Genetic and environmental influence on the association between testosterone, sex hormone-binding globulin and body composition in Korean men.

OBJECTIVES

This study aimed to evaluate an association between testosterone, sex hormone-binding globulin and body composition as well as the influence of genetic and environmental factors on the association.

DESIGN

A cross-sectional study.

SETTING

Community-based study.

PARTICIPANTS

One thousand and eighty-three Korean men including 144 pairs of monozygotic twins.

MAIN OUTCOME MEASURE: Levels of serum total testosterone (TT) and sex hormone-binding globulin (SHBG) were measured by chemiluminescence immunoassay, and free testosterone (cFT) was calculated using Vermeulen's method. Detailed body composition was measured using dual-energy X-ray absorptiometry. We performed linear mixed regression analysis with consideration of familial correlations and covariates.

RESULTS

Each 1-SD increase in age-adjusted levels of TT, cFT and SHBG was associated with lower levels of adiposity measures and absolute measures of lean body mass. On the other hand, percentage total lean mass increased with increasing levels of TT, cFT and SHBG (P < 0·05). Bivariate variance-component analyses revealed that most body composition measures had a significant inverse unique environmental correlation with both TT and SHBG, and a significant genetic correlation with TT. A co-twin control study in monozygotic twins showed that within-pair differences in adiposity measures were inversely associated with within-pair differences in the levels of TT and SHBG, while within-pair differences in lean mass were inversely associated with within-pair differences in the levels of TT.

CONCLUSIONS

The significant associations of body composition with testosterone and SHBG were influenced by both genetic and environmental factors. Further efforts to elucidate related genes and modifiable environmental factors are needed.