A meta-analysis combining data from six longitudinal studies, spanning 1972 to 2019 and encompassing 118,593 individuals across five countries, indicates a 54% decline in average male testosterone levels. Researchers observed this trend, representing a decline of over 1% annually, and suggest it signals a potential male fertility crisis. The study, presented at the European Society of Human Reproduction and Embryology meeting, identified rising obesity and diabetes as likely contributors, with potential roles for environmental factors like endocrine-disrupting chemicals and global heating.

This finding adds weight to previous research on declining sperm counts and has sparked discussion within the scientific community. While some experts, like Prof Hagai Levine, emphasize the severity and urgency of the trend, others, such as Prof Channa Jayasena, caution that obesity and diabetes might fully account for the observed drop. The complex relationship between testosterone and overall health, affecting sperm production, libido, muscle mass, and mood, makes this decline a significant health indicator.

The research team controlled for age in their analysis, but acknowledged potential confounding factors like differing cohort average ages and the absence of obesity control. Levine estimates that obesity and metabolic syndrome could explain one-quarter to one-half of the decline. The study's authors advocate for the precautionary principle, urging better prevention of public exposure to hazardous chemicals due to inconsistent evidence on specific environmental factors. The increasing promotion of testosterone supplements, which can paradoxically suppress sperm production, also raises concerns among andrology experts.