Why We Sleep: Unlocking the Power of Sleep and Dreams

by Matthew Walker

Take the results of a 2011 study that tracked 474,684 men and women of varied ages, races, and ethnicities across eight different countries. Short sleep was associated with more than a 45 percent greater risk of fatal and nonfatal coronary heart disease within seven to twenty-five years from the start of the study. A similar relationship was observed in a Japanese study of 2,282 male workers. Over a fourteen-year period, sleeping less than six hours a night was associated with more than a three times greater risk of suffering a cardiovascular or coronary event, such as sudden cardiac death. This was relative to those sleeping 7 to 7.9 hours a night. I should note that in many of these studies, the relationship between short sleep and heart failure remains strong even after controlling for other known cardiac risk factors, such as smoking, physical activity, and body mass. A lack of sleep more than accomplishes its own, independent attack on the heart.