Researchers led by Jie V. Zhao, Yitang Sun, Junmeng Zhang, and Kaixiong Ye from the University of Hong Kong and the University of Georgia examined whether phenylalanine and tyrosine, two amino acids involved in metabolism and brain function, are connected to lifespan (lifespan). Their results point to a notable difference between men and women. Higher tyrosine levels were associated with shorter life expectancy in men, while no significant effect was detected in women.

The findings could eventually help scientists better understand why aging and longevity differ between the sexes, although much more research is needed before the results can be translated into health recommendations.

The research was published in Aging-US titled "The role of phenylalanine and tyrosine in longevity: a cohort and Mendelian randomization study."

Why Tyrosine Matters

Amino acids are the molecular building blocks that the body uses to make proteins. Phenylalanine and tyrosine are both found in foods that contain protein, and they are also available in dietary supplements.

Beyond their role in protein production, these amino acids participate in important biological processes. Tyrosine is especially interesting because the body uses it to produce neurotransmitters such as dopamine. Neurotransmitters are chemical messengers that allow nerve cells to communicate, and dopamine helps regulate functions that include mood, motivation, and thinking.

Despite these important roles, scientists still do not fully understand how long-term differences in phenylalanine and tyrosine levels might influence aging.

More Than 270,000 People Studied

To investigate, the researchers analyzed information from more than 270,000 participants in the UK Biobank, a large research database containing health and genetic data from people in the United Kingdom.

The team used two complementary approaches. First, they looked for associations between blood concentrations of phenylalanine and tyrosine and outcomes related to death and predicted lifespan. They also used genetic methods to investigate whether the relationships might go beyond a simple association.

One of those approaches was Mendelian randomization. This method uses naturally occurring genetic differences among people as a way to test whether a particular biological factor may contribute to an outcome. Because genes are assigned before many lifestyle choices and diseases develop, the technique can sometimes provide stronger clues about cause and effect than an observational study alone.

At first, higher levels of both amino acids appeared to be associated with an increased risk of death. But when the researchers examined the relationships more closely, tyrosine was the one that consistently stood out.

Tyrosine Linked to a Shorter Lifespan in Men

The genetic analyses suggested that elevated tyrosine levels may have a potentially causal relationship with reduced life expectancy in men. According to the researchers' estimates, higher tyrosine could shorten male lifespan by nearly one year.

The same pattern was not seen in women. Researchers found no significant effect of tyrosine on female lifespan.

The relationship also remained after the researchers accounted for phenylalanine and other related factors, strengthening the possibility that tyrosine itself may have an independent connection to aging.

The team also found that men generally have higher levels of tyrosine than women. That difference could potentially contribute to the well-documented gap in average lifespan between the sexes, although the findings do not establish that tyrosine is responsible for that gap.

"Phenylalanine showed no association with lifespan in either men or women after controlling for tyrosine."

Why Might Tyrosine Affect Longevity?

Scientists do not yet know exactly why higher tyrosine levels might be associated with shorter lives in men.

One possible explanation involves insulin resistance. This occurs when cells become less responsive to insulin, the hormone that helps control blood sugar. Insulin resistance is associated with several diseases that become more common with age and could therefore provide one possible link between tyrosine and longevity.

Tyrosine is also used by the body to make neurotransmitters involved in the stress response. Hormones and related signaling pathways can function differently in men and women, which could help explain why the apparent lifespan effect emerged only in men.

These mechanisms remain hypotheses, however, and will require further investigation.

What the Findings Mean for Tyrosine Supplements

Tyrosine is widely sold as a dietary supplement and is often promoted for improving focus, alertness, and mental performance. The new findings therefore raise questions about whether chronically high tyrosine levels could have unintended long-term consequences.

Importantly, the researchers did not directly test tyrosine supplements. The results therefore do not show that taking a tyrosine supplement shortens lifespan.

Instead, the study examined tyrosine levels in the body and their relationship with longevity. The researchers suggest that people with unusually high tyrosine concentrations could potentially benefit from dietary changes designed to lower those levels.

One possible strategy is restricting protein intake, which could reduce tyrosine exposure. However, it remains unclear whether deliberately lowering tyrosine through diet would actually extend lifespan or improve health.

More research will be needed to confirm the results, uncover the biological mechanisms involved, and determine whether diet or lifestyle changes can safely alter tyrosine levels in ways that promote healthier aging.