Aim for six to seven hours of sleep a night to maximise health health, a study has suggested.
The optimal amount of shut-eye has long been debated, with some people able to get by on less sleep than others.
The NHS recommends adults aim for six to nine hours of sleep a night, however, medics from Henry Ford Hospital in Detroit have suggested six to seven hours may be the sweet spot when it comes to heart health.
Although more research is needed, it seems too much or too little sleep may trigger inflammation that damages the heart.
Unlike a person's age or genetics, sleep is somewhat controllable, allowing people to actively reduce their heart disease risk, according to the medics.
"Sleep is often overlooked as something that may play a role in cardiovascular disease and it may be among the most cost-effective ways to lower cardiovascular risk," said lead author Dr Kartik Gupta.
"Based on our data, sleeping six to seven hours a night is associated with more favourable heart health."
Heart disease is behind more than one in four deaths in the UK alone.
Not smoking, eating well and exercising regularly are known to ward off cardiovascular complications, however, the role of sleep was less clear.
To learn more, the Detroit medics analysed over 14,000 participants – average age 46 – of the National Health and Nutrition Examination Survey.
Less than 10% of the participants had experienced heart disease before the study.
The participants were divided into groups based on the amount of sleep they claimed to average each night.
The medics also assessed the participants' so-called atherosclerotic cardiovascular disease (ASCVD) risk score.
This calculates how likely someone is to have a heart attack or stroke, or die from hardening of the arteries, over the next 10 years. It takes into account the individual's age, sex, ethnicity, blood pressure and cholesterol.
A score of less than 5% is considered low risk.
Overall, the participants' ASCVD score averaged at 3.5%, as presented at the American College of Cardiology's 70th annual scientific session.
Nevertheless, there was a U-shaped relationship between a patient's score and their sleep duration, with six to seven hours being the lowest risk.
Over the next 10 years, the participants' estimated ASCVD score was 3.3% among those who had six to seven, or more than seven, hours sleep a night.
This is compared to a score of 4.6% among those who slept for under six hours.
The participants were also followed for around 7.5 years, to uncover who died of a heart attack, stroke or heart failure; when the organ cannot pump blood around the body efficiently.
"Participants who slept less than six hours or more than seven hours had a higher chance of death due to cardiac causes," said Dr Gupta.
"ASCVD risk score was, however, the same in those who sleep six to seven hours versus more than seven hours."
The score may not have captured an elevated heart disease risk in the subgroup who slept for more than seven hours, with the risk perhaps stronger in those who got by on less than six hours, according to the medics.
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At the start of the study, the medics also measured the participants' C-reactive protein (CRP) levels, a marker of inflammation associated with heart disease.
"Participants who sleep less or more than six to seven hours have higher ASCVD risk scores, which is likely driven by heightened inflammation as measured by CRP, which was found to be higher among those who had less or more sleep," said Dr Gupta.
"The effect of sleep probably accrues over time. It takes time for the damage to happen."
The team wants patients to be asked routinely about their sleep during medical appointments.
"It's important to talk about not only the amount of sleep but the depth and quality of sleep too," said Dr Gupta.
"Just because you are lying in bed for seven hours doesn't mean you are getting good quality sleep."
The study did not assess how well or deeply the participants slept. For example, sleep apnoea – when a patient wakes in the night due to their breathing stopping and starting – is increasingly being linked to heart disease.
Tips for a good night's sleep
People who struggle to sleep are advised to go to bed and wake up at the same time every day, even on weekends.
Winding down with gentle yoga, a warm bath, soothing music or a relaxing book can also help. Writing a to-do list for the next day may also calm a frazzled mind.
Experts also recommend people avoid screens, like their phone, for around an hour before bed.
Bedrooms should also be "sleep friendly", with a comfortable mattress, pleasant temperature and black-out curtains, if necessary.
Keeping a sleep diary can help people link a poor night's shut eye to lifestyle habits, like drinking too much coffee or alcohol.
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