The study found that for men, regular sex was closely linked with higher risk of cardiovascular events, such as heart attacks and strokes.
Researchers said older men could be at risk of over-exertion when attempting to meet the demands of a sexual relationship, creating stress on the heart.
Those who had sex at least once a week had twice the risk of such events, compared to sexually inactive men, the US research found.
For women, no such link was found. Women who reported good sex lives, with high levels of satisfaction, had lower blood pressure – protecting them against heart disease – than those who were sexually inactive.
The study, published in the Journal of Health and Social Behaviour, found older men who found sex with their partner “extremely pleasurable or satisfying” had higher risk of cardiovascular events than men who felt less strongly.
Researchers analysed data from 2204 participants who were aged between 57 and 85 in 2005-2006, with follow-up questions five years later.
Hui Liu, associate professor of sociology at Michigan State University, said the strain and demands from a sexual relationship might take their toll on men as they got older.
“Because older men have more difficulties reaching orgasm for medical or emotional reasons, they may exert themselves to a greater degree of exhaustion and create more stress on their cardiovascular system in order to achieve climax,” Liu said.
Researchers say some of the risks may also have been caused by the use of Viagra and other sexual stimulants.
Benefits were only seen among women who reported high levels of satisfaction and enjoyment from sex.
Researchers said this could reflect the fact that intimacy indicated strong relationships, which might reduce stress. Other factors were the release of the hormone oxytocin, which reduces blood pressure.
Last week a Greek study found that men taking statins experienced a 43% improvement in erections.