Over the past 20 years, dozens of epidemiological studies have shown that people who are physically active and who exercise regularly have a decreased risk of heart disease, whether they have risk factors for heart disease or not. As a consequence of our modern lifestyle, our time spending sedentary activities has skyrocketed to a point where few of us reach a minimum of 10,000 steps per day. While some of us try to compensate by performing team sports, going out for a jog or spending an hour at the gym 2-3 time a week, the impact of too much sitting (or too much sedentary time) on heart disease risk is not well established.

At the last scientific meeting of the American College of Cardiology, investigators of the Dallas Heart Study presented results that shed light on the association between sedentary activities and the risk of vascular calcifications (http://www.abstractsonline.com/pp8/#!/3658/presentation/35957). The researchers measured sitting/sedentary time using accelerometer data from wristwatches (4 days minimum) and assessed the presence of vascular calcifications using computed tomography in more than 2,000 participants aged 20-76. More than half of the study participants were women and half were black. The authors confirmed that the amount of time spent performing moderate-to-vigorous physical activity was inversely associated with the presence of vascular calcifications. However, after adjusting for traditional risk factors for heart disease, this association was no longer observed, which suggest that the association between physical activity and vascular calcification could be explained by the fact that people who are physically active are younger, have a lower body weight, lower cholesterol, etc. On the other hand, the authors found that each hour of sedentary time increased the risk of having vascular calcifications by 10%, irrespectively of the presence/absence of cardiovascular risk factors. Interestingly, the association between sitting time and vascular calcifications was completely independent of the physical activity level of study participants.

Based on the results of this study, one might suggest that lack of exercise and too much sitting could be considered as two distinct risk factors for heart disease, sitting operating via vascular calcifications and exercise via other mechanisms. However, experimental studies will be required to confirm this hypothesis. Additionally, results of this study should have important public health implications as they suggest that targeting sedentary behaviours could be just as important as recommending people to exercise more. While physical activity levels have reached an all-time low in Western societies, recommending that people get at least 150 minutes of moderate-to-vigorous physical activity per week is more important than ever. However, although additional studies with longitudinal results are needed to confirm the results of the Dallas Heart Study, getting children and adults to decrease sitting time on top of recommending them to perform enough physical activity may eventually become our next goal in the fight against chronic societal diseases such as heart disease.