Objective: This study prompted us to investigate the relationship between 25-(OH) D (3) and the IGF-I system, leptin, sex, age, anthropometric and body composition variables in healthy adults. We hypothesised that these variables would regulate 25-(OH) D (3) concentrations.
Design: We included 253 subjects--126 men and 127 women. Body mass index (BMI) and body composition was determined, along with serum leptin, total IGF-I, free IGF-I, IGFBP3 and plasma 25-(OH) D (3) concentrations.
Results: 25-(OH) D (3) deficiency was observed in 69 subjects. There was a difference between 25-(OH) D (3) values and season (summer vs. winter). We observed similar 25-(OH) D (3) concentrations in men to those in women. The differential characteristics in subjects without 25-(OH) D (3) deficiency were lower BMI, fat mass and body fat and higher free IGF-I. We observed that leptin increased in the last decades and IGF-I system decreased by decade in both men and women. In subjects without 25-(OH) D (3) deficiency, there was a correlation between free IGF-I and 25-(OH) D (3) in men, and a negative correlation between 25-(OH) D (3) and age, BMI, fat mass and leptin and a positive correlation with total IGF-I in women. The multivariate linear regression analysis explained 37.8 % of 25-(OH) D (3) variability in men and 39 % in women, and only season and free IGF-I made an independent contribution to 25-(OH) D (3) in men, and season and fat mass in women.
Conclusion: These data suggest that free IGF-I in men and fat mass in women could regulate 25-(OH) D (3) concentrations.