Tyrosine, a non-essential amino acid, is popularly enjoyed as a supplement (usually in the form of n-acetyl l-tyrosine, or “NALT” to its friends) with the intention of boosting dopamine levels (tyrosine is a precursor of dopamine, meaning the body can use it to make dopamine, and dopamine is necessary for an assortment of cognitive functions and also, often forgotten, motor functions).

Does it work? Yes, if and only if dopamine levels were low and the reason dopamine levels were low was because of a shortage of the ingredients. Otherwise, probably not.

We wrote more about that here: The Dopamine Precursor And More

However, beyond supplements, it is also found in most protein-containing foods, and is found most abundantly in meat and dairy products (because those animals, just like humans, were capable of synthesizing it from its precursor phenylalanine, which is found in many plants).

However, if we do not supplement tyrosine and we consume neither meat nor dairy, then our bodies will only synthesize as much as we need.

On the other hand, if we supplement tyrosine and/or we consume meat and/or dairy, then it is possible to end up with higher tyrosine levels.

And that’s what we’re going to be looking at the science of, today:

Beyond “non-essential”

Researchers (Dr. Jie Zhao et al.) analyzed data from 272,475 participants in the UK Biobank to examine whether blood levels of phenylalanine and/or tyrosine were linked to lifespan.

About those participants:  of the 272,475 participants, 14,230 men’s deaths were recorded, and 9,734 women’s deaths.

So, what did they find?

Initial findings re phenylalanine: after adjusting for confounders, phenylalanine was associated with a slightly higher risk of all-cause mortality overall with similar results in men and women, but (plot twist!) this association disappeared after controlling for tyrosine in genetic analyses.

Initial findings re tyrosine: higher plasma tyrosine was associated with higher all-cause mortality overall and in men with a hazard ratio of 1.03 per standard deviation increase, but not in women where the hazard ratio was 1.00 (a hazard ratio of 1.00 means it is 1x as likely as otherwise, i.e., no change).

Now, that may not sound like a big difference, but it’s a big difference if you die, so let’s take a close look at the stats:

Mendelian randomization analysis shows that:

• higher tyrosine levels in women were linked to a reduction of 0.91 years of life with high statistical significance
• higher tyrosine levels in women were not significantly associated with any reduction in lifespan; the data did suggest there may be a slight reduction for women too, though _{(but the association was so weak that we’re effectively talking about the Plato’s cave of data here; it’s a shadow of a shadow, whereas for men it was a clearly smoking gun, for women it was more like a few possible smoke particles in the air that might just turn out to be dust).}

Why the sex differences?

It’s not known for sure, but Dr. Zhao and her team highlight that tyrosine is involved in producing neurotransmitters such as dopamine and norepinephrine, and plays a role in not just stress-related brain chemistry, but also otherwise seemingly unrelated systemic effects such as insulin resistance (which differs by sex), this may explain the difference in life expectancy reduction—since insulin resistance is a major driver of metabolic syndrome.

For more on that, see: Why We Get Sick – by Dr. Benjamin Bikman

This is consistent, by the way, with previous studies* done in Drosophila melanogaster a few years ago, so if ever you wonder “are these animal studies really indicative and what is the point in studying fruit flies?”, then the answer is yes, they can be, and D. melanogaster is particularly useful for studies pertaining to longevity.

*Like this one: Sensing of the non-essential amino acid tyrosine governs the response to protein restriction in Drosophila ← short version is that restricting their tyrosine intake caused them to live longer

And as for this study we’ve been looking at today, you can read it in full here: The role of phenylalanine and tyrosine in longevity: a cohort and Mendelian randomization study

Want to learn more?

For a much deeper dive into the broadly inversely proportional relationship between meat consumption and longevity, you might like:

The China Study – by Dr. T Colin Campbell and Dr. Thomas M. Campbell

Take care!