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Developmental biology - Testosterone|
Testosterone is not strictly controlled by genetics
The study found that Bangladeshi men who grew up and lived as adults in the United Kingdom (UK) had significantly higher levels of testosterone compared to relatively well-off men who grew up and lived in Bangladesh as adults. Bangladeshis in Britain also reached puberty at a younger age and were taller than men who lived in Bangladesh throughout their childhood.
Researchers believe these differences are linked to energy investment. It may only be possible to have high testosterone levels if there are not many other demands placed on the body such as fighting off infection. In environments where people are more exposed to disease and/or poor nutrition, the body directs energy towards survival at the cost of reprouction.
The researchers collected data on height, weight, age at puberty and other health information including testosterone levels, from saliva samples of 359 men. They compared the following groups: (1) men born and still resident in Bangladesh; (2) Bangladeshi men who moved to the UK (London) as children; (3) Bangladeshi men who moved to the UK as adults; (4) second-generation, UK-born men whose parents were Bangladeshi migrants; and (5) UK-born ethnic Europeans.
"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."
Men with higher levels of testosterone are at greater risk of potentially adverse effects of this hormone on health and ageing. Very high levels can mean increased muscle mass, increased risk of prostate diseases and have been linked to higher aggression. Very low testosterone levels in men can include lack of energy, loss of libido and erectile dysfunction. The testosterone levels of the men in the study were, however, all in a range that would unlikely have an impact on their fertility.
"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," adds co-author Professor Gillian Bentley from the University of Durham.
Aspects of male reproductive function remain changeable in adolescence up to the age of 19, but are more flexible in early rather than late childhood, according to this research. However, the study suggests that in adulthood men's testosterone levels are no longer heavily influenced by their surroundings.
Girl's hormone levels, fertility and risk levels for reproductive cancers also increase based on the environment in which they grew up. This conclusion is based on previous research conducted by Gillian Bentley PhD, from the Department of Anthropology at the University of Durham, UK and co-author of the current study.
Male reproductive investment is energetically costly, and measures of human reproductive steroid hormones (testosterone), developmental tempo (pubertal timing) and growth (stature) correlate with local ecologies at the population level. It is unclear whether male reproductive investment in later life is ‘set’ during childhood development, mediated through adulthood, or varies by ethnicity. Applying a life-course model to Bangladeshi migrants to the United Kingdom, here we investigate plasticity in human male reproductive function resulting from childhood developmental conditions. We hypothesized that childhood ecology shapes adult trade-offs between reproductive investment and/or other fitness-related traits. We predicted correspondence between these traits and developmental timing of exposure to ecological constraints (Bangladesh) or conditions of surplus (United Kingdom). We compared: Bangladesh sedentees (n = 107); Bangladeshi men who migrated in childhood to the United Kingdom (n = 59); migrants who arrived in adulthood (n = 75); second-generation UK-born and raised children of Bangladeshi migrants (n = 56); and UK-born ethnic Europeans (n = 62). Migration before puberty predicted higher testosterone and an earlier recalled pubertal age compared with Bangladeshi sedentees or adult migrants, with more pronounced differences in men who arrived before the age of eight. Second-generation Bangladeshis were taller, with higher testosterone than sedentees and adult migrants, and higher waking testosterone than Europeans. Age-related testosterone profiles varied by group, declining in UK migrants, increasing in sedentees, and having no significant relationship within UK-born groups. We conclude that male reproductive function apparently remains plastic late into childhood, is independent of Bengali or European ethnicity, and shapes physiological trade-offs later in life.
Authors: Kesson Magid, Robert T. Chatterton, Farid Uddin Ahamed and Gillian R. Bentley .
The research was funded by the Economic and Social Research Council (ESRC), the Royal Society and Prostate Cancer UK, and involved researchers from the University of Chittagong (Bangladesh), Durham University (UK), and Northwestern University (USA).
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Men who grew up in England as children reached puberty younger, were taller and more fertile
than men who grew up in Bangladesh suffering disease and/or malnutrition as children.
Images: public domain.