Major Decline in Male Testosterone Levels Over Five Decades
Men's average testosterone levels have fallen by more than half over the past 50 years, according to a new analysis presented at the annual meeting of the European Society of Human Reproduction and Embryology in London. The study, which examined data from over 100,000 men between 1972 and 2019, found a 54% decline in total testosterone levels, a trend researchers call a 'major crisis in male reproductive health.'
Data from Five Countries Points to Steep Decline
The meta-analysis combined six previous longitudinal studies tracking testosterone, each including at least three time points. Together, they covered 118,593 individuals from Israel, the United States, Brazil, Finland, and Denmark. Every individual study found a decline, and the combined data showed an overall drop of 54%, with the decline accelerating after 2000. 'We saw an over 50% decline in total testosterone over this time period,' said Prof Hagai Levine of the Hebrew University-Hadassah Braun School of Public Health and Community Medicine. '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 and Diabetes as Key Drivers
Rising levels of obesity and diabetes are expected to play a significant role. Testosterone regulates sperm production, sex drive, muscle mass, bone density, mood, energy levels, and metabolism. Excess body fat increases the conversion of testosterone into oestrogen, leading to lower testosterone levels. Prof Levine estimated that 'maybe one quarter to one half of the decline would be explained by obesity and metabolic syndrome.' However, other experts caution that obesity and diabetes could account for all of the decline. 'Obesity and diabetes could easily account for all of this,' said Prof Channa Jayasena of Imperial College London.
Environmental Factors Under Scrutiny
The research team suggests that environmental factors such as endocrine-disrupting chemicals found in household items and global heating could also contribute. Prof Levine stated, '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.' He called for applying the precautionary principle to protect the public from hazardous chemicals, despite uncertain evidence. '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.'
Debate Over Testosterone Supplements
The findings add to a widespread debate about male fertility decline. Previous work by the same team concluded that sperm counts have steeply declined over the past 40 years. However, the claims have been contentious. Prof Jayasena said the latest observations should act as 'an important reality check.' Prof Allan Pacey of the University of Manchester warned about the 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.'
Implications for Male Reproductive Health
Prof Levine emphasized that reproductive health is a signal of general health. 'I think that we have a major crisis in male reproductive health and it's currently not given enough attention,' he said. The study controlled for age, but confounding factors such as differences in average ages between cohorts may have influenced the results. Obesity was not controlled for, which is known to be strongly correlated with low testosterone. Researchers call for further investigation into environmental factors and improved prevention of exposure to hazardous chemicals.
