Low socio-economic status is a newly identified independent risk factor for poor vitamin D status in severely obese adults.

Background Hypovitaminosis D is very prevalent, especially in the obese population. However, the degree of severity and the parameters involved in vitamin D deficiency in this population are still unclear. The present study aimed to identify, from among the factors known to influence vitamin D status in a healthy population, those impacting the same parameter in obese population. Methods Serum 25- OH-D concentration was measured in 564 patients with class III obesity [i.e. severe and morbid obesity; mean (SD) body mass index ( BMI) 42.04 (6.92) kg m-2] and their demographic, clinical, biological, anthropometric, dietary and socio-economic data were collected. Results We observed that 96% of the obese patients had serum 25- OH-D lower than 30 ng mL−1. Severe vitamin D deficiency (serum 25- OH-D concentration <10 ng mL−1) affected 35% of this population. We found an inverse relationship between 25- OH-D levels and BMI ( P = 0.012), fat mass ( P = 0.041), metabolic syndrome ( P < 0.0001), fasting blood glucose ( P = 0.023), homeostasis model assessment for insulin resistance ( P = 0.008), waist circumference ( P = 0.001), and fasting blood triglycerides ( P = 0.002) and C-reactive protein ( P = 0.005). Low socio-economic status independently increased the risk of severe vitamin D deficiency [odds ratio ( OR) = 1.98; 95% confidence interval ( CI) 1.25-3.13], especially in the autumn-winter season ( OR = 2.94; 95% CI 1.98-4.36), morbid obesity ( OR = 3.19; 95% CI 1.49-6.82), metabolic syndrome ( OR = 1.6; 95% CI 1.06-2.42) and inflammation ( OR = 1.03; 95% CI 1.01-1.06). Conclusions Vitamin D deficiency is extremely common among obese patients, and the prevalence of severe deficiency is high. The association of adiposity, high body mass index, metabolic syndrome and inflammation with vitamin D status is marked, whereas low socio-economic status appears to be a major risk factor for severe vitamin D deficiency, suggesting that vitamin D deficiency may at least in part be responsible for the greater health vulnerability of populations with low socio-economic status. [ABSTRACT FROM AUTHOR]