We've seen plenty of research on the optimum number of hours' sleep to get for the good of our bodies, but a massive new study of more than 1 million adults has focussed specifically on cardiovascular health.
Based on the new analysis, the researchers put the magic window at between six and eight hours a night in order to protect your heart.
That's probably not a huge surprise, as it's in line with most other sleep recommendations for overall health and wellbeing. But it's more than a lot of us get - more than 40 percent of American adults get less than seven hours' sleep a night.
Interestingly, the study also warned against people getting too much sleep.
The research, which analysed 11 existing studies covering more than 1 million adults, showed that getting less than six hours or more than eight hours was associated with a greater risk of coronary artery disease or a stroke.
That fits in with previous warnings that too much sleep is a reliable indicator of poor health as well as too little sleep – either because it causes health issues to worsen or because it reflects underlying conditions that keep people snoozing for longer.
"Our findings suggest that too much or too little sleep may be bad for the heart," says lead researcher Epameinondas Fountas, from the Onassis Cardiac Surgery Centre in Greece.
"More research is needed to clarify exactly why, but we do know that sleep influences biological processes like glucose metabolism, blood pressure, and inflammation – all of which have an impact on cardiovascular disease."
The meta-analysis crunched the numbers on 1,000,541 people in total, logged in studies published in the last five years. They were split into three groups: less than six hours sleep, between six and eight hours sleep, and more than eight hours sleep.
Based on a follow-up period averaging 9.3 years, the short sleepers were 11 percent more likely, and the long sleepers were 33 percent more likely, to develop or die of coronary artery disease or a stroke.
Coronary artery disease is typically caused by the build-up of cholesterol deposits clogging up the channels responsible for blood flow to and from the heart. Factors such as high blood pressure and a sedentary lifestyle are thought to contribute.
Strokes are linked to heart health and coronary artery disease, and happen when the normal blood flow to the brain is interrupted.
While the study doesn't go into why these correlations might have shown up, the fact that it only analysed prospective studies – where participants are followed over a period of time rather than asked retrospective questions – adds to its usefulness.
And while the researchers are keen to emphasise that the odd lie-in or late night won't do too much damage, over a prolonged amount of time, they might – especially where your heart health is concerned.
As well as hitting the sweet spot of between six and eight hours, the team behind the study recommends avoiding alcohol and caffeine before bed, making regular exercise a part of your routine, and watching what you eat.
Doctors should also be watching out for patients who are spending too long or not long enough in bed. The details of how this fits with the biology of the heart aren't yet clear, but it seems clear there's a definite link here – which future research can shed more light on.
As we know from other studies, going without sleep can cause significant damage to the brain as well, even if we're not yet sure how or why this occurs. Getting enough shut-eye is a crucial part of keeping our bodies running well.
"We spend one-third of our lives sleeping yet we know little about the impact of this biological need on the cardiovascular system," says Fountas.
The research has yet to be peer-reviewed and published, but has been presented at the European Society of Cardiology Congress 2018.