Vitamin D, PTH, and the metabolic syndrome in severely obese subjects

The objective of this study was to evaluate the association between the metabolic syndrome (MS) and vitamin D [25(OH)D] or parathyroid hormone (PTH) levels in severely obese subjects.

Cross-sectional study in 298 severely obese patients [body mass index (BMI) 46.7 +/- 5.3 kg/m2; women/men, 70.4/29.6%; age 42.9 +/- 10.6 years]. Logistic and stepwise regression models were fit to estimate the odds for the MS (revised ATPIII criteria) and each of its individual components across quartiles of 25(OH)D and PTH after adjusting for age (years), gender, BMI, %FM, and season of blood sample collection.

Insufficient 25(OH)D and elevated PTH plasma levels were encountered, respectively, in 64.3 and 47.4% of the studied subjects. The prevalence of MS was 79.5%. In the unadjusted analysis, those in the highest quartile of 25(OH)D were less likely to present the MS [0.42 (95% CI 0.19-0.96)], hyperglycemia [0.47, (0.24-0.92)], high triglycerides [0.48 (0.25-0.95)], low HDL-cholesterol [1.51 (0.76-2.98)], and high blood pressure [0.35 (0.16-0.77)]. Nonetheless, these odds ratios lost significance after adjustment for age, gender, BMI, fat mass, and season. Backward stepwise regression analysis showed that only male gender [2.66 (1.16-6.10)] and age [1.07 (1.03-1.10)] were predictive variables for the MS. We did not find an association between the PTH quartiles and the MS or its individual components.

Our data are consistent with previous reports on the high prevalence of alterations in calcium metabolism in severely obese subjects. However, our data do not support an independent contribution of 25(OH)D or PTH in the pathogenesis of the MS in severely obese subjects.