Warning! If you don't have regular sex and routinely engage in other types of physical activity, when you decide to get amorous or take a run on the treadmill, it could kill you.

People who engage in physical activity only once in a while--and this includes sexual intercourse--have a far higher risk of suffering a heart attack or sudden cardiac death in the one or two hours after they have exerted themselves, according to a study from the Harvard School of Public Health.

The opposite is also true. The more physical activity you engage in, including having sex, the more protected you are against such a dire demise.

"The triggering effect appeared to be sharpest for people unaccustomed to physical activity," study senior author Jessica K. Paulus, an assistant professor of medicine at Harvard School of Public Health and an adjunct assistant professor of epidemiology at Tufts Medical Center, told HealthDay News. "The recommendation from our paper is consistent with current guidelines, that those looking to initiate an exercise program, especially those at higher risk, do so very gradually and under the care of a clinician or physician."

Paulus and her team conducted a meta-analysis of 14 other studies and determined that people who engaged in "episodic" sexual activity had a 2.7 times higher risk for a heart attack while sporadic physical activity raised the risk 3.5-fold, reports HealthDay News.

While very occasional physical activity also raised the risk of sudden cardiac death fivefold, the overall risk was low because people engaged in these activities so infrequently that the risk went away quickly.

What is the advantage of regular exercise and sex? The study found that each additional time a person exercised in a week, the risk for a heart attack was lowered by 45 percent and for sudden cardiac death by 30 percent.

The takeaway: "The take-home message is that if you have not done much of any physical activity for a long period of time, you should not go out and run a marathon tomorrow but build up more gradually, and that [once you've worked up to it] you should only exercise on the days you brush your teeth, which is hopefully every day," Dr. Robert Ostfeld, associate professor of clinical medicine at Montefiore Medical Center in New York City, told HealthDay News.

The study findings were published in the Journal of the American Medical Association.

--From the Editors at Netscape