Men’s average testosterone levels have halved in last 50 years, say scientists
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- Prof Hagai Levine presented a meta-analysis at the European Society of Human Reproduction and Embryology meeting in London showing total testosterone in men fell 54% between 1972 and 2019, based on six longitudinal studies covering 118,593 individuals across Israel, the US, Brazil, Finland, and Denmark.
- Each of the six studies individually found a decline, and the combined data showed the drop accelerated after 2000; the studies controlled for age but did not control for obesity, which is known to be strongly correlated with low testosterone.
- Levine, of the Hebrew University-Hadassah Braun School of Public Health, estimated one quarter to one half of the decline could be explained by obesity and metabolic syndrome, and called environmental factors including endocrine-disrupting chemicals and global heating likely contributors.
- Prof Channa Jayasena of Imperial College London countered that obesity and diabetes could account for "all of this" decline, and said researchers need to clarify whether environmental factors are independently driving the trend beyond those metabolic causes.
- Prof Allan Pacey of the University of Manchester warned that the social-media promotion of testosterone supplements is a growing concern because giving a man testosterone "switches off" his sperm production.
- US Health Secretary Robert F Kennedy Jr recently described male fertility decline as an "existential problem," lending political weight to the debate.
- The same research team previously concluded sperm counts have steeply declined over the past 40 years, earlier work that has fueled the broader public debate on male reproductive health.
Why it matters: The 54% decline across 118,593 men in five countries is the strongest evidence yet for what researchers call a "major crisis" in male reproductive health — but because obesity could potentially explain all of it, the role of environmental chemicals remains contested. Clinically, Pacey's warning that testosterone supplements suppress sperm production challenges the booming social-media pitch of "low T" treatments with no clear regulatory response in sight.
