Most research into sleep has concentrated on how the quality and the quantity we get affects our health and well-being.
Now a new study suggests that the time we go to be bed may also be an important factor in protecting us from illnesses, especially heart attacks and strokes, both of which become higher risk as we get older.
It seems that between 10 and 11 at night is the ideal time to go to bed because that best suits the body’s internal 24-clock system, known as the circadian rhythm.
The findings come from a study by researchers with the Biobank project in the UK.
Biobank collates data from hundreds of thousands of people who agree to take part in tests and share their medical conditions to help improve health care in the future.
The researchers collected data from 88,026 Biobank volunteers, over a seven-day period using a wristwatch-like device to monitor their sleep patterns. Their average age was 61
The participants also filled in questionnaires on their lifestyles and underwent physical assessments.
Over the following six years the researchers monitored the heart and circulatory health of the volunteers.
They found that 3,172 of the adults developed cardiovascular disease. The highest rate was found in those who went to sleep at midnight or later, and lowest in those who went to sleep between 10 and 11pm.
Those who went to bed between 11pm and 11.59pm had a 12 per cent higher risk of cardiovascular disease than people going to sleep between 10pm and 10.59pm.
The risk was 25 per cent higher for those who went to bed after midnight and 24 per cent for those who retired before 10pm. So going to be before 10 is only marginally better than going after midnight.
The figures took into account adjustments for sleep duration and sleep irregularity.
The researchers also accounted for other factors that can affect heart risk, such as age, weight and cholesterol levels and the connection remained.
The author of the study, Dr David Plans, from Exeter University, 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.
“The riskiest time was after midnight, potentially because it may reduce the likelihood of seeing morning light, which resets the body clock.”
“The body has a 24-hour internal clock — circadian rhythm — that helps regulate physical and mental functioning. The results suggest that early or late bedtimes may be more likely to disrupt the body clock, with adverse consequences for cardiovascular health.”
Regina Giblin, senior cardiac nurse at the British Heart Foundation, said: “This large study suggests that going to sleep between 10 and 11pm could be the sweet spot for most people to keep their heart healthy long-term.
“However, it’s important to remember that this study can only show an association and can’t prove cause and effect. More research is needed into sleep timing and duration as a risk factor for heart and circulatory diseases.
“But sleep isn’t the only factor that can impact heart health. It’s also important to look at your lifestyle as knowing your numbers such as blood pressure and cholesterol levels, maintaining a healthy weight and exercising regularly, cutting down on salt and alcohol intake, and eating a balanced diet can also help to keep your heart healthy.”
The study is titled Accelerometer-derived sleep onset timing and cardiovascular disease incidence: a UK Biobank cohort study and is published in full in the European Heart Journal