Routine post-op supplementation can reduce vitamin D deficiency

Patients who adhered to a programme of routine post-surgical supplementation can reduce Vitamin D deficiency and insufficiency, according to researchers from the University of Manchester, Manchester Metropolitan University, Manchester and Salford Royal NHS Foundation and University Teaching Trust, Salford, UK.

In the study, ‘Vitamin D Status After Gastric Bypass or Sleeve Gastrectomy over 4 Years of Follow-up’, published in Obesity Surgery, the authors note that there is little known about the of prevalence of vitamin D insufficiency/deficiency in bariatric surgical patients in North West England and if the recommended vitamin D supplementation is adequate after surgery. As a result, they conducted a longitudinal, four-year cohort analysis of vitamin D and associated outcomes of 460 patients who underwent gastric bypass (n=292, 63.5%) or sleeve gastrectomy (n=168, 36.5%). All patients completed a minimum 12 months post-operatively and the number of patients who completed 24, 36 and 48 months post-operatively was 362, 253 and 149, respectively. They collected standard baseline demographics, as well as blood tests including total vitamin D (25-hydroxyvitamin D, 25(OH)D), phosphate, alkaline phosphatase (ALP), parathyroid hormone (PTH), albumin and total calcium.

Outcomes

Of the 460 patients, the majority were female (n=299, 65%), the mean age at time of surgery was 48.0 (+10.5) years and the baseline weight was 144.7 (+27.3) kg and BMI 50.0 (+7.6). At four years, weight loss was sustained with a non-significant (ns) rise in BMI from 35.1 (6.6) at 12 months to 37.2 (7.2) at 48 months. Regarding the procedures, the %TWL for gastric bypass vs. sleeve gastrectomy was 32.6% vs. 29.4% (p<0.001) at 12 months, 35.5% vs. 29.1% (p<0.001) at 24 months, 33.5% vs. 27.0% (p<0.006) at 36 months and 30.8% vs. 25.8% (ns) at 48 months. The authors reported that there were no consistent significant differences in weight loss between men and women or people with or without diabetes. In addition, post-operative reductions in HbA1c were similar with no significant difference between surgical or sex groups.

The outcomes showed that that routine post-surgical supplementation can reduce vitamin D deficiency - the pre-operatively mean vitamin D level was 33.1 (23.9) nmol/L; post-operatively, the vitamin D level increased to 57.4 (27.4) nmol/L at four months (p<0.001) and was maintained at subsequent timepoints. There was no significant difference in vitamin D levels between the procedures throughout the period of study. Parathyroid hormone levels overall or by type of surgery did not change significantly and calcium levels reduced significantly by 12 months post-surgery and beyond compared to baseline.

The researchers noted at baseline, there was a significant inverse correlation between BMI and vitamin D level (p<0.001) and this weakened with significant weight loss at 12 months (p<0.02) and thereafter. There was also a significant positive correlation between %TWL and vitamin D level demonstrating the greater the excess weight loss the higher the vitamin D level. There was a significant positive correlation between %TWL and vitamin D at four months (p<0.034), 12 months (p<0.049) and 24 months (p<0.019) but not thereafter. Finally, they reported that there was not a significant correlation between %TWL and change in vitamin D level from baseline at any time during the study.

The authors acknowledged that the study outcomes are limited by the retrospective nature of the cohort analysis and that a major limitation was patients being lost to follow-up.

“We report that vitamin D deficiency was prevalent in bariatric surgical candidates pre-operatively and routine vitamin D supplementation can reduce rates of post-operative vitamin D deficiency in patients undergoing weight loss surgery,” the authors conclude. “However, some patients remain poorly optimised despite this. Further research could investigate risk factors for difficult-to-optimise vitamin D status as well as different supplementation methods and dose regimens.”