhythm, that helps regulate physical and mental functioning," study author Dr David Plans, of the University of Exeter in the UK, said.

"While we cannot conclude causation from our study, the results suggest that early or late bedtimes may be more likely to disrupt the body clock, with adverse consequences for cardiovascular health."

While a number of studies have investigated the link between sleep duration and cardiovascular disease, the relationship between sleep timing and heart problems has not received as much attention.

The study included 88,026 people in the UK recruited between 2006 and 2010.

The average age was 61 years, with a range between 43 and 79, and 58 per cent were women.

Researchers collected data on sleep onset and waking time over seven days using a device worn on the wrist.

Participants completed demographic, lifestyle, health and physical assessments and questionnaires.

They were then followed up for a new diagnosis of cardiovascular disease, which was defined as a heart attack, heart failure, chronic ischaemic heart disease, stroke, and transient ischaemic attack.

During an average follow-up of 5.7 years, 3172 participants (3.6 per cent) developed cardiovascular disease, according to the study published in European Heart Journal - Digital Health, a journal of the European Society of Cardiology.

According to the paper, the incidence was highest in those with sleep times at midnight or later and lowest in those with sleep onset from 10pm to 10.59pm.

"Our study indicates that the optimum time to go to sleep is at a specific point in the body's 24-hour cycle and deviations may be detrimental to health," Dr Plans said.

"The riskiest time was after midnight, potentially because it may reduce the likelihood of seeing morning light, which resets the body clock."

"While the findings do not show causality, sleep timing has emerged as a potential cardiac risk factor - independent of other risk factors and sleep characteristics."

Australian Associated Press