The average levels of the hormone testosterone may have fallen by more than 50 per cent among men in the last five decades, according to an alarming new study warning about an ongoing male fertility crisis.
Testosterone is widely known, not just for its role in sperm production and libido regulation, but also for helping manage mood, energy levels, overall metabolism, as well as muscle mass and bone density.
In new research, scientists conducted a review of six long-term studies that tracked changes in testosterone among men.
Overall, the analysis included data on testosterone levels in nearly 118,600 men between 1972 and 2019 from five countries, including Israel, the US, Brazil, Finland and Denmark.
The findings confirm men’s average testosterone levels in 2019 had decreased by more than 50 per cent compared with 1972, say researchers led by Hagai Levine at the Braun School of Public Health of the Hebrew University-Hadassah in Israel.
There were confirmed signs of declining testosterone levels in every individual study included in the analysis.
Taken together, the average reduction rate since 1979 was 54 per cent, and the pace of decline seems to have accelerated particularly after 2000, scientists say.
This is roughly a one per cent drop each year, indicating that the fall in testosterone levels is a strong trend, and not due to chance or statistical error, they warn.
Obesity and diabetes could be the major causes behind the decline in male hormone levels, scientists say.
As body fat levels rise due to obesity, testosterone gets converted into the female hormone estrogen, lowering testosterone levels.
Insulin resistance in diabetic patients and chronic high blood sugar can impair the function of the brain’s hypothalamus and pituitary glands.
This can, in turn, reduce the brain signals that tell the body to produce testosterone, researchers say.
Environmental factors like hormone-disrupting substances found in household products such as forever chemicals may also be contributing to the testosterone level decline, scientists suspect.
The yet-to-be peer-reviewed study, titled “Temporal trends in total and free testosterone (1972-2019): a systematic review and meta-trend analysis”, was presented at the European Society of Human Reproduction and Embryology (ESHRE) 2026 in London on Tuesday.
It adds to a previous finding by the same team that sperm counts have declined sharply over the past 40 years.
However, experts caution that testosterone supplements may not be a one-size-fits-all solution to the problem, as they can signal the brain that the body has sufficient quantities of the male hormone and suppress its natural production.