Testosterone levels may influence the risk of developing an irregular heartbeat, but the relationship appears more complicated than simply having too little or too much of the hormone. Testosterone plays an important role in sexual function, muscle mass and bone health, and men with a confirmed deficiency may receive replacement therapy. However, researchers are increasingly examining whether changes in testosterone levels could also affect the heart’s electrical activity.
A narrative review published in the Journal of the Endocrine Society, led by Anand Reddy Maligireddy of the University of Kansas Medical Center, examined evidence from human studies and laboratory experiments. The authors found that both low and high testosterone levels have been associated with atrial fibrillation, a common heart rhythm disorder. However, the available evidence does not establish that testosterone directly causes the condition.
Atrial fibrillation, also known as AF or AFib, occurs when the heart’s upper chambers beat in a rapid, disorganized rhythm instead of contracting normally. Some people experience palpitations, fatigue or dizziness, while others have no noticeable symptoms. The condition increases the risk of stroke, heart failure and other complications, and many patients require long-term anticoagulant medication to reduce their risk of stroke.
What the new review found
The review highlights observational studies suggesting that men with lower testosterone levels may face a greater risk of developing atrial fibrillation over time.
For example, analyses from the long-running Framingham Heart Study have linked lower testosterone concentrations with an increased likelihood of atrial fibrillation in certain age groups. Such studies follow participants over extended periods, allowing researchers to identify associations between hormone levels and subsequent health outcomes.
However, observational findings cannot establish whether low testosterone contributes directly to irregular heart rhythms or reflects other underlying health problems.
At the opposite end of the spectrum, some evidence suggests that unusually high testosterone levels may also be associated with increased risk.
One analysis involving 4,570 older men without known cardiovascular disease found that participants in the two highest testosterone groups had approximately twice the risk of developing atrial fibrillation compared with those whose hormone levels were in the middle range.
During a median follow-up of 4.4 years, 286 participants developed atrial fibrillation.
Interestingly, the same study did not identify a statistically significant increase in risk among men with the lowest testosterone levels compared with the middle group.
This difference illustrates the inconsistencies in the available evidence and highlights why researchers remain cautious about defining specific testosterone concentrations as either protective or harmful.
Insights from testosterone therapy trials
To investigate whether changing testosterone levels influences cardiovascular risk, researchers have also examined randomized clinical trials of testosterone replacement therapy.
The largest of these is the TRAVERSE trial, published in 2023, which enrolled 5,246 men with low testosterone levels and either established cardiovascular disease or multiple cardiovascular risk factors.
Participants were randomly assigned to receive testosterone gel or a placebo gel.
Over a median follow-up of 33 months, testosterone therapy did not increase the risk of the trial’s primary composite outcome, which included cardiovascular death, nonfatal heart attack and nonfatal stroke.
However, atrial fibrillation occurred more frequently among men receiving testosterone.
The condition was reported in 3.5 percent of participants treated with testosterone, compared with 2.4 percent of those receiving placebo.
The testosterone group also experienced slightly higher rates of pulmonary embolism and acute kidney injury.
Nevertheless, not all research has found a consistent association between testosterone treatment and atrial fibrillation.
A 2024 systematic review and meta-analysis combining 106 randomized controlled trials did not identify a statistically significant overall increase in atrial fibrillation when results from TRAVERSE were considered alongside those from smaller studies.
Many of these trials involved fewer participants and shorter follow-up periods, potentially limiting their ability to detect relatively uncommon cardiovascular events.
Together, these findings suggest that the relationship between testosterone therapy and heart rhythm disturbances remains uncertain and requires further investigation.
Possible biological mechanisms
Laboratory and animal studies offer possible explanations for why testosterone concentrations at either end of the spectrum might influence heart rhythm.
The review notes that low testosterone may affect the regulation of calcium within heart muscle cells.
Calcium movement is essential for the electrical and mechanical processes that coordinate each heartbeat. Disruptions in calcium handling can interfere with normal cardiac signaling and potentially contribute to abnormal rhythms.
At higher testosterone concentrations, other electrical pathways may become involved.
