Background: Hypovitaminosis D and low testosterone levels are common in men with T2DM, and vitamin D has been proposed to regulate pituitary-testicular function.

Objective: We investigated the association between testosterone levels and the circulating vitamin D among type 2 diabetic males.

Methods: We recruited 95 males with type 2 diabetes in this cross-sectional study and investigated the circulating form of vitamin D, which is 25-hydroxyvitamin D (25(OH) D). 25(OH) D level <30 ng/mL was used to define vitamin D insufficiency, and 25(OH) D level <20 ng/ml was defined as a deficiency. Testosterone deficiency was described as a total testosterone level less than 300 ng/dl.

Result: Testosterone deficiency prevalence in type 2 diabetic males was found to be 46.3%. Testosterone deficient people with diabetes had significantly lower 25(OH) D levels than patients with normal testosterone. We observed a higher prevalence of vitamin D deficiency in testosterone deficient people with diabetes than testosterone sufficient patients. Furthermore, significantly lower total testosterone levels but not LH levels were observed in diabetic males with vitamin D deficiency compared to nondeficient patients. We observed that 25(OH) D significantly predicted total testosterone levels in diabetic males evaluated by linear regression analysis. However, this association was no longer statistically significant after excluding macro-albuminuric patients. Moreover, vitamin D deficiency was found to be a significant risk factor for testosterone deficiency in logistic regression analysis.

Conclusion: Testosterone deficient males with diabetes had significantly lower 25(OH)D levels and a higher prevalence of vitamin D deficiency than normal testosterone diabetic males. Likewise, vitamin D deficient patients had lower testosterone levels. Overall, 25(OH) D significantly predicted total testosterone levels. Vitamin D deficiency was thus a significant risk factor for testosterone deficiency in diabetic males.