Although we know that sex has many health benefits — it can lower stress, improve sleep, decrease risk of prostate cancer — scientists can’t always explain why these things are true. A particularly pesky example is the link between increased sexual activity and a decreased risk of heart problems: We’ve known that this connection exists for years, but scientists have only now figured out why.

The answer lies with homocysteine, an amino acid (a protein building block) that’s essential for keeping your body’s cells functioning, but can also cause strokes and heart attacks when too much of it builds up. A group of researchers from Taiwan’s National Defense Medical Center have discovered that having lots of sex is correlated with lower, healthy homocysteine levels.

But here’s the kicker: This connection was only seen in men.

The research, which was published in the Journal of Sexual Medicine in early June, surveyed 2,267 people between the ages of 20 and 59 and compared their sexual activity and homocysteine blood levels for a year. As a whole, the group showed a link between frequent sex and lower homocysteine levels, but when the scientists separated the group by gender and took out control factors, this pattern only revealed itself in the men.

Why the gendered result? The team didn’t specifically study this question, but they do have some ideas. For instance, homocysteine might be especially important to men because they can’t get erections unless they have healthy blood flow; in fact, men with heart problems often experience erectile dysfunction. Women, in contrast, are less dependent on blood flow for arousal. For a man to have penetrative sex, his homocysteine levels need to be low enough so that blood can flow freely to his penis and trigger an erection.

Grey's Anatomy
Apparently the 'Grey's Anatomy' doctors were promoting heart health when they had all that sex.

This is the first study to analyze the relationship between sex and homocysteine levels, which means that the research is groundbreaking but also that it doesn’t tell the full story. The team acknowledges its limits: “The study was a cross-sectional observational investigation,” they explain in the abstract, “and the causal relation should be evaluated in a follow-up study.”

Still, it’s pretty cool that we now have an idea of how sex helps the (male) heart.

How often might a man need to have sex to get this benefit? Well, the lowest amounts of homocysteine were seen in men who had sex at least twice a week. Men who had sex less than once a month had the highest amount of homocysteine in their blood.

“Clinical physicians in primary care should support patients’ sexual activity,” the study concludes. Especially those patients who are at risk of heart disease, which includes men who smoke, have high blood pressure, eat a high-cholesterol diet, or are over 45 years old.

Well, there you go: One more reason to get busy.

Photos via Disney–ABC Domestic Television, That Awkward Moment