A recent study by specialists in Norway and Taiwan involving almost 400,000 individuals suggested that less than four hours of sleep per night increased the risk of heart disease by 36% and more than eight hours of sleep a night raises the same risk by 28%.
Analyses were adjusted for other risk factors, such as smoking, alcohol use and obesity. The study, led by researcher at the Norwegian University of Science and Technology Linn Beate Strand and published in the International Journal of Cardiology, has not identified any increased risk of heart disease with sleeping between four and six hours a night, or between six and eight hours. Researchers asked 392,164 adults between 1998 and 2011 of both sexes who underwent coronary exams how many hours they slept at night.
The results were obtained through the analysis of 711 patients who died of heart disease during the 13 years of the follow-up period. Previous studies have suggested that the lack of sleep increases blood pressure and the epinephrine secretion, which are risk factors for heart disease. The novelty of this study, which involves a significant sample, lies in that people who sleep more than eight hours a night also face a high risk of heart disease. Medical causes of this phenomenon are yet to be explained, however.