Does a high testosterone level have a positive impact on income and health? Scientists have long assumed this, especially in men. However, a new study shows that the causality is more likely to be the other way round: It is not a high testosterone level that makes successful, but success increases testosterone levels. This is the conclusion the researchers come to based on an analysis of the genetic, health and socio-economic data of over 300,000 people from the UK.
Numerous studies have linked testosterone in men to socioeconomic status and health. Accordingly, men with high testosterone levels are particularly willing to take risks and assertive, work more often as self-employed or in management positions, have a higher level of education, earn more money and are less likely to be overweight. “However, observational studies in adults, in which testosterone levels and the possible effects are measured together, say little about the causality,” says a research team around Sean Harrison from the University of Bristol in Great Britain.
Genetics as a basis
In order to find out whether testosterone actually influences success and health, or, conversely, whether the socio-economic circumstances have an effect on testosterone levels, the researchers chose a different approach: so-called Mendelian randomization. To do this, Harrison and his colleagues first identified genetic variants associated with higher testosterone levels and then examined how these variants were related to success and health. Since a person’s genetic code is already established before birth, these results cannot be distorted by later life events.
An association between the genetic predisposition to high testosterone levels and success in later life would therefore strongly suggest that testosterone does indeed have a causal influence. The basis for the survey was an extensive data set of 306,248 British men and women from the UK Biobank.
Overrated social impact
The result: If the researchers only looked at associations between adult testosterone levels and success, their results confirmed previous studies that found that men with more testosterone had higher household incomes, lived in better residential areas, and were more likely to have a college degree and a skilled job. In women, higher testosterone levels were associated with lower socioeconomic position. Also in line with previous findings, higher testosterone levels have been associated with better health in men, worse health in women, and higher risk-taking in men.
But a look at the genetic data showed that none of these associations were related to the genetic predisposition for high testosterone levels. “The effect sizes were smaller and the uncertainty intervals larger,” report the researchers. “There was little evidence of the effects of testosterone on any outcome.” Harrison’s colleague Amanda Hughes explains: “There is a widespread opinion that a person’s testosterone level can influence the future course of their lives. Our results suggest that, despite the many myths surrounding testosterone, its social impact may have been overstated. “
Wrong causality
Instead, from the researchers’ point of view, a reverse causality comes into question. “It is known that chronic stress can lower testosterone levels. Psychosocial stress due to socio-economic disadvantage could therefore influence testosterone levels as well as other health aspects, ”they explain. It is also conceivable that good health both increases testosterone levels and promotes professional success. Perception of one’s own success could also play a role: “In studies of sports competitions it was found that the testosterone level is higher in the winners than in the losers,” reports Hughes.
“In summary, our results suggest that many of the previously reported associations of testosterone with socioeconomic success, health, and risk taking are unlikely to be causal,” the researchers said.
Source: Sean Harrison (University of Bristol, UK) et al., Science Advances, doi: 10.1126 / sciadv.abf8257