Sex hormones and age: a cross-sectional study of testosterone and estradiol and their bioavailable fractions in community-dwelling men.

The role of endogenous sex hormones in many diseases makes understanding factors that influence levels of these hormones increasingly important. This study examined age-associated variations in total and bioavailable testosterone and estradiol levels among community-dwelling Caucasian men in Rancho Bernardo, California. Plasma samples obtained from 810 men aged 24-90 years in 1984-1987 were analyzed in 1993 using radioimmunoassay. Analyses of age-hormone associations, adjusting for weight, body mass index, alcohol ingestion, smoking, physical activity, caffeine intake, specimen storage time, and disease status, were undertaken. Bioavailable testosterone and bioavailable estradiol levels decreased significantly with age independently of covariates. Total testosterone and estradiol levels decreased with age only when analyses were controlled for confounders. The importance of the age-associated decline in endogenous sex hormone levels, particularly levels of bioavailable testosterone and bioavailable estradiol, and their relation to disease and function in men deserve further research.