Taurine and Biological Age: Part Two: The Challenge

Abstract

Part One set out the hypothesis: taurine falls by more than 80 per cent across the human lifespan, and restoring it slows ageing in animals. The first claim is the load-bearing one, because it is the only part of the argument that concerns humans directly.

In August 2025, a group working across Montreal published a short communication in Aging Cell under a title that leaves nothing to interpretation: "Experimental Evidence Against Taurine Deficiency as a Driver of Aging in Humans".

They measured serum taurine in 137 men aged 20 to 93 and found no association with age, with muscle, with physical performance, with insulin sensitivity, or with mitochondrial function. This part is about how they looked and what that means.

1.How to Test a Driver

Vincent Marcangeli, Marina Cefis and Gilles Gouspillou set out their reasoning before their data, which is the right order.

If taurine deficiency drives human ageing, then circulating taurine should progressively decline through adulthood, and it should track the things that decline alongside it — body composition, muscle mass, strength, physical function. They added two further predictions: it should correlate with markers of insulin sensitivity, and plausibly with mitochondrial health, since mitochondrial dysfunction is the mechanism the original paper proposed.

These are falsifiable predictions derived from someone else's hypothesis. That is a more useful contribution than another positive mouse study.

2.The Cohort

The analysis drew on 137 men aged 20 to 93 — 49 classified as physically inactive and 88 as active — who had already undergone unusually deep phenotyping for a separate study.

Body and muscle composition were measured by dual-energy X-ray absorptiometry and peripheral quantitative computed tomography. Physical performance was assessed with four validated tests: six-minute walk, timed up and go, thirty-second sit-to-stand, and a step test. Strength and power were measured by dynamometry and a leg extensor power rig.

And they took vastus lateralis muscle biopsies, which is what makes this study hard to wave away. Mitochondrial respiration, reactive oxygen species production and calcium retention capacity were measured in permeabilised fibres from living muscle.

Serum taurine was quantified by isotope-dilution mass spectrometry with a deuterated internal standard, with intra-assay coefficients of variation below 3 per cent.

The cohort behaved as an ageing cohort should: muscle mass, strength, power and physical performance all declined with age, and physical activity conferred partial protection. The instrument was working.

3.What They Found

No association between serum taurine and age.

No correlation with the six-minute walk test, the timed up and go, or the thirty-second sit-to-stand. No association with muscle mass, strength, power or cross-sectional area. None with total lean or fat mass. None with HOMA-IR or QUICKI, the two standard indices of insulin sensitivity, nor with fructosamine, nor with C-reactive protein.

In the biopsies: no correlation with maximal mitochondrial respiration, none with hydrogen peroxide emission as a surrogate for reactive oxygen species, and none with mitochondrial calcium retention capacity.

One correlation did reach significance, and it ran the wrong way: higher taurine was associated with worse performance on the step test, which the authors describe as arguably the most discriminating physical measure in their battery.

Active and inactive participants did not differ in serum taurine either — 92.40 micromolar against 96.93, p equal to 0.338 — which is worth noting because the original paper had proposed exercise as a route to raising taurine.

4.Why This Is Not a Measurement Artefact

The obvious objection to a failed replication is that the second team measured badly. The authors close that door in one sentence: their serum taurine concentrations sat within the range reported by Singh and colleagues in humans.

Same molecule, same range, opposite conclusion about its relationship with age.

They also identify a specific weakness in the original human analysis, and it is the most important sentence in the paper. The reported correlation between taurine and age appeared to be driven mainly by individuals aged 20 and under, and participants over 65 were absent.

If that is right, the 80 per cent decline is not a description of ageing. It is a description of the difference between adolescents and adults, projected onto a lifespan that was not sampled at its upper end.

5.What the Study Does Not Show

The authors are careful here and we should be too.

This is a cross-sectional secondary analysis, not a trial. It shows that taurine concentration does not track ageing or function; it cannot show that giving people taurine does nothing. A molecule can be a poor biomarker and still be a useful intervention — the two questions come apart, and conflating them is a mistake in both directions.

The cohort is entirely male, which limits it. And the authors state explicitly that their findings do not rule out benefit from supplementation in older adults with genuinely low taurine, or in people with chronic disease.

They also record something we could not verify ourselves. While their manuscript was under review, Science published a paper by Fernandez and colleagues titled "Is taurine an aging biomarker?", which the Montreal team describe as challenging taurine's role in ageing and its utility as a biomarker in mice, non-human primates and humans. That paper is closed access with no legal open copy, so we have not read it and everything in this paragraph is reported at one remove.

What can be said without reading it: the journal that published the hypothesis in 2023 published a paper questioning it in 2025, and a reader encountering taurine marketing today is unlikely to be told either thing.

Editorial Comment

Taurine is in Boost at 500 mg. It is easier to write this part than it looks, because our 500 mg was never chosen on the strength of the ageing literature — but a company in our position would still normally leave a failed replication out.

The finding that matters here is not that taurine is useless. It is that the one human claim underpinning the entire longevity story — an 80 per cent lifetime decline — was not found by a group that went looking for it with muscle biopsies and mass spectrometry, and may have originated in a sample that stopped at 65.

Part Three takes up a third possibility: that both groups measured correctly, and the relationship between taurine and ageing is not a straight line at all.