Men who sleep less than six hours a night may be at an increased risk of cardiovascular disease compared to those who sleep between seven and eight hours a new study suggests. The study showed that poor quality sleep of less than six hours increases the risk of atherosclerosis by 27 per cent compared to seven to eight hours of sleep. Atherosclerosis refers to the build-up of fats cholesterol and other substances in and on the artery walls throughout the body. On the other hand women who slept more than eight hours a night had an increased risk of atherosclerosis.