The impact of age, body mass index and testosterone on erectile dysfunction.

Purpose: Erectile dysfunction (ED) may be associated with low serum total testosterone (T), low serum bioavailable testosterone (BAT) and high body mass index (BMI) in aging men.

Materials And Methods: A total of 675 workers (age range 45 to 60 years old) were entered into this study. Investigations were performed directly at their place of work. Exclusion criteria were abnormal urogenital status, antihypertensive drugs, medication possibly affecting the endocrine function and a history of previous pelvic trauma. T and sex hormone-binding globulin were measured with commercially available assays, and BAT was calculated from T and sex hormone-binding globulin. BMI was assessed and every individual completed a self-administrated questionnaire for erectile function (International Index of Erectile Function [IIEF-5]).

Results: T and BAT showed a significantly negative correlation with age and BMI. Each additional year of increase in age caused a decrease in the IIEF-5 score of 0.195 (p <0.001). Increase in BMI by 1 kg/m reduced IIEF-5 by 0.141, independent of age (p =0.005). Multiple logistic regression analyses confirmed the influence of increased age and higher BMI on the risk of ED. The corresponding odds ratio for ED was 1.082 (p <0.001) and 1.076 (p <0.001), respectively. These data indicate an increase in ED risk by 8.2% per year and by 7.6% per kg/m BMI. Severe cases of ED (IIEF-5 score 7 or less) were significantly associated with a decrease in T and BAT. Individuals with low BAT (1 ng/ml or less) had a 3 times higher risk of severe ED compared with men with BAT greater than 1 ng/ml (odds ratio 3.045, 95% CI 1.088 to 8.522, p =0.034). The result of the multiple logistic regression analysis was adjusted to age and BMI, and did not show a significant influence on the incidence of severe ED.

Conclusions: BMI contributes strongly to ED. Low T or BAT are only relevant if IIEF-5 questionnaire results in severe ED.