Free and bioavailable fractions of sex steroids may influence bones in young men, depending on age and oestradiol level.

INTRODUCTION: Longitudinal bone growth ceases by the end of puberty, and it is thought to be a result, in both sexes, of increased pubertal oestrogen serum concentrations. Since peak bone mass is achieved by the third decade of life or later, the aim of this study was to relate sex steroid hormones and sex hormone binding globulin (SHBG) levels to bone quality in men during their third and fourth decades of life. MATERIAL AND METHODS: Eighty men, healthy volunteers aged between 18 and 39 years, were subjected to an interviewer-administered questionnaire, body mass index (BMI) measurement, blood sample and calcaneal quantitative ultrasound (QUS) (Hologic-SAHARA). Blood was assessed for testosterone (T), oestradiol (E2), dehydroepiandrosterone sulfate (DHEAS), SHBG, luteinising hormone (LH) and follicle stimulating hormone (FSH). Free and bioavailable T and E2 levels were calculated knowing SHBG and albumin levels. RESULTS: While T, E2, DHEAS, LH and FSH levels were not related, free and bioavailable fractions of T and E2 were positively associated with QUS readings. SHBG level was associated negatively. After dichotomisation for age, the associations remained significant only for younger subjects (18-30 years, n = 47). After adjustment for other co-variants, only SHBG in younger subjects retained its negative association with QUS. Older subjects (31-39 years, n = 33) revealed higher BMI and lower serum concentrations of total (-17 %), free (-18.5%) and bioavailable (-22.5%) levels of E2 than younger subjects. CONCLUSION: Free and bioavailable fractions of sex steroids may influence bones in young men, depending on age and E2 level.