Hypovitaminosis D is Independently Associated with Metabolic Syndrome in Obese Patients

Background: Metabolic syndrome (MS) and hypovitaminosis D represent two of the most diffuse condition worldwide, reaching pandemic proportions in industrialized countries, and are both strongly associated with obesity. This study set out to evaluate the presence of an independent association between hypovitaminosis D and MS in an adult population of obese subjects with/without MS. Methods: We recruited 107 consecutive obese subjects, 61 with MS (age(mean +/- SD) 45.3 +/- 13.3 years, BMI(mean +/- SD): 43.1 +/- 8.3 kg/m(2)) and 46 without MS (age: 41.8 +/- 11.5, p = n.s., BMI: 41.6 +/- 6.5 kg/m(2), p = n.s.) comparable for sex, BMI, waist circumference and body fat mass, evaluated by bioimpedentiometry. 25(OH) vitamin D-3 levels were measured by colorimetric method. Insulin resistance was estimated by fasting blood insulin, HOMA-IR and ISI. Results: Serum 25(OH) D3 levels were significantly lower in MS obese patients than in obese subjects without MS (median(range) 13.5(3.3-32) vs 17.4(5.1-37.4), p<0.007). Low 25(OH)D-3 levels correlated with glycaemia (p<0.007), phosphate (p<0.03), PTH (p<0.003) and the MS (p<0.001). Multivariate model confirmed that low 25(OH)D-3 levels were associated with the diagnosis of MS in obese patients independently from gender, age, serum PTH and body fat mass. After stratifying the study population according to 25(OH)D-3 concentrations, patients in the lowest quartile showed a markedly increased prevalence of MS compared to those in the highest quartile (OR = 4.1, CI 1.2-13.7, p = 0.02). Conclusions: A powerful association exists between hypovitaminosis D and MS in obese patients independently from body fat mass and its clinical correlates. This indicates that the association between low 25(OH)D-3 levels and MS is not merely induced by vitamin D deposition in fat tissue and reinforces the hypothesis that hypovitaminosis D represent a crucial independent determinant of MS.