Salivary testosterone is associated with higher lumbar bone mass in premenopausal healthy women with normal levels of serum testosterone

The relationships among lumbar and femoral bone mineral density (BMD) and different forms of testosterone -total, salivary testosterone and free testosterone index (FTI) calculated with the sex hormone binding globulin (SHBG)-, body mass index (BMI) and body fat distribution (waist-to-hip ratio and breast-to-hip ratio) were analysed in a cross-sectional study with 66 Spanish premenopausal healthy women aged 42 years and with normal levels of serum testosterone. BMD was measured using dual-energy X-ray absorptiometry (Hologic QDR 1000(R)), and salivary and blood samples were obtained during early follicular phase. In a multiple stepwise regression analysis, lumbar BMD was positively predicted by salivary testosterone and negatively by SHBG adjusted by BMI (R-2 = 0.20; p < 0.02). The most femoral BMDs were negatively predicted by SHBG and positively by breast-to-hip ratio (R-2 = 0.22-0.33, according to the site measured), but neck BMD was not predicted by any variable. When FTI was entered into the regression model instead of SHBG, it was not an independent predictor of BMD. The waist-to-hip ratio was positively correlated with several femoral BMD sites, but breast-to-hip ratio was better predictor. After adjusting by SHBG, the BMI was only predictor for intertrochanter BMD. All women with elevated salivary testosterone (n = 12) had higher lumbar BMD than those with normal value (1.120 +/- 0.112 vs. 1.026 +/- 0.118; p < 0.01) without differences in other confounding variables. As a conclusion, in premenopausal healthy women of the same age with normal levels of serum testosterone, low levels of SHBG and high levels of salivary testosterone are associated with higher lumbar BMD, whereas low levels of SHBG together with higher breast-to-hip ratio are associated with higher femoral BMD.