Development of a broader understanding of Vitamin D levels in patients undergoing sleeve gastrectomy to inform guidelines for post-surgery supplementation

None listed

Surgery provides the most efficient method of weight loss in severely obese patients, but also leads to malabsorption of micronutrients. Sleeve gastrectomy is a purely restrictive procedure and removes the greater curvature of the stomach leaving a small gastric sleeve. Advantages include rapid weight loss, comorbidity reduction, and avoidance of the complications seen in bypass procedures. Nutrient deficiency in this patient group is common, with Vitamin D deficiency reported in 21-80% of patients one year post-surgery. This may predispose these patients to poorer health outcomes, as inadequate Vitamin D levels have been associated with disruptions to calcium homeostasis, impaired bone metabolism and osteoporosis, cancer, insulin resistance, diabetes, cognitive dysfunction, depression and cardiovascular disease. However, there is also current debate around whether Vitamin D levels are a marker for, rather than a cause of chronic illness. It would be expected that stored Vitamin D in the extensive adipose tissue of these patients would help correct deficient levels as weight is lost, although there is no evidence to support this in the literature. It is possible that these patients have: (i) excess storage and potential dysfunctional metabolism and release of Vitamin D from adipose tissue; (ii) lower sun exposure and dietary intake due to lifestyle factors, or (iii) impaired synthesis and release from the skin. These mechanisms are unclear, and there are few published studies about treating Vitamin D deficiency post-surgery in this patient group and no consensus on recommendations for supplementation dosage and duration for gastric sleeve, or indeed any of the bariatric surgeries. This emphasises a significant gap in patient care recommendations. There is currently insufficient evidence to support the development of uniform supplementation guidelines post-surgery for patients undergoing bariatric surgery, and data for sleeve gastrectomy patients is most lacking, therefore protocols for supplementation are only consensus-driven. Further understanding the effect of supplementation in gastric sleeve patients is critical, as two recent studies have suggested Vitamin D supplementation may cause net harm in other groups and a recent systematic review confirmed little to no association between 25(OH)D levels and the course of a range of diseases/conditions shown to be associated with low 25(OH)D levels in epidemiological studies (e.g. cancer, insulin resistance, diabetes, cognitive dysfunction, cardiovascular disease). Current reasoning behind this null effect includes variations in baseline levels, body mass index and genetic variations in response to supplementation. There is significant individual variation in 25(OH)D levels pre-bariatric surgery, with most patients being deficient (<25nmol/L) or insufficient (<50nmol/L). There is also evidence for varied responses to set doses of Vitamin D3 post surgery however there is no data on this for patients undergoing sleeve gastrectomy. Genetic variation in the Vitamin D binding protein and the Vitamin D receptor in target tissues has been implicated in such variation in obese individuals. The current test for Vitamin D – serum 25(OH)D levels – does not account for this potential genetic variation, or for individual variation in Vitamin D metabolism (i.e. production of active metabolites) in tissues. Measuring the variation in genes for the Vitamin D binding protein and Vitamin D receptor alongside the response to Vitamin D supplementation would add clarity to the variations in responses to Vitamin D supplementation in order to determine evidence-based supplementation guidelines. The mechanistic work completed as part of this study will form the basis of future clinical trials to optimise supplementation strategies for these patients. In addition to the lack of understanding of the basis of 25(OH)D levels and supplementation response in sleeve gastrectomy patients, there is no evidence of the contribution of UV exposure and diet on Vitamin D status in these patients. As UV exposure plays an important part in endogenous production of Vitamin D, this is vital. In a group with already restricted intake and a higher risk of nutrient deficiencies, understanding the influences on Vitamin D intake and production are critical to optimising sun exposure, dietary intake and supplementation practices. Aims *To optimise patient outcomes post gastric sleeve surgery by achieving adequate and sustained 25(OH)D levels through individualised supplementation (usual care) *To establish the variation in 25(OH)D levels in patients undergoing gastric sleeve surgery before and 6, and 12-months after surgery to monitor the effect of usual care supplementation practices *To examine differences in 25(OH)D levels in patients before and 6 and 12-months after gastric sleeve surgery according to direct and indirect measures of sun exposure, detailed dietary intake data, genetic variation in the circulating Vitamin D binding protein and Vitamin D receptor, to provide pilot data on the variation of individualisation required in future supplementation practice

No related papers found yet.