Testosterone therapy alone won’t prevent type 2 diabetes in older men, Australian researchers find — but here’s what will

Testosterone treatment can make older men stronger and leaner, but it is not a shortcut to preventing type 2 diabetes – and Australian researchers are now saying the message is unambiguous: there is no substitute for a healthy lifestyle.

New findings from an Adelaide University-led trial, presented this week at the ENDO 2026 conference in Chicago, have found that while testosterone therapy delivered meaningful short-term benefits for blood sugar control in at-risk men aged 50 to 74, those benefits diminished significantly over four years when not combined with a weight loss and lifestyle program.

What the research found

The study is an extension of a major Australian trial involving more than 1,000 men across centres in Sydney, Melbourne, Perth, Brisbane and Adelaide. The original trial found that testosterone treatment combined with a healthy lifestyle program produced a 40 per cent reduction in type 2 diabetes risk after two years, compared to a placebo – a striking result that attracted significant attention.

In the follow-up study, a smaller group of 120 men continued for a further two years, taking either testosterone treatment or a placebo but without the lifestyle program component. Researchers wanted to understand what testosterone alone could achieve over the longer term.

The results were instructive. Testosterone treatment did continue to reduce body fat, improve muscle mass and strength, support blood glucose levels and improve sexual desire. Most of these improvements appeared early and were maintained.

But blood sugar control told a different story.

“In some older men, small benefits of testosterone did persist for up to four years,” said Adelaide University Professor Gary Wittert, Director of the Freemasons Centre for Men’s Health and Wellbeing. “However, when it came to blood sugar, the benefits were greatest early on, and by the four-year mark the proportion of men with diabetes in the testosterone treatment group increased and was similar to the placebo treatment group.”

In other words, without the lifestyle program running alongside it, testosterone treatment alone was not enough to hold the line against diabetes over the long term.

Why lifestyle remains non-negotiable

Professor Wittert is direct about what the findings mean for older Australian men.

“The most likely explanation for these findings is that testosterone is not a replacement for a healthy lifestyle and would need to be combined with a weight loss program for the best chance of preventing type 2 diabetes,” he said.

This matters because type 2 diabetes is one of the most prevalent chronic conditions in Australia. More than 1.2 million Australians are currently living with the disease, and men are more likely to be affected than women. The condition is strongly linked to abdominal obesity, poor diet and physical inactivity – all modifiable factors that respond to lifestyle change.

The growing availability of medications like Ozempic – which has attracted enormous public interest for its weight loss effects – makes the research particularly timely. Professor Wittert is measured but clear on that front too.

“Even with newer treatments for type 2 diabetes, like Ozempic, a healthy diet and both resistance and aerobic physical activity are necessary for the best overall health outcome,” he said.

The practical takeaway for men over 50

Perhaps the most actionable message from the research is one that does not require a prescription or a clinical trial: pay attention to your waist.

“One of the important messages from this research is to routinely measure waist circumference and consider metabolic health,” Professor Wittert said. “Optimising lifestyle-related health behaviours can improve testosterone levels, reduce fat, increase muscle and improve sexual function.”

That is a notable point. The research suggests the relationship between testosterone and lifestyle works in both directions – just as testosterone treatment alone cannot substitute for healthy habits, improving those habits can itself support healthy testosterone levels.

For men in their 50s, 60s and 70s who are concerned about diabetes risk, the evidence from this four-year Australian trial is consistent with everything researchers have found before it: strength training, aerobic exercise and a healthy diet remain the most reliable tools available. Testosterone therapy may play a supporting role for some men, but it works best alongside those fundamentals, not instead of them.