Sitting too much during the day has been linked to a host of diseases, from obesity to heart problems and diabetes, as well as early death. It's not hard to understand why: being inactive can contribute to weight gain, which in turn is a risk factor for heart attack, stroke, hypertension and unhealthy blood sugar levels. On top of everything else, sitting has detrimental effects on cells at the biological level, according to a new report published in the American Journal of Epidemiology. From a report on Time: In the new study, scientists led by Aladdin Shadyab, a post-doctoral fellow in family medicine and public health at the University of California San Diego, traced sitting's impact on the chromosomes. They took blood samples from nearly 1,500 older women enrolled in the Women's Health Initiative, a long-term study of chronic diseases in post-menopausal women, and focused on the telomeres: the tips of the tightly packed DNA in every cell. Previous studies have found that as cells divide and age, they lose bits of the telomeres, so the length of this region can be a marker for how old a cell (and indirectly the person the cells belong to) is. The researchers compared telomere length to how much the women exercised, to see if physical activity affected aging.