Men’s testosterone levels in decline amid rising obesity, researchers warn

Men’s testosterone levels in decline amid rising obesity, researchers warn

Men’s testosterone levels in decline amid rising obesity, researchers warn

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Explainer: How genetics shapes obesity and why environment still matters

Charity Kilei

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16 hours agoRead nextOpens a fresh page.

According to the World Health Organisation (WHO), about one in six people globally experience infertility during their lifetime, with male factors contributing to nearly half of all infertility cases

Men’s reproductive health may be in decline, according to findings presented at the annual meeting of the European Society of Human Reproduction and Embryology.
Researchers analysed data from six long-term studies involving 118,593 men from Israel, the United States, Brazil, Finland and Denmark. They found that average total testosterone levels declined by 54 per cent between 1972 and 2019, far more sharply than expected.
“Over 50 per cent decline in total testosterone over this time period. It reflects a more than 1percent decline each year, so this is not a fluke, this is not a statistical error.”

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Testosterone is the primary male sex hormone and plays a vital role throughout a man’s life. Beyond regulating sperm production and sexual function, it helps maintain muscle mass, bone strength, red blood cell production, mood, energy levels and metabolic health.
While testosterone naturally declines with age, researchers say a consistent decline across entire populations suggests external factors may also be influencing hormone production.
Scientists believe rising obesity is one of the biggest contributors.

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Excess body fat increases the activity of an enzyme called aromatase, which converts testosterone into estrogen, reducing circulating testosterone. Obesity is also linked to chronic inflammation and metabolic dysfunction, both of which interfere with normal hormone production.
Diabetes may further worsen the problem. Insulin resistance and persistently elevated blood sugar levels can disrupt communication between the brain and the testes, reducing testosterone production over time.
However, the researchers acknowledged that their analysis did not adjust for obesity or metabolic disease, making it impossible to determine exactly how much of the decline is explained by these factors.
Environmental influences are also under investigation. Scientists have raised concerns about exposure to endocrine-disrupting chemicals found in plastics, pesticides, industrial compounds and personal care products.
These substances can interfere with hormone signalling, although evidence linking them directly to declining testosterone remains mixed. Air pollution, chronic stress, poor sleep, sedentary lifestyles and increasing exposure to heat have also been proposed as possible contributors.
Researchers caution that testosterone replacement therapy should not be viewed as a simple solution. While treatments are increasingly promoted for fatigue, low mood and age-related symptoms, medical experts warn that taking testosterone can suppress the body’s natural sperm production and, in some cases, reduce fertility.
As a result, men experiencing symptoms of low testosterone are encouraged to seek proper medical evaluation before considering hormone therapy.
In 2022, a landmark review published in Human Reproduction Update reported that sperm counts among men worldwide had fallen by more than 50 per cent between 1973 and 2018, with the rate of decline accelerating after 2000.
Researchers described the trend as a potential global public health concern because sperm count is considered an important indicator of men’s overall health and future disease risk.
Other studies have linked low testosterone to an increased risk of cardiovascular disease, type 2 diabetes, obesity, osteoporosis and depression.
Research published in Evolution, Medicine and Public Health also found that men with lower circulating testosterone may face a higher risk of premature death compared with men whose hormone levels remain within the normal range.
Although these studies do not prove that low testosterone directly causes these conditions, they suggest the hormone may serve as an important marker of overall health.

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