Older men may want to think twice before starting testosterone treatment, based on results of a clinical trial that found testosterone speeds up the development of plaque in the heart’s arteries.

Published in the Journal of the American Medical Association, this study looked at the association between testosterone treatment and plaque build-up in older men. It was conducted in response to recent studies that have raised concerns about the impact of testosterone therapy on heart health.

Some studies have found that testosterone treatment may increase risk for heart events like heart attack and stroke, while others have found no relationship. With a ten-fold increase in testosterone sales in the United States from 2000–2011, experts worry about the potential impact of widespread testosterone use on heart health.

For this reason, researchers conducted the Testosterone Trials, which investigated the effects of testosterone treatment in elderly men with low testosterone. The studies looked at multiple outcomes, such as sexual function, brain function, vitality and cardiovascular risk.

The heart-related trial was conducted from 2010–2014 and included 170 men aged 65 years or older with low testosterone. For one year, half of participants were randomly assigned to active testosterone treatment—a topical gel applied to the arms and shoulders daily—while half received a placebo gel with no active ingredients.

At the start and end of the study, participants underwent a test called coronary computed tomographic angiography, which uses CT imaging to measure plaque build-up in the heart. Plaque build-up is dangerous because it narrows the heart’s arteries and is associated with increased risk for heart disease—the leading killer of Americans.

After analysis, researchers found that men taking testosterone had a greater increase in non-calcified plaque volume during the study period compared to men using the placebo gel. In fact, on average men taking testosterone had a 41mm3 greater increase in plaque volume than those taking the placebo, and this difference was considered statistically significant.

While findings suggest testosterone treatment accelerates plaque build-up in older men, authors do note certain limitations. The study only followed participants for one year, which is a relatively short time period. It also did not assess the impact of plaque build-up on outcomes like heart attack and death, so it’s unknown whether testosterone treatment impacts long-term health outcomes.

However, the study still raises concerns about the safety of testosterone treatment in older men with low testosterone. As a result, experts suggest that patients considering testosterone therapy discuss the risks and benefits with their doctor before making any decisions about testosterone treatment. They also encourage further research on the issue to better understand the association between testosterone treatment and heart health in older men.