Childhood environment, rather than genetics or ethnicity, is the major factor influencing men's testosterone levels, according to a new study.
A study of 359 men, published in Nature Ecology and Evolution, suggests that men who grow up with high exposure infectious diseases are more likely to have lower levels of testosterone, a key hormone involved in muscle mass and male fertility, later in life.
'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,' said study author Professor Gillian Bentley from the University of Durham.
The researchers compared testosterone levels among men of Bangladeshi and European heritage who had grown up either in Bangladesh or the UK, in an attempt to parse out the effects of genetic background and environment. They measured the hormone levels in Bangladeshi men born, raised and still living in Bangladesh; Bangladeshi men born in Bangladesh who moved to the UK as children; second-generation men of Bangladeshi heritage born and raised in the UK as second-generation migrants; and UK-born men of European heritage.
Bangladeshi men who had grown up in the UK had significantly higher levels of testosterone than
those who remained in Bangladesh, the study found.
The study collected data on height, weight, age at onset of puberty, as well as measuring testosterone levels in saliva samples. The researchers found that Bangladeshi men who had moved to the UK as children reached puberty at a younger age and were taller than men who lived in Bangladesh throughout childhood. The research also suggests that in adulthood men's testosterone levels are no longer as heavily influenced by their surroundings as they are during childhood.
The researchers suggest that the lower testosterone levels were likely to be due to growing up in an environment with more infectious diseases. In these conditions, the body diverts more resources to fighting infection and coping with poorer nutrition rather than producing testosterone, according to the study.
High levels of testosterone are linked to increased muscle mass, increased risk of prostate conditions and higher aggression. Conversely, very low testosterone levels are associated with lack of energy, loss of libido and erectile dysfunction. The new findings have important implications for screening as researchers suggest that a man's childhood environment should also be taken into account. However, all men in this study had testosterone levels within a normal healthy range.