Men's Testosterone Levels Determined by Where They Grow Up, Study Suggests

A man's testosterone levels are affected by where he grew up as a child, according to a study.

Clashing with the idea that testosterone is linked to genetics or race, U.K.-based researchers found a man's environment as a child can raise or lower his testosterone levels as an adult, triggering associated health problems.

Very high levels of testosterone can raise the risk of prostate diseases, and are linked to aggression as well as increased muscle mass. Very low levels of the hormone, however, can make men lethargic, affect their libido and cause erectile dysfunction.

Scientists at Durham University investigated the link between a boy's environment and his testosterone levels in adulthood by collecting data from 359 men. The men fell into one of five categories: 107 were born and raised in Bangladesh; 59 moved to the U.K. as children; and 75 arrived in the U.K. as adults. A further 56 were born in the U.K. to Bangladeshi parents, and 62 were ethnic Europeans born in the U.K.

Bangladesh and the U.K. were fruitful countries to compare because they have sharply contrasting levels of wealth. According to the latest figures published by the World Bank in 2017, almost three quarters of Bangladesh's population lived in poverty in 2016. In the U.K., that figure was 7.3 percent of the population according to official statistics released in 2017. (However, World Bank poverty criteria differs from that of the U.K. government's.)

Variables including their height, weight, age, as well as the age puberty began, were taken into account. Researchers also collected saliva from the participants.

The resulting data suggested Bangladeshi men who grew up and lived in the U.K. as adults had significantly higher levels of testosterone compared with relatively well-off men who were raised and lived in Bangladesh. However, the men's fertility was not affected by their testosterone levels, the researchers said.

What's more, the men of Bangladeshi origin in the U.K. also hit puberty at a younger age, and were taller than those who were raised in Bangladesh.

The results mirror findings by the researchers into how a girl's environment can affect their hormone levels, fertility rates and risks for cancers of the reproductive organs as adults.

The researchers behind the study published in the journal Nature Ecology and Evolution believe childhood ecology affects testosterone levels. For instance, if a child is faced with disease and poor nutrition, their body will prioritize survival over the production of testosterone.

Dr. Kesson Magid, of the department of anthropology at Durham University, told Newsweek: "While the clearest effects of environment were seen if men moved in their childhood before they turned nine years old, the data suggest that moving to an improved environment into teenage years may even lead to increased testosterone, growing taller and having an earlier puberty than men who never moved. This period of sensitivity to environment was later than I might have expected."

Dr. Gillian Bentley, a co-author of the study and professor of anthropology at Durham University, said in a statement: "Very high and very low testosterone levels can have implications for men's health and it could be important to know more about men's childhood circumstances to build a fuller picture of their risk factors for certain conditions or diseases."

This piece has been updated with comment from Dr. Kesson Magid.