Men's average testosterone levels have dropped by 54% between 1972 and 2019, according to a meta-analysis presented at the European Society of Human Reproduction and Embryology annual meeting in London. Researchers warn this decline represents a major crisis in male reproductive health that is not receiving enough attention.
Study details and findings
The meta-analysis combined six longitudinal studies tracking testosterone levels in 118,593 individuals from Israel, the US, Brazil, Finland, and Denmark. Each study individually found a decline, and the combined data showed an overall drop of 54%, with the decline accelerating after 2000. This equates to more than a 1% decrease per year, a trend researchers describe as robust and not a statistical error.
Prof Hagai Levine of the Hebrew University-Hadassah Braun School of Public Health and Community Medicine stated: "We saw an over 50% decline in total testosterone over this time period. It reflects a more than 1% decline each year, so this is not a fluke, this is not a statistical error. It's very strong trend."
Possible causes: obesity, diabetes, and environmental factors
Rising levels of obesity and diabetes are expected to play a significant role. Excess body fat increases the conversion of testosterone into estrogen, lowering testosterone levels. Levine estimated that "maybe one quarter to one half of the decline would be explained by obesity and metabolic syndrome." However, the studies did not control for obesity, leaving room for other factors.
Environmental factors such as endocrine-disrupting chemicals found in household items and global heating may also contribute. Prof Channa Jayasena of Imperial College London called the findings "an important reality check" and said: "I do think male reproductive health is declining and appears to have been declining over time." He added that while obesity and diabetes could account for all of the decline, further research is needed to clarify the role of environmental factors.
Implications and debate
The findings add to a contentious debate about male fertility decline. Previous work by the same team concluded sperm counts have steeply declined over 40 years, with US health secretary Robert F Kennedy Jr describing it as an "existential problem." However, some scientists urge caution. Prof Allan Pacey of the University of Manchester noted a concern about the promotion of testosterone supplements on social media: "The solution that's being promoted is that we give you testosterone. But if you give a man testosterone, you switch off his sperm production. I've seen that in the clinic."
Levine emphasized the need for a precautionary approach: "The level of certainty that we need is not 95%. We should find better ways to prevent exposure of the general public to hazardous chemicals. And we don't do it well enough at the moment."
