Correlating Time Spent Sedentary with Cardiovascular Disease Risk
Epidemiological data on human health doesn't lend itself to concrete interpretation. For example, the role of time spent sitting or otherwise sedentary in the development of cardiovascular disease remains debated. Some studies suggest that sedentary time contributes to risk independently of level of exercise, others suggest that recommended levels of exercise eliminate any relationship between sedentary time and risk of disease. There remain the questions of the degree to which sedentary behavior is a proxy for other contributions to long-term health such as diet and weight. This is before we even arrive at the question of biological mechanisms and their relative importance.
Insufficient exercise is a known risk factor for cardiovascular disease (CVD). Over 150 minutes of moderate-to-vigorous physical activity per week is recommended by current guidelines to promote heart health. However, study experts say exercise is only a small fraction of overall daily activity, and the current guidelines don't provide specific guidance on sedentary behavior which accounts for a much larger portion of daily activity, despite evidence that it's directly linked with CVD risk. This study examined the amount of sedentary time at which CVD risk is greatest and explored how sedentary behavior and physical activity together impact the chances of atrial fibrillation (AF), heart failure (HF), myocardial infarction (MI), and cardiovascular mortality.
Among the 89,530 study participants of the UK Biobank, the average age was 62 years and 56.4% were women. Participants submitted data from a wrist-worn triaxial accelerometer that captured movement over seven days. The average sedentary time per day was 9.4 hours. After an average follow-up of eight years, 3,638 individuals (4.9%) developed incident AF, 1,854 (2.1%) developed incident HF, 1,610 (1.84%) developed indecent MI, and 846 (0.94%) died of cardiovascular causes, respectively.
The effects of sedentary time varied by outcome. For AF and MI, the risk increased steadily over time without major shifts. For HF and CV mortality, increase in risk was minimal until sedentary time exceeded about 10.6 hours a day, at which point risk rose significantly, showing a "threshold" effect for the behavior. For study participants who met the recommended 150 minutes of moderate-to-vigorous physical activity or more, the effects of sedentary behavior on AF and MI risks were substantially reduced, but effects on higher risk of HF and cardiovascular mortality remained prominent.