Some experimental findings suggest that testosterone can alter potassium currents across heart cell membranes. These currents play an important role in repolarization, the process through which heart cells restore their electrical state after each heartbeat.
Changes in potassium signaling may increase electrical instability in cardiac tissue, potentially making certain arrhythmias more likely.
However, these proposed mechanisms have not been conclusively established in humans.
Their effects may also depend on age, existing cardiovascular disease, genetic characteristics and interactions with other hormones.
The researchers emphasize that testosterone operates within a complex network of endocrine and cardiovascular processes. Its relationship with heart rhythm is therefore unlikely to be explained by a single hormone measurement.
Implications for men considering treatment
The findings raise important considerations for men who are receiving testosterone replacement therapy or considering starting treatment.
Current clinical guidelines generally recommend testosterone therapy for men who have symptoms consistent with deficiency and repeatedly confirmed low blood testosterone levels.
The review does not suggest that appropriately prescribed treatment should be avoided. Instead, it emphasizes the importance of considering potential heart rhythm risks when discussing the benefits and disadvantages of therapy.
Before prescribing testosterone, clinicians should assess a patient’s overall cardiovascular health, including blood pressure, cholesterol levels, diabetes and any history of heart disease or stroke.
Other established risk factors for atrial fibrillation, including obesity, excessive alcohol consumption and obstructive sleep apnea, should also be evaluated and managed when appropriate.
Excess body fat is closely associated with lower testosterone concentrations, creating a complex relationship between metabolic health and hormone regulation.
Lifestyle changes involving weight management, regular physical activity and improved sleep may benefit both testosterone levels and cardiovascular health.
For some men, addressing these underlying factors may also reduce the need for testosterone treatment or influence the most appropriate therapeutic approach.
Why the evidence is still uncertain
Despite increasing scientific interest, several important questions remain unanswered.
Observational studies can identify associations between testosterone concentrations and atrial fibrillation, but they cannot determine whether hormone levels directly influence the development of the condition.
Underlying illnesses, medication use, metabolic disorders and other factors may affect both testosterone concentrations and cardiovascular risk.
Randomized trials such as TRAVERSE provide stronger evidence about the effects of testosterone therapy, but they also have limitations.
Participants are often older men with established cardiovascular conditions or specific risk factors. Consequently, the findings may not apply equally to younger men or those with borderline testosterone levels.
Furthermore, many clinical trials are primarily designed to evaluate major cardiovascular events rather than less frequent rhythm disturbances.
Another complication is that testosterone is only one component of the body’s androgen system.
Related hormones, the conversion of testosterone into estrogen and individual differences in androgen receptor activity may all influence cardiovascular responses.
Future studies will need to examine how these biological pathways interact and whether they help explain differences in atrial fibrillation risk between individuals.
Looking ahead to personalized targets
The review’s authors suggest that testosterone concentrations near the middle of the normal physiological range might be associated with a more favorable heart rhythm risk profile than levels at either extreme.
However, they emphasize that this remains a hypothesis rather than an established treatment recommendation.
No randomized clinical trial has demonstrated that adjusting testosterone therapy to maintain a narrowly defined target range reduces the risk of atrial fibrillation.
For now, individualized treatment remains essential.
Men with persistent symptoms and confirmed testosterone deficiency may benefit from replacement therapy, but potential risks should be discussed before treatment begins.
Regular monitoring may include testosterone measurements, blood counts, prostate-related assessments when appropriate and heart rhythm evaluation in patients with relevant symptoms or risk factors.
Researchers are also awaiting additional evidence from ongoing and future studies examining the long-term cardiovascular effects of testosterone therapy in more diverse populations.
As these findings emerge, clinical guidelines may become more precise about treatment targets, dosing strategies and the coordination of endocrine and cardiovascular care.
Overall, the review published in the Journal of the Endocrine Society suggests that testosterone should not be viewed as either universally protective or inherently harmful to the heart.
Instead, the available evidence points toward a potentially complex relationship in which both deficiency and excess may be associated with cardiovascular risks. Determining whether an optimal range exists, and whether maintaining it can prevent atrial fibrillation, will require further clinical research.
