Men’s Testosterone Levels Halved Over Five Decades, Researchers Reveal
Men’s average testosterone levels have declined by half in the last 50 years, according to scientists who warn that society is confronting a significant male fertility crisis.
Data presented at the annual meeting of the European Society of Human Reproduction and Embryology in London on Tuesday showed that total testosterone levels in men decreased by 54% between 1972 and 2019.
While rising obesity and diabetes rates are anticipated to contribute to this trend, the research team suggests that environmental factors such as endocrine-disrupting chemicals—found in various household products—and global warming may also play roles in this notable decline.
“I think that we have a major crisis in male reproductive health and it’s currently not given enough attention,” said Prof Hagai Levine, of the Hebrew University in Israel.
“We saw an over 50% decline in total testosterone over this time period,” he added. “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.”
The findings contribute significantly to the ongoing debate about whether male fertility is decreasing and the potential causes. Previous research by the same group, which indicated a decline in sperm counts over the past 40 years, has attracted public attention. US Health Secretary Robert F Kennedy Jr recently described the decline in male fertility as an “existential problem.”
However, these claims have been met with some skepticism. Prof Channa Jayasena, of Imperial College London and a consultant in reproductive endocrinology, stated that the latest testosterone observations should serve as “an important reality check.”
“The fact that these studies have been done over several periods in history makes me actually convinced,” he said. “I do think male reproductive health is declining and appears to have been declining over time.”
Complex Relationship Between Testosterone and Health
The relationship between male testosterone and health is multifaceted and bidirectional. Testosterone regulates sperm production, sex drive, muscle mass, bone density, and influences mood, energy levels, and metabolism. Certain factors, such as obesity—where excess body fat increases the conversion of testosterone into oestrogen—can result in lower testosterone levels. There is also ongoing medical debate regarding testosterone supplementation, which can paradoxically suppress sperm production.
“Reproductive health is a very important signal of general health,” said Levine. “We live in an environment that is not ideal for our health in terms of our exposure to chemicals in terms of climate and in terms of health behaviours.”
Meta-Analysis of Longitudinal Studies
The meta-analysis combined six previous longitudinal studies tracking testosterone levels, each including at least three time points. Collectively, these studies encompassed data from 118,593 individuals across Israel, the US, Brazil, Finland, and Denmark, spanning from 1972 to 2019.
Each individual study reported a decline in testosterone, and when combined, the overall decrease was estimated at 54%, with the decline appearing to accelerate after 2000.
The studies controlled for age, but potential confounding factors such as differences in average ages between cohorts may have influenced results. Obesity was not controlled for, despite its strong correlation with low testosterone.
“If I had to guess – and it’s an educated guess – I would say that maybe one quarter to one half of the decline would be explained by obesity and metabolic syndrome,” Levine said.
Others argue that such conclusions may be premature.
“Obesity and diabetes could easily account for all of this,” said Jayasena. “There appears to be a clear reduction in testosterone levels. What we need to do is to clarify, in addition to obesity and diabetes, whether environmental factors are provoking this.”
Uncertain Environmental Factors and Precautionary Measures
It remains unclear which environmental factors might contribute to the decline, as studies on air pollution and endocrine-disrupting chemicals have produced inconsistent results. Given the uncertain evidence, Levine advocates for applying the precautionary principle.
“The level of certainty that we need is not 95%,” he said. “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.”
Prof Allan Pacey, professor of andrology at the University of Manchester, who was not involved in the study, expressed concern about the narrative surrounding low testosterone on social media.
“The solution that’s being promoted is that we give you testosterone,” he said. “But if you give a man testosterone, you switch off his sperm production. I’ve seen that in the clinic.”
