Osteoporosis in men: A potential role for the sex hormone binding globulin

The exact mechanism of bone loss remains unknown in primary male osteoporos is. It has been suggested that estrogen and sex hormone binding globulin (S HBG) play a role in regulating bone turnover and bone mass in healthy men > 65 years of age. In the present study, 80 men (mean age 49.7 years) with b one mineral density >2.5 SD below the young adult value and 40 age-matched controls were recruited to evaluate the relationships between sex hormone l evels, bone biochemical markers levels, and bone mineral density. Fasting s erum samples were assayed for total and free testosterone total estradiol, and SHBG. The free androgen index, was calculated as: [total testosterone/S HBG * 100]. Bone remodeling was evaluated by measurement of urinary levels of the C-telopeptide of type I collagen (CTx) and free deoxypyridinoline (D -Pyr), serum osteocalcin, and bone-specific alkaline phosphatase (bSAP). Th ere was no significant difference between controls and osteoporotic men acc ording to age, body mass index (BMI), total testosterone, and estradiol. In contrast, serum SHBG level was significantly higher (+42.2%), whereas free androgen index was lower (-24.8%) in patients with primary or secondary os teoporosis. Testosterone and estradiol levels did not correlate with any bo ne resorption or bone formation markers. In contrast, stepwise linear regre ssion analysis showed that SHBG was significantly correlated with D-Pyr (r = 0.45, p < 0.05) and CTx (r = 0.34, p < 0.05) in primary osteoporosis. In secondary osteoporosis, SHBG was correlated with D-Pyr (r = 0.48,p < 0.05) and bSAP (r = 0.55,p < 0.01). After adjustment for age and BMI, hip bone mi neral density (BMD) was not associated with testosterone or estradiol but o nly with serum SHBG (r = -0.33, p < 0.01) in primary osteoporosis. The same relationship was observed in men with secondary osteoporosis (r = -0.34,p < 0.01). Among osteoporotic patients, spinal radiography showed at least on e vertebral crush fracture in 36 men and none in 44. Serum SHBG concentrati on was significantly associated with the presence of vertebral fracture: th e odds ratio was 2.0 (95% confidence interval [CI] 1.2-3.5) for an increase of one standard deviation of SHBG. In conclusion, the present study showed that serum SHBG concentration is increased in middle-aged men with primary or secondary osteoporosis and is correlated with bone remodeling markers, hip bone mineral density, and vertebral fracture risk. (C) 2001 by Elsevier Science Inc. All rights reserved.