SCIENTISTS SAY MEN’S TESTOSTERONE FELL 54% SINCE 1972

Researchers told a fertility conference in London on Tuesday, July 7, 2026, that men’s testosterone levels fell an estimated 54% between 1972 and 2019, and they called it a major crisis in male reproductive health. They said rising obesity and diabetes probably explain part of the drop, though not necessarily all of it, and other experts urged caution about the conclusions.

The findings were presented at the annual meeting of the European Society of Human Reproduction and Embryology and first reported by The Guardian. The analysis pooled six earlier studies that tracked men over time, each with at least three time points. Together they covered 118,593 men from Israel, the US, Brazil, Finland and Denmark. Every one of the six found a decline on its own, and the combined drop appeared to speed up after 2000.

“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-Hadassah Braun School of Public Health and Community Medicine.

“We saw an over 50% decline in total testosterone over this time period,” Levine said. “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.”

Obesity, chemicals and a lot of caveats

The studies controlled for age individually, but differences in average ages between the groups of men may still have skewed the results. Obesity was not controlled for at all, even though it is strongly linked to low testosterone. Excess body fat can increase the conversion of testosterone into oestrogen.

Levine offered what he called an educated guess that obesity and metabolic syndrome might account for one quarter to one half of the decline. Prof Channa Jayasena of Imperial College London, a consultant in reproductive endocrinology, went further. “Obesity and diabetes could easily account for all of this,” he said, adding that researchers still need to check whether environmental factors are involved.

Jayasena nonetheless called the results “an important reality check.” “The fact that these studies have been done over several periods in history makes me actually convinced,” he said. He believes male reproductive health has been declining over time.

The team also pointed to endocrine-disrupting chemicals found in household items and to global heating as possible factors. Neither is an established cause, and studies on air pollution and endocrine-disrupting chemicals have produced inconsistent results. Levine said the precautionary principle should still apply. “The level of certainty that we need is not 95%,” he said.

Testosterone helps regulate sperm production and sex drive, builds muscle mass and bone density, and plays a role in mood, energy and metabolism.

Prof Allan Pacey, a professor of andrology at the University of Manchester who was not involved in the work, worried about where the low-testosterone narrative leads. He pointed to the growing promotion of testosterone supplements 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.”

The same research team’s earlier work on falling sperm counts was contentious among scientists. It also caught the attention of US health secretary Robert F. Kennedy Jr., who described male fertility decline as an “existential problem.”

The published abstract in Human Reproduction described the work a little differently. It reported a systematic review that screened 8,656 studies and included 12, covering 102,334 participants in seven countries. It found significant declines in total testosterone, free testosterone and sex hormone-binding globulin. Total testosterone fell by 0.26 nmol/L per year on average. The yearly drop was 0.17 nmol/L in studies sampled mostly before 2000 and 0.33 nmol/L in those sampled after.

The Jerusalem Post reported that the work formed part of Alon Levy’s master’s thesis in public health at the Hebrew University of Jerusalem. Yahoo Health noted that the 54% estimate does not mean a young man today has testosterone 54% lower than his grandfather at the same age, because the analysis spanned men of all ages.

On August 14, 2026, The Intercept reported that the 54% figure did not appear in the study materials it reviewed. It said the number might have been presented orally or in slides that were not public.