A meta-analysis of six long-term studies found that the average testosterone level in men decreased by more than 50% from 1972 to 2019. The findings were presented on Tuesday at the annual meeting of the European Society of Human Reproduction and Embryology in London.
Researchers suggest that this decline may be linked to rising obesity and diabetes rates, as well as environmental factors such as endocrine disruptors—chemical substances that can interfere with the hormonal system—and global warming. “I think we have a serious crisis in men’s reproductive health, and it is not being given enough attention at the moment,” said Professor Hagai Levine from the Hebrew University—Hadassah Braun School of Public Health and Community Medicine in Israel. “We have seen over a 50% decrease in total testosterone over this period. This reflects a decrease of more than 1% per year, so this is not a coincidence and not a statistical error. This is a very strong trend.”
Debates on male reproductive health
These results could significantly contribute to discussions about the potential decline in male reproductive health and its causes. A previous study by the same group of scientists, which reported a substantial decrease in sperm count over the past 40 years, garnered widespread attention. U.S. Health Secretary Robert F. Kennedy Jr. recently described the issue of male fertility as “existential,” although these assessments remain a topic of scientific debate.
Professor Channa Jayasena from Imperial College London, a consultant in reproductive endocrinology, described the new findings as a “significant reality check.” “The fact that these studies were conducted over several historical periods actually convinces me,” he said. “I really believe that men’s reproductive health is declining and seems to have been declining over time.”
Testosterone plays a crucial role in sperm production, sex drive, maintaining muscle mass, and bone density, and it also affects energy levels, mood, and metabolism. Health status can also influence testosterone levels; for instance, obesity can lead to the conversion of testosterone to estrogen, resulting in lower testosterone levels. Additionally, the medical community continues to debate the use of testosterone drugs, which can suppress sperm production.
“Reproductive health is a very important signal of overall health status,” Levine noted. “We live in an environment that is not ideal for our health in terms of chemical exposure, climate, and health behavior.”
Possible causes of testosterone decline
The meta-analysis combined six longitudinal studies, each including at least three time points of observation. In total, the studies covered data from 118,593 men from Israel, the USA, Brazil, Finland, and Denmark from 1972 to 2019. Each study observed a decrease in testosterone levels independently, and when combined, the overall decline was estimated at 54%. According to the authors, this trend may have accelerated after 2000.
The authors note that while individual studies accounted for the participants’ age, other factors may have influenced the results. In particular, obesity was not controlled for, despite its known association with decreased testosterone levels. “If I had to guess—and this is an educated guess—I would say that perhaps a quarter to half of the decline can be explained by obesity and metabolic syndrome,” Levine said.
At the same time, Professor Channa Jayasena cautioned against jumping to premature conclusions. “Obesity and diabetes could easily explain all of this,” he noted. “There seems to be a clear decrease in testosterone levels. We need to clarify, besides obesity and diabetes, whether environmental factors are provoking this.”
Scientists emphasize that there is still insufficient evidence to identify specific environmental causes, as studies on air pollution and endocrine disruptors have yielded conflicting results. Nevertheless, Levine believes the precautionary principle should be applied. “The level of confidence we need is not 95%,” he said. “We must find better ways to prevent the impact of dangerous chemicals on the general public. And we are not doing this well enough at the moment.”
Professor Allan Pacey, an expert in andrology at the University of Manchester who was not involved in the study, also warned against the uncontrolled use of testosterone drugs, which are becoming increasingly popular on social media. “The proposed solution is that we give you testosterone,” he said. “But if you give a man testosterone, you turn off sperm production. I have seen this in the clinic.”
Source: The Guardian
