A new study led by Durham University has revealed that men’s testosterone levels in adulthood are shaped by their childhood environment, refuting previous theories that production of the sex hormone is chiefly mediated by genetics.

The research was initiated after a handful of recent investigations found that women who grew up with fewer resources and higher exposure to pathogens – essentially, third-world conditions – have lower levels of sexual hormones, reduced ovulation, and undergo menopause sooner than women who spent their childhood in more affluent regions. Investigations on individuals born in Bangladesh, a poor nation beset with economic and health disparities from which many people migrate, further suggests that developmental outcomes are different between those who remain in poverty throughout childhood and adolescence vs those who migrate to richer areas.

Yet until now, no work had assessed whether this pattern holds true for men as well.

To explore the impact of life history on male reproductive traits, lead author Dr Kesson Magid compared health information of 297 young to middle-aged Bangladeshi men: 107 residents, 59 migrants who arrived in the UK during childhood, 75 migrants who arrived in adulthood, and 56 UK-born children of immigrants. Sixty-two UK-born ethnic Europeans were also included. The analysis is published in the journal Nature Ecology & Evolution.

As Dr Magid and his co-authors predicted, men who moved to the UK as children had higher levels of testosterone, went through puberty sooner, and were taller than men who remained in Bangladesh, implying that the migrants’ bodies were able to direct more energy toward reproductive and physiological development because the energy demands for basic survival were exceeded. They note that the differences were most extreme in those who moved before age nine – prior to the onset of puberty. Second-generation British-Bangladeshi men also had higher testosterone levels and were taller than non-migrants, yet those who resettled as adults remained comparable.

“The above findings lend further support to the ‘developmental hypothesis’, whereby pre-birth, early infancy or childhood conditions influence reproductive development in later infancy, developmental transitions to adulthood, and adult reproductive and [physiological] traits in both women and men,” the authors conclude.  

Dr Magid, commenting in a statement, added that a “man’s absolute levels of testosterone are unlikely to relate to their ethnicity or where they live as adults but instead reflect their surroundings when they were children.” 

According to co-author Gillian Bentley, insights into the factors controlling testosterone are quite valuable for medical scientists, as both over- and underproduction of the hormone are associated with increased risk of disease and various unpleasant conditions, such as low libido and decreased fertility (low testosterone) and aggression and prostate cancer (high levels).