A Study Tied Higher Tyrosine Levels to Shorter Lifespan in Men — With Big Caveats

A study of more than 270,000 UK Biobank participants has linked higher blood levels of tyrosine — an amino acid widely sold as a “brain” supplement for focus and alertness — to reduced life expectancy in men, with no significant effect in women. The researchers, from the University of Hong Kong and the University of Georgia, are unusually direct about what the finding does not mean.

What tyrosine is

Tyrosine is not exotic. It is a non-essential amino acid the body makes from phenylalanine and also obtains from protein in the diet, and it serves as the precursor for dopamine, noradrenaline and adrenaline, as well as for thyroid hormones. That neurotransmitter role is the basis of its marketing: supplement products position it as supporting alertness, focus and performance under stress.

Blood levels vary naturally between individuals, and notably, men have higher concentrations than women on average — relevant to how the study’s central result should be read.

What the study did

The work, published in Aging-US, combined two approaches. An observational analysis examined whether measured blood amino acid levels tracked with mortality across the cohort. Initially, elevated levels of both tyrosine and another amino acid appeared connected to increased mortality risk.

The team then applied Mendelian randomisation, a genetics-based technique. It uses inherited genetic variants that influence a trait — here, tyrosine levels — as a natural experiment. Because those variants are allocated at conception rather than by lifestyle, the method can partially separate causation from the confounding that plagues observational nutrition research.

That analysis found tyrosine independently showed a potentially causal relationship with reduced life expectancy in men — on the order of nearly one year. In women, no significant effect appeared.

The caveat the researchers put first

This is the part most coverage of studies like this gets wrong, so it is worth quoting the position directly: the results “do not show that taking a tyrosine supplement shortens lifespan.”

The study examined naturally occurring blood concentrations. No supplement was administered, no supplemented group was followed, and no dose-response relationship for supplementation was established. Naturally elevated tyrosine may reflect an underlying metabolic state; deliberately raising it with a capsule is a different exposure, and the study is silent on it. The researchers suggest only that people with unusually high concentrations might potentially benefit from dietary changes to lower them — and note it remains unclear whether deliberately lowering tyrosine would extend life at all.

Two proposed mechanisms, both untested

The first is insulin resistance. This is the more plausible of the two, because it connects to an established body of metabolomics work: elevated aromatic and branched-chain amino acids have been repeatedly associated with insulin resistance and with later development of type 2 diabetes. On that reading, high tyrosine may be a marker of metabolic dysfunction rather than a cause of harm itself.

The second involves tyrosine’s role in producing stress-response neurotransmitters, with the pathways operating differently between the sexes — a candidate explanation for the male-specific finding. Both mechanisms remain hypotheses.

What Mendelian randomisation cannot fix

The method is a genuine improvement on plain observation, but it carries its own assumptions. Genetic variants can influence more than one trait, so an apparent effect may run through a different pathway than assumed. The technique also estimates the effect of lifelong genetically determined exposure, which is not the same as the effect of changing a level in adulthood.

The UK Biobank has its own well-documented limitation: participants are healthier, wealthier and less ethnically diverse than the general UK population, which can distort associations.

What would have to happen for this to matter clinically

It is worth being concrete about the distance between this result and any change in practice, because single-biomarker longevity findings appear constantly and almost none of them travel.

The first requirement is replication in independent cohorts with different demographics, since a UK Biobank finding could reflect features of that specific population. The second is a demonstrated dose-response relationship — if tyrosine genuinely shortens life, more of it should be worse in a graded way. The third, and the only one that would truly settle it, is an interventional study showing that deliberately lowering tyrosine in people with high levels changes an outcome that matters. No such trial exists, and the researchers themselves note it is unclear whether lowering tyrosine would extend lifespan at all.

Until at least the first two are met, the appropriate response to a headline about an amino acid and lifespan is interest, not action.

The honest takeaway

An early signal worth studying — not evidence that a tyrosine supplement is harmful, and not a reason for anyone to have their amino acid levels measured.

The wider point is about the supplement category rather than this molecule. Amino acid products are sold on mechanistic plausibility — tyrosine makes dopamine, dopamine supports focus, therefore more tyrosine is better — a chain of reasoning that is rarely tested end to end. In most markets supplements are regulated as foods rather than medicines, so the burden of proof before sale is far lighter than for a drug. That asymmetry, not this particular result, is the reason for caution. This summarises research and is not medical advice.