Testosterone and Your Heart: Why Too Little and Too Much May Both Raise Rhythm Risks

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A "U-Shaped" Risk Pattern

Researchers at the Kansas City Veterans Affairs Medical Center reviewed existing studies on testosterone and atrial fibrillation (AF), an irregular and often rapid heartbeat. The review appeared in September 2026 in the Journal of the Endocrine Society. It covered research published through early May 2026.

The authors describe a "U-shaped" pattern. Men at either end of the testosterone scale, too low or too high, showed more AF. Risk appeared lowest in the middle, with total testosterone around 350 to 550 nanograms per deciliter (ng/dL, the standard unit for blood testosterone).

Senior author Dr. Rajat Barua said that both extremes seem to raise risk through separate biological mechanisms, so "the dose and the target level matter."

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Why Atrial Fibrillation Matters

AF can cause palpitations and fatigue, but the greater danger is stroke. Barua notes that the condition often requires lifelong blood-thinning medication.

Testosterone therapy is widely prescribed to middle-aged and older men. That makes the question of how much is too much relevant to a large group of patients.

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What the Evidence Shows

The review draws on several kinds of evidence:

• Large population studies found more AF in men with low testosterone and in men with high-normal levels. In one analysis of older men, AF risk was nearly double in the highest testosterone groups compared with the middle range.
• Laboratory research since 2025 suggests that low and high testosterone disturb heart cells in different ways.
• Imaging and mechanistic work hints that testosterone exposure may also change the structure of the heart's left atrium (an upper chamber).

The most important clinical data come from the TRAVERSE trial, published in the New England Journal of Medicine in 2023. It enrolled 5,246 men aged 45 to 80 with low testosterone and existing or high risk of heart disease. Half received a daily testosterone gel and half a placebo gel.

The trial's main result was reassuring. Testosterone therapy did not increase major cardiac events such as heart attack or stroke compared with placebo. However, AF occurred in 3.5% of treated men versus 2.4% on placebo. Pulmonary embolism (a blood clot in the lungs) and acute kidney injury were also more common in the treated group.

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Important Limits

The authors are cautious. The review does not establish that testosterone therapy causes AF, and the evidence is described as conflicting. It is a review of earlier studies, not a new clinical trial, and it received no external funding.

Open questions remain. These include whether different formulations, treatment length, or "free" testosterone (the portion not bound to proteins in the blood) change the risk.

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What This Means for Patients

The authors recommend treatment that is individualized and monitored. In their view, doctors should aim to bring testosterone back to the middle of the normal range rather than push it to the upper end.

Epocrates' summary of the review adds that doctors should watch for AF risk factors and rhythm problems, especially in older men with other heart conditions. TRAVERSE's findings also apply only to men with documented low testosterone, not to men taking it for general vitality.

Men considering or already on therapy should discuss their personal heart risk with a doctor and agree on a monitoring plan.

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Outlook

The review adds to a long debate over testosterone therapy. Larger and longer studies will have to show whether keeping levels in the mid-range actually prevents AF. Until then, the practical message is balance. More testosterone is not automatically better, and a deficiency should not go unexamined either.

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Sources

1. Endocrine Society news release, "Review links low and high testosterone to atrial fibrillation risk": https://www.eurekalert.org/news-releases/1141743
2. HealthDay (via MedicineNet), "High Testosterone Increases Risk Of Heart Rhythm Disorder, Review Finds," Sept. 1, 2026: https://www.medicinenet.com/high_testosterone_increases_heart_rhythm_risks/news.htm
3. Epocrates, "Testosterone may raise AF risk at both extremes": https://www.epocrates.com/online/article/too-much-or-too-little-testosterone-may-raise-af-risk-at-both-extremes
4. Medical Dialogues, "Testosterone Levels Linked to Heart Rhythm Changes, With Risks at Both Extremes": https://medicaldialogues.in/mdtv/cardiology/videos/testosterone-levels-linked-to-heart-rhythm-changes-with-risks-at-both-extremes-study-178574
5. Maligireddy AR, Barua ST, Barua RS, "Association of testosterone and testosterone replacement therapy with atrial fibrillation: an updated review," Journal of the Endocrine Society 10(9):bvag180: https://doi.org/10.1210/jendso/bvag180
6. Lincoff AM et al., "Cardiovascular Safety of Testosterone-Replacement Therapy," N Engl J Med 2023;389:107-117 (abstract): https://www.ovid.com/journals/nejm/pdf/10.1056/nejmoa2215025~cardiovascular-safety-of-testosterone-replacement-therapy
7. The Hospitalist, "Big trial reassures on heart safety of testosterone in men": https://blogs.the-hospitalist.org/content/big-trial-reassures-heart-safety-testosterone-men

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