Endocrine Abstracts

Backgrounds: One of the most observations in subjects with obesity, is a high prevalence of vitamin D deficiency, which, in turn, it has been implicated with decreased testosterone levels and an increased hypogonadism risk. Testosterone deficiency is a very common feature in males with obesity. However, only few studies have investigated the effect of vitamin D on testosterone in the context of obesity, and controversial results has been found.

Hypothesis: We hypothesized that a low serum 25-hydroxyvitamin D (25(OH)D) levels may be associated with a decreased testosterone levels in males with obesity. In addition, we also hypothesized that 25(OH)D levels may differ notably according to the different grade of obesity, as a result/consequence of variations in the body mass index (BMI).

Objectives: The aim of the present study was to investigate the relationship between serum 25(OH)D and testosterone levels in young Spanish men with different grade of obesity.

Methods: The study cohort consisted of 269 healthy young men with obesity Men (BMI ≥ 30 kg/m²) aged between 18 and 49 years old, and recruited in Málaga (Spain), between June 2013 to June 2015. Participants were divided under the 50^th percentile of serum 25(OH)D levels (134 subjects with vitamin D sufficiency and 135 with vitamin D deficiency). We have measured serum 25(OH)D and sex-related hormones. The associations between 25(OH)D and reproductive hormones and hypogonadism were analyzed using linear regression and binary logistic regression analyses, respectively.

Results: The 25(OH)D deficiency group had significantly decreased both serum total and free testosterone levels and increased serum androstenedione levels when compared to the 25(OH)D sufficiency group (P<0.05). Using multivariable lineal regression analyses, 25(OH)D was correlated with the majority of sex-related hormones. However, this significant association disappeared when we adjusted this model by BMI. Further, we analyzed the effect that BMI exerted on the association between 25(OH)D and testosterone, analyzing different grade of obesity. We found that subjects with obesity type III, and adjusted by age, smoking status and BMI, showed that both total testosterone and SHBG were significantly and positively associated with 25(OH)D. Using a mediation analysis, we observed a partial effect of BMI on the association between 25(OH)D and total testosterone levels, indicating that 25(OH)D influence total testosterone levels, and BMI partially mediated this association.

Conclusions: Serum 25(OH)D is associated with total testosterone levels in those subjects with morbid obesity.