More or less could increase the risk of coronary artery disease or a stroke, according to the findings of a new study.
The research, presented at the European Society of Cardiology Congress in Munich, Germany, suggests sleep deprivation and excessive hours in bed should be avoided for optimum heart health.
Study author Dr Epameinondas Fountas, of the Onassis Cardiac Surgery Centre in Athens, Greece, said: "Our findings suggest that too much or too little sleep may be bad for the heart.
"More research is needed to clarify exactly why, but we do know that sleep influences biological processes like glucose metabolism, blood pressure, and inflammations - all of which have an impact on cardiovascular disease."
Data from more than one million adults from 11 studies was analysed as part of the research.
Those who slept for less than six hours per night or more than eight hours were at an increased risk of developing or dying from coronary artery disease or a stroke, according to the study.
Compared to adults who got six to eight hours of shut-eye a night, "short sleepers" had an 11 per cent greater risk while "long sleepers" had 33 per cent increased risk over the next nine years, the researchers said.
