The drug finasteride, already used to treat hair loss and enlarged prostates, could also help to cut the risk of heart disease.

In an analysis of data from both male humans and mice, the drug was shown to improve health and reduce levels of cholesterol.

Too much cholesterol in the body is well known to increase heart disease risk, as it encourages atherosclerosis: fatty deposits in blood vessels, blocking the flow of blood through the arteries. Eventually, that can lead to strokes or heart attacks.

The research team, from the University of Illinois Urbana-Champaign and the University of Maryland, wanted to study the link between finasteride and heart disease because the drug works by putting a block on a protein that activates the hormone testosterone – and testosterone and atherosclerosis have tentatively been linked before.

The study used records in the National Health and Nutrition Examination Survey database collected between 2009 and 2016. Focussing on 155 male adults aged 50 or older, the team uncovered a relationship between cholesterol levels and the use of finasteride. Being a relatively small sample size, with records providing no indication of how long each person had been taking the drug for, the conclusions provide a weak but intriguing suggestion of finasteride's potential heart benefits.

"When we looked at the men taking finasteride in the survey, their cholesterol levels averaged 30 points lower than men not taking the drug," says food scientist Jaume Amengual, from the University of Illinois Urbana-Champaign.

The researchers also ran more comprehensive tests in mice genetically engineered to be predisposed to atherosclerosis, experimenting with three different levels of finasteride and a control group not given the drug. The mice were also fed a high calorie diet over the course of 12 weeks.

At the highest dose of 1,000 milligrams per kilogram of food, there were signs of health benefits in the animals, despite the poor quality of their diet. These signs included reductions in cholesterol.

"Mice that were given a high dose of finasteride showed lower cholesterol levels within the plasma as well as in the arteries," says University of Illinois Urbana-Champaign food scientist Donald Molina. "There were also fewer lipids and inflammatory markers in the liver."

It's important to note that the mice were given more finasteride relative to their size (approximately 2.5 mg daily for those on the highest dose) than the 1 or 5 milligram doses humans are usually prescribed to take each day. However, that the results were consistent across mice and human subjects is promising.

The next step for the research is a more detailed look at cholesterol levels in more diverse groups of people taking finasteride, or clinical trials – but the fact that it's already an approved drug should help speed up the process.

"Over the past decade, doctors have started prescribing this drug for individuals transitioning either from male to female or female to male," says Amengual. "In both cases, the hormonal changes can trigger hair loss."

"The interesting thing is that transgender people are also at a higher risk of cardiovascular diseases. So this drug could have a potential beneficial effect to prevent cardiovascular disease not only in cis men, but also in transgender individuals."

The research has been published in the Journal of Lipid Research.