The effect of changes in adiposity on testosterone levels in older men: longitudinal results from the Massachusetts Male Aging Study

Abstract

Objective: Changes in adiposity affecting total testosterone (TT) and free testosterone (FT) levels have not been examined in a population-based survey. We aimed to determine whether changes in adiposity predict follow-up levels and rates of change in TT, FT and sex hormone-binding globulin (SHBG) in men. Design: The Massachusetts Male Aging Study is a randomly sampled, population-based cohort interviewed at baseline (T1, 1987–1989; n = 1709; aged 40–70 years) and followed-up approximately 9 years later (T2, 1995–1997; n = 1156). Men were categorized as overweight (body mass index (BMI) ≥ 25 kg/m2) or having obesity (BMI ≥ 30 kg/m2), waist obesity (waist circumference ≥ 102 cm), or waist-to-hip ratio (WHR) obesity (WHR>0.95). For each adiposity group, we constructed four categories to represent changes between T1 and T2: overweight (or obese, etc.) at neither wave, T1 only, T2 only, or both waves. Results: After adjustment for confounding variables, men who were overweight at T2 only, or at both waves, had significantly lower mean T2 TT and SHBG levels than men in the neither group (P<0.05). Mean FT did not differ between any overweight group and the neither group. Men who were obese at both times, had the highest mean BMI, the highest fraction of severely obese men, and significantly greater rate of decline in FT than the neither group. Conclusions: In men who become overweight, the greater rate of decline in TT, but not FT, is related mostly to a lesser age-related increase in SHBG. Since weight gain is highly prevalent in older men, over-reliance on TT levels in the diagnosis of androgen deficiency could result in substantial misclassification.