Vitamin D Status and Seasonal Variation: A Retrospective Single Institution Database Study of Patients Pursuing Metabolic/Bariatric Surgery

Background Obesity is associated with suboptimal levels in vitamin D, a nutrient important for bone health and immune function. Seasonal variation in vitamin D may exacerbate this deficiency in persons with obesity, as exposure to ultraviolet B rays in sunlight is necessary for the conversion of vitamin D to its active form in the body. The aim of this study was to determine the relationship between season and vitamin D levels in persons with obesity pursuing bariatric surgery. Materials and Methods This retrospective cohort study from a single academic medical center investigated adult patients undergoing either primary sleeve gastrectomy (SG) or Roux-en-Y gastric bypass (RYGB) over a 20-year period. Demographics and serum 25-hydroxyvitamin D3 levels were collected from the first presenting visit to the bariatrics center. Continuous vitamin D3 levels were compared across seasons using a one-way Analysis of Variance (ANOVA). Vitamin D3 categories were examined across seasons using a Chi square test of independence. Results 1,256 persons pursuing bariatric surgery (SG: N=697, RYGB: N=559) met the inclusion criteria. Baseline vitamin D values were available in 1,071 of the eligible patients. Overall, serum 25-hydroxyvitamin D3 levels showed a significant variation across the seasons of the year (P<0.001), with highest levels during summer (33.52±12.70 ng/mL) and lowest levels during spring (29.72±12.34 ng/mL) and winter (29.90±14.80 ng/mL). Conclusions This study demonstrates marked seasonal variation in serum 25-hydroxyvitamin D3 in patients with obesity presenting for bariatric surgery. These results emphasize the importance of utilizing tailored supplementation during the spring and winter months to prevent potential deficiency.