For a long time now I have seen decent sleep habits as one of the pillars of good health and optimal wellbeing. Just recently two studies were published which highlighted the potential importance of sleep again. One of these was published on Christmas eve in the Journal of American Medical Association [1]. This study found that in a group of individuals followed over five years, longer sleep time was associated with a reduced risk of calcification (calcium deposition) in the arteries around the heart (coronary arteries). Calcification of the coronary arteries is used as a measure of the extent of ‘atherosclerotic plaque’ (the substance that causes narrowing in arteries in heart disease). The results of this study showed that for each additional hour individuals slept for each night, risk of coronary artery calcification fell by about a third.
The link between sleep duration and coronary artery calcification may be interesting to some, but it’s not necessarily as meaningful as looking at the relationship between sleep and say, actual heart disease or, even better, death due to heart disease. On December 15 a study was published in the American Journal of Epidemiology which assessed the relationship between sleep duration and risk of death from heart disease [2]. Compared to individuals sleeping 7 hours a night, those sleeping 5 hours or less or 9 hours or more were at a 57 and 79 per cent increased risk of dying from heart disease.
There is other evidence that links short and long sleep duration with enhanced risk of cardiovascular disease. Some of the potential mechanisms that might be behind the association between shorted sleep times and cardiovascular disease were explored in this recent blog post. The relationship between longer sleep duration and enhanced cardiovascular disease risk might theoretically be due to the fact that sick people tend to sleep longer (i.e. it’s the sickness causing the long sleep time, not the other way round). In the American Journal of Epidemiology study the authors attempted to account for this in their analysis (partly by excluding people who were known to be suffering from hypertension and/or diabetes at the start of the study). However, having done this, the results were the same. The suggestion here being that longer sleep times might actually increase heart disease risk.
I do believe that, as with most things, our need for sleep is a somewhat individual affair. However, there does seem to be good reason to, as a general, attempt to get a good 7-8 hours a night.
References:
1. Ryan King C, et al. Short Sleep Duration and Incident Coronary Artery Calcification
JAMA. 2008;300(24):2859-2866
2. Shankar A, et al. Sleep Duration and Coronary Heart Disease Mortality Among Chinese Adults in Singapore: A Population-based Cohort Study. American Journal of Epidemiology 2008 168(12):1367-1373
