Testosterone, body fat, controlled by same genes

Washington, Aug 6 : Genes that regulate a portion of body fat are also behind controlling levels of testosterone in men, according to the latest research.

It showed a 23 percent overlap between the genes that control testosterone and body fat composition, suggesting that these two variables are partly controlled by the same set of genes.

The study led by Jean-Marc Kaufman at Ghent University Hospital, Belgium was carried out on healthy male sibling pairs and estimated the extent to which sex hormones and body fat are controlled by the same genes.

The research involved 674 men from 274 independent families, as part of a larger study investigating the origins of body composition, sex steroid status and peak bone mass in healthy men.

Each participant had their weight, total body fat and BMI measured and a blood sample was taken to measure their levels of testosterone and SHBG (a protein that binds to sex hormones).

The team then used two computer programmes (SAGE and SOLAR 2.0) to carry out complex statistical modelling to calculate the 'heritability estimate' of each trait, that is, the extent to which each characteristic is influenced by genes (as opposed to environmental factors).

The correlation between two different variables, testosterone and body fat, was then calculated, based on their individual heritability estimates.

A strong correlation was found between sex hormones and body fat, which was predominantly due to shared genes. Specifically, testosterone and SHBG both showed a 23 percent genetic correlation with body fat, and SHBG showed a 29 percent link with whole body fat.

When measured individually, testosterone had the highest heritability estimate of the sex hormones at 0.65 (heritability estimates are measured on a scale between 0 and 1, with 1 equalling 100 percent genetic influence).

SHBG, weight and body fat also had high heritability estimates of 0.73, 0.83 and 0.65, respectively. Such high heritability values are similar to those previously published, and indicate that circulating testosterone levels are approximately 60 percent influenced by genes.

Previous studies have shown a well-established relationship between testosterone and body fat composition. For example, men with low testosterone levels are characterised by a high body fat percentage.

These findings have been published recently in Clinical Endocrinology.