Adiposity is a confounding factor which largely explains the association of serum vitamin D concentrations with C-reactive protein, leptin and adiponectin

Objective: The role of adiposity in the relationship between vitamin D and inflammation is unknown. Our aim was therefore to assess the association of serum 25-hydroxyvitamin D (25(OH)D) with C-reactive protein (CRP), leptin and adiponectin and the role of adiposity in this relationship. Methods: This is a cross-sectional analysis of The Netherlands Epidemiology of Obesity Study (NEO), a population-based cohort study in men and women aged 45 to 65 years. Main outcome measures were CRP, leptin and adiponectin. In the linear regression analyses we adjusted for age, sex, ethnicity, creatinine, education, alcohol use, smoking status, physical activity, number of chronic diseases, season, total body fat and waist circumference. Results: Of the 6287 participants, 21% were vitamin D deficient (serum 25(OH)D < 50 nmol/L). Mean (SD) age and BMI were 56 (6) years and 26.3 (4.4) kg/m(2), respectively. Although after adjustment for most examined potential confounders, each 10 nmol/L increase in serum 25(OH)D was associated with 2.3% (95%CI: -4.0 to -0.5) lower CRP, 3.5% (-4.7 to -2.2) lower leptin, and 0.13 ng/mL (0.04-0.21) higher adiponectin, most of these associations seemed to largely stem from an additional potential confounder - adiposity - as they either disappeared (leptin and CRP) or were largely diminished (adiponectin) upon further adjustment for adiposity indices (total body fat and waist circumference). Conclusion: We found that measures of adiposity largely explained the negative association of serum 25(OH)D with the pro-inflammatory CRP and leptin, and the positive association with the anti-inflammatory adiponectin. These results suggest that future studies should take the effect of adiposity into account.