Scientists say average testosterone levels in men have halved over the past 50 years, and society is facing a male fertility crisis.
Total testosterone levels in men fell by 54% between 1972 and 2019, according to data presented at the European Society of Human Reproduction and Embryology’s annual meeting in London on Tuesday.
Rising levels of obesity and diabetes are expected to be a contributing factor, but the researchers suggest that endocrine-disrupting chemicals in various household products and environmental factors such as global warming may also be contributing factors to the apparent significant decline.
“I think there is a serious crisis in men’s reproductive health, and it’s not getting enough attention right now,” said Hagai Levin, a professor at Hadassah Brown School of Public Health and Community Medicine at the Hebrew University in Israel.
“We found that total testosterone decreased by more than 50% during this period,” he said. “This reflects a decline of more than 1% each year, so this is not a fluke or a statistical error. It is a very strong trend.”
The findings will be seen as an important contribution to the wider debate about whether and why male fertility is declining. Previous studies by the same research team that concluded that sperm counts have declined precipitously over the past 40 years have garnered public attention, with U.S. Secretary of Health Robert F. Kennedy Jr. recently describing declining male fertility as an “existential problem.”
However, this claim is controversial within the scientific community. Channa Jayasena, professor and consultant in reproductive endocrinology at Imperial College London, said the latest observations on testosterone should serve as an “important reality check”.
“It actually makes sense to me, given the fact that these studies have been done over several periods of history,” he says. “I think men’s reproductive health is declining, and it seems to be declining over time.”
The relationship between testosterone and health in men is bidirectional and complex. Testosterone regulates sperm production, sex drive, helps build muscle mass, bone density, and plays a role in mood, energy levels, and metabolism. Health factors such as obesity, where excess body fat increases the conversion of testosterone to estrogen, can lead to decreased testosterone. There is also significant medical controversy over the use of testosterone supplements, which can counterintuitively suppress sperm production.
“Reproductive health is a very important signal of general health,” Levine says. “We live in an environment that is not ideal for health in terms of climate and exposure to chemicals in terms of health behaviors.”
The meta-analysis combined six previous longitudinal studies tracking testosterone, with each study including at least three time points. These included data on 118,593 people from Israel, the United States, Brazil, Finland, and Denmark from 1972 to 2019.
Each study individually found a decline in testosterone, and when the data were combined the overall decline was estimated at 54%, and the decline appears to have accelerated since 2000.
Although the individual studies controlled for age, confounding factors such as differences in mean age between cohorts may have influenced the results. Obesity is also uncontrolled and is known to be strongly correlated with low testosterone.
“If I had to guess, and this is an educated guess, I would say that probably a quarter to a half of the decline would be explained by obesity and metabolic syndrome,” Levine said.
Some said such a conclusion would be premature. “Obesity and diabetes could very well be the cause of all this,” Jayasena says. “Testosterone levels clearly appear to be decreasing. What we need to do is find out whether environmental factors, in addition to obesity and diabetes, are causing this.”
Studies on air pollution and endocrine disruptors tend to yield inconsistent results, and it’s less clear what environmental factors are involved. Levine said the precautionary principle should be applied given the uncertain evidence.
“The level of certainty we need is not 95%,” he said. “We need to find better ways to prevent the public from being exposed to harmful chemicals, and we’re not doing enough right now.”
Professor Alan Pacey, professor of andrology at the University of Manchester, who was not involved in the study, said the concern about the theory that men have low testosterone was the increasing promotion of testosterone supplements on social media.
“The solution being promoted now is to administer testosterone,” he said. “But when you give men testosterone, it turns off sperm production. I’ve seen that in the clinic.”
