Finding the sweet spot of a good night's sleep: Not too long and not too short

Study author Dr Epameinondas Fountas, of the Onassis Cardiac Surgery Centre, Athens, Greece, said: "We spend one-third of our lives sleeping yet we know little about the impact of this biological need on the cardiovascular system."

The study investigated the relationship between sleep duration and cardiovascular disease using a meta-analysis, a statistical tool for combining the results of previous studies on the same topic. The meta-analysis included 11 prospective studies of more than one million adults (1,000,541) without cardiovascular disease published within the last five years.

Two groups, one with short (less than six hours) and another with long (more than eight hours) nightly sleep duration, were compared to the reference group (six to eight hours).

The researchers found that both short and long sleepers had a greater risk of developing or dying from coronary artery disease or stroke. Compared to adults who slept six to eight hours a night, short and long sleepers had 11% and 33% greater risks, respectively, of developing or dying from coronary artery disease or stroke during an average follow-up of 9.3 years.

Dr Fountas 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 inflammation -- all of which have an impact on cardiovascular disease."

A strength of the current analysis is that only prospective studies were included, noted Dr Fountas. This avoids recall bias, a source of systematic error in statistics arising from the inability of participants to accurately recall information.

Dr Fountas concluded: "Having the odd short night or lie-in is unlikely to be detrimental to health, but evidence is accumulating that prolonged nightly sleep deprivation or excessive sleeping should be avoided. The good news is that there are plenty of ways to get into the habit of getting six to eight hours a night -- for example by going to bed and getting up at the same time every day, avoiding alcohol and caffeine before bed, eating healthily, and being physically active. Getting the right amount of sleep is an important part of a healthy lifestyle."