Men's average testosterone levels fell 54 percent since 1972, study finds

Men’s average testosterone levels have fallen by 54% since 1972, according to a study presented at the European Society of Human Reproduction and Embryology annual meeting in London, sparking warnings of a “major crisis in male reproductive health.” The research, led by Prof. Hagai Levine of the Hebrew University-Hadassah Braun School of Public Health and Community Medicine in Israel, analyzed data from six longitudinal studies tracking testosterone levels in 118,593 men across Israel, the U.S., Brazil, Finland, and Denmark between 1972 and 2019. The findings reveal a consistent decline of over 1% per year, with the rate of reduction accelerating after 2000.

The study attributes the drop to a combination of factors, including rising obesity and diabetes rates, which are known to lower testosterone by increasing estrogen conversion and impairing hormonal regulation. Environmental influences, such as endocrine-disrupting chemicals in household products and global warming, are also implicated, though their exact role remains debated. “We live in an environment that is not ideal for our health,” Levine said, emphasizing the need for stricter regulations on chemical exposure and lifestyle changes to mitigate the crisis.

The relationship between testosterone and health is complex. The hormone regulates sperm production, sex drive, muscle mass, bone density, and metabolism. Obesity, in particular, exacerbates the decline by converting testosterone into estrogen, while diabetes disrupts signals from the brain’s hypothalamus and pituitary gland, which govern hormone production. Despite these links, the study’s authors acknowledge that obesity and metabolic syndrome may account for only a portion of the decline, with environmental factors potentially playing a larger role.

Experts remain divided on the extent of environmental influence. Prof. Channa Jayasena of Imperial College London, a reproductive endocrinology consultant, noted that while obesity and diabetes could explain much of the trend, further research is needed to isolate environmental contributions. “There appears to be a clear reduction in testosterone levels,” he said, “but we must clarify whether factors like air pollution or endocrine-disrupting chemicals are also driving this.” Studies on these environmental agents have yielded inconsistent results, complicating efforts to pinpoint specific causes.

The findings add to a growing body of research on declining male fertility. Levine’s team previously documented steep drops in sperm counts over the past 40 years, a trend that has drawn attention from public figures like U.S. Health Secretary Robert F. Kennedy Jr., who called it an “existential problem.” However, the study’s methodology has faced scrutiny. Critics point out that the analysis did not control for obesity, a known confounder, and that differences in cohort ages might have influenced results. Levine estimated that obesity and metabolic syndrome could explain up to half the decline, but others argue that the evidence for environmental factors remains inconclusive.

Concerns also extend to the medical use of testosterone supplements. Prof. Allan Pacey of the University of Manchester warned that promoting testosterone replacement as a solution could worsen the crisis. “If you give a man testosterone, you switch off his sperm production,” he said, citing clinical observations. This paradox has fueled debates about the risks of over-the-counter supplements, which are increasingly marketed despite limited understanding of their long-term effects.

The study’s authors advocate for a precautionary approach, urging stricter regulation of chemicals and public health initiatives to address lifestyle factors. “The level of certainty that we need is not 95%,” Levine said. “We should find better ways to prevent exposure of the general public to hazardous chemicals.” As the debate continues, the research underscores the urgent need to understand and address the complex drivers of declining male hormonal health.