“Testosterone replacement therapy is anti-aging”

Does TRT age you faster, or help you live longer? Neither has been shown. The largest attempt to settle it pooled 35 placebo-controlled trials covering 5,601 men and found too few deaths across all of them to assess mortality at all [2]. Nobody knows, in either direction.

The same synthesis answered a narrower question. Heart attacks, strokes and related events reached 120 of 1,601 men on testosterone and 110 of 1,519 on a dummy treatment, about 8 in 100 against about 7 in 100, a gap small enough to be chance [2].

Who was studied matters here. Every trial enrolled men with hypogonadism, the medical term for a testosterone deficiency confirmed by blood test: two fasting readings below 300 nanograms per decilitre, the unit a laboratory prints testosterone in, alongside symptoms [1].

The largest safety trial, TRAVERSE, gave testosterone gel or a dummy gel to 5,246 men aged 45 to 80 with that confirmed deficiency plus heart disease or a high risk of it, and followed them for about three years [1]. A heart attack, stroke or heart-related death reached 182 men on testosterone (7.0%) and 190 on the dummy gel (7.3%) [1]. Three problems were more common on testosterone: irregular heart rhythm, sudden kidney injury, and blood clots in the lungs [1].

The anti-ageing case leaned hardest on bone, and that is where it broke. Testosterone raises bone density, so counting fractures looked like a formality. Among 5,204 of those men followed for a median of just over three years, a bone was broken by 91 of the 2,601 on testosterone and 64 of the 2,603 on the dummy gel: 3.50% against 2.46%, or roughly 35 men per 1,000 against 25 [3]. Every other fracture measure the trial counted pointed the same way [3]. Denser bone did not mean fewer breaks.

Is TRT a lifelong treatment? For most men who start it for a confirmed deficiency, yes - it replaces a hormone the body is not making, and it does not teach the body to make it again.

Supplied testosterone actively suppresses whatever is left. A review of testosterone therapy and sperm production in Nature Reviews Urology describes how it switches off the pituitary signals that drive the testicles, cutting both the body's own output and the much higher concentration of testosterone held inside the testicles, which in turn impairs sperm production. Stopping does not leave a man further ahead than before he started, because the deficiency that justified the prescription is still there. Sperm production usually resumes afterwards, on a timetable that same review calls highly variable, which is why it lists testosterone as contraindicated for men who are trying to conceive.

What happens after that is not in the trials, because none of them ran long. Men in TRAVERSE used the gel for about 22 months on average [1], and the 35-trial synthesis closes by calling for long-term safety evidence that still does not exist [2]. Men are being asked to take a hormone indefinitely on roughly three years of evidence.

What testosterone does deliver for men who qualify is narrower than the marketing. Across almost every subgroup of the 35 trials it improved sexual function and quality of life, and it lowered cholesterol, triglycerides and haemoglobin, the protein in red blood cells that carries oxygen [2]. Correcting a deficiency is not the same thing as slowing ageing.

The evidence does not describe:

• men whose testosterone sits in the normal range and is drifting down with age, who were enrolled in none of these trials, so the benefit side of their ledger is blank
• men without heart disease or a high risk of it, which is not the population TRAVERSE was built around [1]
• anyone treated for longer than the trials ran [1][2]
• women, and men under 45 [1]

Testosterone is prescription medicine with a genuine use, and starting, continuing or stopping it is a decision for a doctor who has run the blood test twice. Clinics that prescribe it for tiredness without confirming a deficiency hand out the risks TRAVERSE measured without the benefits that came attached. That is why this claim lands as partially supported: sound treatment for a confirmed deficiency, an unproven bet on ageing for everyone else.