Testosterone is often treated as a marker of health and vigor, especially in men. But new genetic evidence suggests it’s not all good: higher lifelong levels of the hormone may also increase the risk of heart disease.

Researchers at the University of Cambridge analyzed data from over 1.4 million people. They found that men with gene variants linked to higher circulating testosterone had a 17% greater risk of developing coronary artery disease. In practical terms, that could raise a man’s lifetime risk from about 7.3% to 8.5%. The results were published in The Journal of Clinical Endocrinology and Metabolism.

Observational studies have often linked low testosterone to heart disease. Those studies are a bit misleading, the authors of the new analysis argue argue, because illnesses like obesity and type 2 diabetes both lower testosterone and raise heart risk, masking the results. Genetics offers a way around that problem.

To untangle cause from coincidence, the Cambridge team used a method called Mendelian randomization. It relies on naturally occurring genetic differences that influence hormone levels from birth. Because these variants are randomly assigned, they act like a lifelong clinical trial. It’s like a natural experiment.

The researchers analyzed genetic data from more than 400,000 participants in the UK Biobank, alongside coronary artery disease data from over a million people in the CARDIoGRAMplusC4D consortium. They looked for gene variants that reliably raise testosterone and then asked whether carriers of those variants were more likely to develop blocked coronary arteries.

In men, they were.

The increased risk appeared to be partly driven by blood pressure. Men with genetically higher testosterone also tended to have higher systolic and diastolic blood pressure, a well-known contributor to heart disease. When the researchers adjusted for blood pressure, the testosterone effect weakened, suggesting blood pressure may explain part—but not all—of the association.

In women, by contrast, the study found no clear link between genetically higher testosterone and coronary artery disease.

That sex difference matters. Testosterone’s biology and its genetic regulation differs sharply between men and women. Lumping the sexes together, the authors argue, has obscured important risks in earlier research.

The findings arrive at a moment when testosterone use is expanding well beyond its original medical niche. Testosterone replacement therapy is an approved treatment for hypogonadism, a condition marked by fatigue and sexual dysfunction. Randomized trials show clear benefits for sexual function, muscle mass, and strength in these patients.

But testosterone is also increasingly marketed as a lifestyle enhancer.

“More and more men are taking testosterone supplements, in part because of greater awareness of hypogonadism in men, but also because of increased marketing and social media trends, particularly targeted at younger men,” said Emily Morbey, a PhD student at Cambridge and the study’s lead author. “When there is a medical need to boost testosterone, the benefits are likely to outweigh the risks, but this might not necessarily be the case when taken to boost performance.”

This could be a problem.

In the United States, the U.S. Food and Drug Administration has required warnings about potential cardiovascular risks linked to testosterone therapy. Labels now advise patients and clinicians to weigh those risks carefully. In the United Kingdom, no national guidance addresses cardiovascular risk from high testosterone levels.

Ken Ong, a senior author on the study, says that gap deserves attention. “Our results suggest there’s a need for more consistent warnings,” he said.

The study does not claim that testosterone therapy inevitably harms the heart. Genetic analyses reflect lifelong exposure, not the effects of a prescription taken for years or decades. Large clinical trials have produced mixed results, and some have found no increase in major cardiovascular events.

Still, the new findings add weight to a growing concern: testosterone is not a simple vitality hormone. It shapes blood pressure, metabolism, and now (more convincingly) the health of the heart itself.

For men considering testosterone outside clear medical need, the message from their DNA is sober. Strength may come with strings attached.