But the study by Tufts Medical Center researchers just out in the Journal of the American Medical Association is by no means a justification for refraining from exercise. On the contrary: It also found that regular exercise significantly reduces those heart risks, so exercising today could mean lower risk if you exercise — or attempt certain other potentially strenuous activities — tomorrow.
Researchers analyzed 14 studies looking at the effects of exercise and sex on sudden cardiac death and myocardial infarction, or heart attack. They found periodic physical activity was associated with a 3.5-times increased risk of heart attack, and occasional sexual activity was linked with a 2.7-times increased risk of heart attack. Periodic physical activity was also linked with an increased risk of sudden cardiac death.
However, the more exercise people did, the lower their risk of acute cardiac events. For each time someone exercised during the week, the relative risk of a bout of exercise prompting a heart attack decreased by about 45%, and for sudden cardiac death it decreased 30%.