Frequency of Vitamin D Deficiency and Associated Factors in Long-term Bariatric Surgery Patients: a Cross-sectional Study

Background Vitamin D deficiency is a common consequence of bariatric surgery (BS). However, few studies have evaluated influential factors and to date there are no studies investigating individual ultraviolet B (UVB) radiation levels in BS patients. This study aimed to evaluate vitamin D deficiency and its associated factors, including UVB radiation, in Roux-Y gastric bypass (RYGB) patients. Methods This study included 104 adults (90.4% female) at least 5 years after RYGB. Patients underwent surgery in private hospitals (Private; n = 47) or in two public hospitals, one with ongoing outpatient care (Active; n = 17), and the other with discontinued service for BS (Discontinued; n = 40). 25-hydroxyvitamin D (25(OH)D) concentrations were analyzed by chemiluminescence, individual UVB radiation levels by dosimeter badges. Vitamin D intake, anthropometric, skin phototype, sociodemographic and lifestyle patterns were also assessed. Results Mean age was 49.6 +/- 9.1 years and post-operative period 8.7 +/- 2.2 years. The prevalence of 25(OH)D deficiency and insufficiency was 25.0% and 51.9% respectively. 25(OH)D concentration differed among the hospitals (private = 26.2 +/- 8.5; active = 28.7 +/- 11.4; discontinued = 23.5 +/- 6.5 ng/mL; p = 0.038). A total of 26.2% of the variance observed in 25(OH)D concentrations was explained by daily UVB radiation levels (beta = 0.224; p = 0.032) and vitamin D intake (beta = 0.431; p < 0.001), controlling for age and BMI. Conclusion A quarter of the evaluated patients presented vitamin D deficiency, which was associated with the discontinuation of the health care, higher BMI, lower vitamin D intake, and lower individual UVB radiation levels.