Both Low & High Levels Of Testosterone Raise This Cardiac Risk For Men

Testosterone replacement therapy (TRT) is becoming increasingly popular for men of all ages, with the general assumption being that higher levels of testosterone are always better. This comes as no surprise given all the benefits men report when starting TRT: increased energy, a sharpened mind, and better performance in the gym and the bedroom.

But a new review in the Journal of the Endocrine Society is questioning that "more is always better" assumption, specifically when it comes to how testosterone levels relate to atrial fibrillation (AFib), the most common type of irregular heartbeat. Interest in this question was heightened by the Cardiovascular Safety of Testosterone-Replacement Therapy1 trial, a large safety study that reassured doctors TRT doesn't raise the risk of heart attack or stroke, but did flag a higher rate of AFib among men on testosterone therapy compared to those on a placebo. This review pulled together the existing research to dig into what's actually driving that AFib finding.

What the research says

You may expect the study to have found a direct relationship between testosterone and Afib risk, with more testosterone always indicating increased risk, but this study actually pointed to a U-shaped relationship: Both low and high testosterone levels were associated with an increased risk of atrial fibrillation, while men with mid-range levels had the lowest risk.

Supporting research backs this up from both ends. In an analysis of the ASPREE study2, older men with the highest testosterone levels showed a notably elevated risk of developing AFib compared to those in the middle range. On the other end, an analysis of over 173,000 men in the UK Biobank3 found that low testosterone was also linked with a greater risk of arrhythmias.

In other words, this isn't a story about testosterone therapy being inherently risky. It's a story about balance. Having too little and too much testosterone each appear to carry their own cardiac risks.

Why both extremes may stress the heart

The heart's electrical system relies on a delicate balance to keep its rhythm steady, and hormones play a role in that balance. Studies have found that estrogen has a protective effect on the heart, and testosterone seems to play a role as well.

When levels drop too low, the body may lose some of the protective cardiovascular effects that healthy testosterone levels normally provide. On the other end, pushing levels too high (which can happen when TRT is poorly monitored or acquired from the gray market) may place extra strain on the heart's structure and electrical signaling.

This U-shaped framework also helps make sense of the TRAVERSE trial's AFib finding. Rather than suggesting TRT itself is dangerous for the heart, it points to poor dosing and monitoring as the more likely culprits. The goal isn't to avoid testosterone therapy altogether, but to avoid the extremes.

How to stay in the testosterone sweet spot

If you're on TRT or considering it, this research underscores why working closely with a doctor matters more than chasing a specific number on a lab report. A few things to keep in mind...

The takeaway

Testosterone's relationship with heart rhythm comes down to balance, not maximizing. If you're on TRT or thinking about starting it, book the bloodwork and keep your doctor in the loop, that's the clearest path to the benefits without the added cardiac risk.