JAKARTA - The average testosterone levels of men in six long-term studies dropped by 54 percent from 1972 to 2019. A number of scientists assessed the findings showed serious problems in men's reproductive health, although the cause of the decline could not be determined.
The Guardian, quoted on Sunday, July 12, said the results were presented at the annual meeting of the European Society of Human Reproduction and Embryology in London on Tuesday.
The analysis combined data from 118,593 people from Israel, the United States, Brazil, Finland, and Denmark. Each study monitored testosterone levels at least three different periods.
When all the data is combined, total testosterone levels are estimated to have dropped 54 percent in 47 years. The decline has also been seen to be accelerating after 2000.
"We saw a decrease of more than 50 percent during that period," said Prof. Hagai Levine of the Hebrew University-Hadassah Braun School of Public Health and Community Medicine in Israel.
According to Levine, the figure is equivalent to a decrease of more than 1 percent every year.
"So, this is not a coincidence and not a statistical error. The trend is very strong," he said.
Testosterone plays a role in sperm production, sexual arousal, muscle formation, bone density, mood, energy, and metabolism.
However, the relationship between hormone levels and health is not simple. Obesity and diabetes are suspected to be important factors. Excess body fat can accelerate the conversion of testosterone to estrogen so that levels decrease.
Levine estimated that a quarter to a half of the decline may be related to obesity and metabolic disorders.
However, Prof Channa Jayasena from Imperial College London believes obesity and diabetes could explain the entire decline.
"It seems that there is a clear decrease in testosterone levels. What we need to make sure is whether environmental factors also contribute to it besides obesity and diabetes," he said.
The research team also suspected the influence of hormone-disrupting chemicals, air pollution, and global warming. Hormone-disrupting chemicals are substances that can disrupt the work of the hormone system in the body.
However, evidence regarding environmental factors has so far been inconsistent.
The analysis also has limitations. Obesity was not controlled in the pooled study, even though the condition is strongly associated with low testosterone. The mean age difference between groups may also affect the results, although each study has adjusted for age.
This finding adds to the debate over declining male reproductive health. The same team previously reported a sharp drop in sperm counts in the past 40 years.
Experts also warn of the dangers of using testosterone supplements indiscriminately. The product is increasingly being promoted through social media as a quick way to overcome low hormone levels.
Prof Allan Pacey from the University of Manchester said that giving testosterone from the outside can actually suppress sperm production.
"The solution that is promoted is to give you testosterone. However, if a man is given testosterone, his sperm production actually stops. I've seen it in the clinic," he said.
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