The ESR1 gene is one of the genes used in combination to determine your testosterone levels. This gene controls the expression of an estrogen receptor important for sexual maturity, reproductive function as well as roles within tissues such as the bones. One of the alleles has been associated with lowering the levels of circulating testosterone.
Source: 1000 Genome Project. Global averages for both sexes
Sex hormones, like testosterone, are involved in the development of the sexual characteristics in men and women. In addition, they also help govern the processes that help tissues like muscle to grow, and nutrients to be stored and used. This means that how much testosterone you produce can alter the amount of muscle and fat in your body. The levels and activity of testosterone can vary from person to person due to both genetic and environmental factors. Understanding the relationship between all these factors enables us to advise how your genes and lifestyle may be affecting your testosterone profile.