Bioavailable testosterone (T) and estradiol (E2) as a function of age in a population cohort of men from Rochester, Minnesota. Error bars indicate standard error of the mean. Data from Dr. Khosla, et al. "Relationship of serum sex steroid levels and bone turnover markers with bone mineral density in men and women: A key role for bioavailable estrogen." The Journal of Clinical Endocrinology & Metabolism. 1998:83:7:2266-74.