But exercise can counteract it. A new study finds 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.