One interesting correlation that has emerged fairly recently from very large epidemiological studies of health is that sitting time is associated with worse health and a shorter life expectancy independently of exercise. Explaining why this is the case is a still a fairly speculative process at this stage, but a first step is to try to pin down specific aspects of age-related disease and degeneration and associate those with sitting time.
Here researchers focus on the calcification of blood vessels, a part of the mineralization of connective tissues that occurs in aging. Along with cross-linking due to sugary metabolic waste, this process stiffens blood vessel walls. This in turn causes hypertension, contributes to atherosclerosis, and causes all sorts of further damage to tissues throughout the body due to structural failure in small blood vessels and inappropriate blood pressure. As for cross-links, there is a minimal amount of research taking place on how to demineralize tissues, but far from enough.
Sitting for many hours per day is associated with increased coronary artery calcification, a marker of subclinical heart disease that can increase the risk of a heart attack. The study found no association between coronary artery calcification and the amount of exercise a person gets, suggesting that too much sitting might have a greater impact than exercise on this particular measure of heart health. The results suggest that exercise may not entirely counteract the negative effects of a mostly sedentary lifestyle on coronary artery calcium. "It's clear that exercise is important to reduce your cardiovascular risk and improve your fitness level. But this study suggests that reducing how much you sit every day may represent a more novel, companion strategy (in addition to exercise) to help reduce your cardiovascular risk."
Coronary artery calcification, measured through a non-invasive CT heart scan, indicates the amount of calcium contained in plaques within the heart's arteries. Coronary artery disease occurs when such plaques accumulate over time, causing the arteries to narrow. Analyzing heart scans and physical activity records of more than 2,000 adults living in Dallas, the researchers found each hour of sedentary time per day on average was associated with a 14 percent increase in coronary artery calcification burden. The association was independent of exercise activity and other traditional heart disease risk factors. A particular strength of the study is that the researchers used a motion-tracking device called an accelerometer to measure how long participants were sedentary and how much they exercised, whereas most previous studies have relied on surveys.