Low body size and elevated sex-hormone binding globulin distinguish men with idiopathic vertebral fracture.

Factors predisposing to vertebral fracture in men are less well defined compared with women. Most studies of osteoporosis in men have included patients with low bone mineral density (BMD), with or without vertebral fracture, or have included other fractures. To clarify these associations we investigated sex hormone levels, bone markers, and (indirectly) lean body mass (LBM) in 81 men with idiopathic vertebral fracture. Serum testosterone, estradiol, sex-hormone binding globulin (SHBG), 24-hr urinary creatinine (24-hr UCr), urinary free deoxypyridinoline (UfDPD) and serum type I procollagen carboxy-terminal propeptide, type I procollagen amino-terminal propeptide, type I collagen carboxy-terminal telopeptide, and osteocalcin were measured. SHBG was higher and 24-hr UCr lower in osteoporotic subjects. UfDPD was higher when corrected for 24-hr UCr. Serum bone turnover markers were not significantly increased, nor were serum sex hormones (and free hormone indices) significantly decreased in patients. SHBG levels were inversely related with lumbar spine and femoral neck BMD in both patients and control subjects. Free estradiol index was only correlated with BMD in men with osteoporosis. Body size is lower in men with established osteoporosis. The normal free hormone indices suggest that SHBG does not affect free hormone levels whereas the relationship between SHBG (but not sex hormones) and 24-hr UCr points to a relationship between SHBG and LBM. The association of high levels of SHBG with low levels of LBM may indicate an action via the known inverse relationship of SHBG with IGF-I, though any action through IGF-I probably occurred at an earlier age than that at which the patients presented. Estrogen has no relationship with BMD in normal men but may play a role in men with osteoporosis.