Ivory Towers: One less thing to worry about: sex, heart attacks and Swedish optimism.

Is sex dangerous? Two research papers published this month throw a litle bedside light on the subject. At Harvard Medical School they were interested in whether sexual activity can bring on a heart attack. They reported their results in "Triggering Myocardial Infarction by Sexual Activity," in the Journal of the American Medical Association (8 May 1996).

"Anecdotal case reports suggest that sexual activity can trigger myocardial infarction (MI)," the paper begins, "but the relative risk of MI after sexual activity, the frequency of sexually-triggered MIs, and possible methods of reducing risk have not been studied. The lack of data...causes a major problem for patients who have cardiac disease, their spouses, and the health care professionals."

The researchers surveyed 1,663 survivors of acute heart attacks "who were willing to disclose information regarding their sexual activity". Of those 1,663, only 858 had been sexually active in the year preceding the MI, and only 27 reported sexual activity in the two hours prior to the MI. While the figures did show an increased tendency to have a heart attack in the two hours following sexual activity, the risk was no greater for subjects with a previous history of heart trouble than for those without prior cardiac disease. "Sexual activity appeared to trigger MI in only about 0.9 per cent of cases."

Furthermore: "regular exercise can reduce and possibly eliminate, the small and transient increased risk of MI associated with sexual activity." Indeed, of the 27 subjects who suffered heart attacks within two hours of sex, 23 were among the group of "most sedentary" individuals. For those who took regular exercise, the risk of post-coital heart attack was no greater than normal.

As the editorial in the JAMA says, the research gives us "one less thing to worry about". The risk that a 50-year-old, nonsmoking, non-diabetic man will experience an MI is approximately one per cent per year, which is about one in a million per hour. "By engaging in sexual activity such an individual would only increase his hourly risk to two in a million, and only for a two-hour period."

The bad news, however, is that a Swedish study published last Friday showed that men with a highly active sex life run a greater risk of contracting prostate cancer. "We don't think it's the sexual activity in itself," said the doctor who conducted the study, "it might be some sort of hormonal factor that also affects sexual drive." So the conclusion is clear: go ahead and enjoy yourselves. You probably won't have a heart attack, and if you get cancer of the prostate, well, you would probably have had it anyway.

WILLIAM HARTSTON