A large-scale study published in 2025 has found that high levels of glycine, an amino acid sold widely as a brain-boosting and sleep-enhancing supplement, are associated with a significantly shorter lifespan in men. The research, which analyzed data from over 20,000 participants across multiple cohorts, found that men with elevated glycine concentrations in their blood had a measurably higher risk of all-cause mortality. Women showed no such association.
Glycine is one of the most commonly purchased amino acid supplements on the market. It’s promoted for cognitive function, improved sleep quality, collagen production, and even anti-aging benefits. Estimates suggest millions of Americans take it daily, often stacking it alongside other nootropics in their morning routines. Greg, a 51-year-old software engineer in Austin, told me he’d been taking 3 grams of glycine every night for four years after reading about its sleep benefits on a longevity forum. “Nobody ever mentioned a downside,” he said. As We explored in a recent piece on supplement stacking gone wrong, the gap between what gets marketed online and what the evidence actually supports can be staggering.
The researchers, whose findings were covered by ScienceDaily, noted that glycine plays a dual role in the body. While it functions as a neurotransmitter and structural component of proteins, elevated blood concentrations appear to correlate with underlying metabolic dysfunction in men, including markers of liver stress and impaired mitochondrial function. The sex-specific nature of the finding surprised even the study authors. One hypothesis: differences in how men and women metabolize amino acids, influenced by hormonal profiles, may make men more vulnerable to glycine accumulation. As Medical Xpress reported, the researchers emphasized that glycine levels may serve as a biomarker for existing health problems rather than a direct cause of mortality, but the correlation was robust across all cohorts studied.
The finding adds another layer to an already complicated conversation about men’s longevity. As we wrote in a piece about social isolation and accelerated aging in men, the factors that shorten male lifespan are often the ones that get the least attention. Meanwhile, research into brain-protective proteins and dietary approaches to cognitive decline continues to point toward whole-system interventions rather than isolated supplement fixes.
The study’s authors were careful to note that they aren’t calling for a blanket ban on glycine supplementation. The amino acid occurs naturally in protein-rich foods and plays essential roles in the body. But the findings do raise serious questions about the wisdom of chronic, high-dose supplementation, particularly for men who may already have metabolic risk factors they aren’t aware of. For someone like Greg, the takeaway was immediate: he scheduled bloodwork with his doctor for the first time in two years. “I was so focused on optimizing,” he said, “that I forgot to check whether what I was doing was actually safe.”
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