Decreased estradiol levels and free androgen index and elevated sex hormone-binding globulin levels in male idiopathic osteoporosis

Estrogen deficiency is an important pathogenetic factor in female osteoporosis, and androgens are known to have anabolic effects on bone. In this study we have compared 12 men with idiopathic osteoporosis, age 27-55 years, with 12 age-matched men, with respect to serum levels of sex steroids, biochemical markers of bone turnover, bone density, and body composition. All subjects showed values within the normal range for all hormonal parameters. The patient group compared with the controls had significantly lower serum levels of estradiol (71 +/- 13 versus 85 +/- 14 pmol/liter, P < 0.03); estradiol/sex hormone-binding globulin (SHBG) ratio (22.4 +/- 12.1 versus 39.5 +/- 18.6 pmol/mg, P < 0.02); free androgen index (51.0 +/- 19.4 versus 74.1 +/- 33.1%, P < 0.05); and higher SHBG (3.7 +/- 1.6 versus 2.5 +/- 1.0 mg/liter; P < 0.04). The men with idiopathic osteoporosis had significantly lower body mass index (23.2 +/- 2.8 versus 25.9 +/- 3.3 kg/m(2), P < 0.05); and a tendency to lower percentage of total body fat (14.2 +/- 5.5 versus 18.6 +/- 6.0%; P < 0.10) than the controls. Regression analyses revealed that bone mineral density in femoral neck correlated significantly and positively with the ratio estradiol/SHBG (r = 0.67; P < 0.01) and negatively with SHBG concentrations (r = -0.63; P < 0.04) in the group of patients. These findings could represent a pathogenetic mechanism in male idiopathic osteoporosis.