Low testosterone levels in men at age 31 associates with future risk of prediabetes and type 2 diabetes: A birth cohort study.

Objective: We aimed to investigate the association of a low serum testosterone concentration with the risk of abnormal glucose metabolism (i.e., prediabetes and type 2 diabetes) in men at a 15-year follow-up.

Study population and methods: In a population birth cohort, men with low testosterone (testosterone < 12.1 nmol/L, n = 136) and normal testosterone concentration (testosterone ≥ 12.1 nmol/L, n = 2555) at age 31 were followed up until age 46. Blood samples were drawn at ages 31 and 46, and an oral glucose tolerance test (n = 1409) was performed at age 46.

Results: Men with low testosterone had significantly greater body mass index and waist circumference than men with normal testosterone at ages 31 and 46 (p < 0.001 in all comparisons). In men with low testosterone, the association with abnormal glucose metabolism was mainly driven by adiposity (p = 0.4 after adjusting for waist circumference). However, the risk remained increased, independently of waist circumference, when comparing the lowest and highest quartiles of testosterone (odds ratio:1.8 [95% confidence interval 1.3-2.7]) or when using testosterone as a continuous variable (odds ratio: 0.97 [95% confidence interval 0.95-0.99]). Between ages 31 and 46, body mass index increased more in men with normal testosterone at age 31 and low testosterone at age 46 than in men with normal testosterone or low testosterone at both ages (p < 0.001). Higher sex hormone binding globulin levels were associated with a lower risk for abnormal glucose metabolism independently of waist circumference (p < 0.001).

Conclusion: Low levels of testosterone and sex hormone binding globulin at age 31 associated with an increased risk of developing abnormal glucose metabolism after 15 years' follow-up. This association was partly independent of adiposity but was linked to waist circumference and weight gain.