WESTPORT, CT (Reuters Health) – Estrogen levels are responsible for both the gain in bone mineral density (BMD) in young men and its loss in elderly men, according to investigators at the Mayo Clinic and Foundation in Rochester, Minnesota.
Dr. Sundeep Khosla and colleagues measured bone mineral density in 88 men ages 22 to 39 and for 130 men ages 60 to 90. Dual energy x-ray absorptiometry was performed on the subjects at baseline, 2 years, and 4 years. The researchers also measured circulating total and bioavailable estrogen and testosterone levels.
In young men, BMD increased significantly in the forearm and at the hip over the 4-year study period, the investigators report in The Journal of Clinical Endocrinology and Metabolism for August. BMD decreased in the forearm and remained stable at the hip in the elderly men.
In the young men, the rate of increase in BMD correlated with total and bioavailable estradiol and estrone levels, but not with testosterone levels. In the older men, the rates of bone loss correlated with bioavailable estradiol levels but, again, not with testosterone.
Dr. Khosla's group found that aging men whose serum bioavailable estradiol levels drop below about 11 pg/mL appear to be at the greatest risk for bone resorption.
The researchers note that the ability to aromatize testosterone to estradiol is enhanced with aging. This finding emphasizes "the importance of the decline in substrate and the increase in sex hormone binding globulin as the major reasons for the age-related decrease in bioavailable estradiol levels," the researchers write.