Hypovitaminosis D in bariatric surgery: A systematic review of observational studies

Abstract

Background: Obesity is a public health problem that carries global and substantial social and economic burden. Relative to non-surgical interventions, bariatric surgery has the most substantial and lasting impact on weight loss. However, it leads to a number of nutritional deficiencies requiring long term supplementation.

Objectives: The aims of this paper are to review 25-hydroxyvitamin D [25(OH)D] status pre and post bariatric surgery, describe the dose response of vitamin D supplementation, and assess the effect of the surgical procedure on 25(OH)D level following supplementation.

Methods: We searched Medline, PubMed, the Cochrane Library and EMBASE, for relevant observational studies published in English, from 2000 to April 2015. The identified references were reviewed, in duplicate and independently, by two reviewers.

Results: We identified 51 eligible observational studies assessing 25(OH)D status pre and/or post bariatric surgery. Mean pre-surgery 25(OH)D level was below 30ng/ml in 29 studies, and 17 of these studies showed mean 25(OH)D levels ≤20ng/ml. Mean 25(OH)D levels remained below 30ng/ml following bariatric surgery, despite various vitamin D replacement regimens, with only few exceptions. The increase in post-operative 25(OH)D levels tended to parallel increments in vitamin D supplementation dose but varied widely across studies. An increase in 25(OH)D level by 9-13ng/ml was achieved when vitamin D deficiency was corrected using vitamin D replacement doses of 1100-7100IU/day, in addition to the usual maintenance equivalent daily dose of 400-2000IU (total equivalent daily dose 1500-9100IU). There was no difference in mean 25(OH)D level following supplementation between malabsorptive/combination procedures and restrictive procedures.

Conclusion: Hypovitaminosisis D persists in obese patients undergoing bariatric surgery, despite various vitamin D supplementation regimens. Further research is needed to determine the optimal vitamin D dose to reach desirable 25(OH)D levels in this population, and to demonstrate whether this dose varies according to the surgical procedure.

Keywords: Bariatric surgery; Obesity; Predictor; Vitamin D deficiency; Vitamin D dose.

Figure 1. Flow diagram for study selection for the period 2000–2015

Following title and abstract and full text screening, 51 articles were included in the systematic review.

Figure 2. Mean 25(OH)D level (ng/ml), by BMI categories, before bariatric surgery in observational studies

Studies represented are those that have a number of participants of at least 50 per study sub-group. Surgical procedures include malabsorptive and combination procedures, except DiGiorgi 2008, Laparoscopic Adjustable Gastric Banding arm [58], Lanzarini 2014, Laparoscopic Sleeve Gastrectomy (LSG) arm [60], Capoccia 2012, LSG [76], Van Rutte 2014, LSG [62], Ben Porat 2015, LSG [65]. Red bars represent studies with mean BMI ≥ 50 kg/m²; Blue bars represent studies with mean BMI between 45 and 50 kg/m²; Green bars represent studies with mean BMI ≤ 45 kg/m². The difference between the weighted mean 25(OH)D levels in BMI categories was not clinically significant and did not show a decrease in 25(OH)D level with increasing BMI.

Figure 3. Mean 25(OH)D level before and 1 year after bariatric surgery in observational studies

Studies represented are those that have a number of participants of at least 50 per study subgroup. Surgical procedures include malabsorptive and combination procedures, except DiGiorgi 2008, Laparoscopic Adjustable Gastric Banding arm [58], and Capoccia 2012, Laparoscopic Sleeve Gastrectomy [76]. Studies were divided according to vitamin D supplementation dose range. All subjects were allocated vitamin D supplementation post operatively at various doses, as mentioned in the figure; for full details see Appendix. 25(OH)D status following supplementation showed a trend for a larger increase in 25 (OH)D level with higher vitamin D supplementation doses. The red color indicates a significant change in 25(OH)D level. The blue color indicates a non-significant change in 25(OH)D level. The black color indicates that statistical significance of the change in 25(OH)D status was not reported in the individual study. * Type of vitamin D not provided. **Excluding Fish et al