Association between 25(OH)-vitamin D and testosterone levels: Evidence from men with chronic spinal cord injury

Objective: As an independent linear association between 25-hydroxyvitamin D (25(OH) D) and testosterone levels is controversial, this study aimed to explore this topic in men with chronic spinal cord injury (SCI), who exhibit a high prevalence of both androgen and vitamin D deficiency. Design: Forty-nine men with chronic SCI consecutively admitted to a rehabilitation program underwent clinical/biochemical evaluations. Results: Deficiency of 25(OH) D (<20 ng/mL) was found in 36 patients (73.5%). They exhibited significantly lower total testosterone and free testosterone levels, higher parathyroid hormone (PTH) and HOMA-IR, a poorer functional independence degree, and were engaged in poorer weekly leisure time physical activity (LTPA). Significant correlates of 25(OH) D levels were: total testosterone, free testosterone, PTH, functional independence degree and weekly LTPA. At the linear regression models, lower 25(OH) D levels were associated with both lower total and free testosterone after adjustment for age, smoking, alcohol consumption, comorbidities and HOMA-IR. However, after full adjustment, also including functional independence degree, BMI and LTPA, only the association of lower 25(OH) D with lower free testosterone was still significant. Conclusion: In men with SCI, 25(OH) D correlates with total and free testosterone and exhibits an independent linear association with free testosterone. Regardless of this independent link, hypovitaminosis D and androgen deficiency are markers of poor health, sharing common risk factors to take into account in the rehabilitative approach to patients with SCI.