Vitamin D Levels as an Important Predictor for Type 2 Diabetes Mellitus and Weight Regain Post-Sleeve Gastrectomy

Abstract

Weight Loss Surgery (WLS), including sleeve-gastrectomy (SG), results in significant weight loss and improved metabolic health in severe obesity (BMI ≥ 35 kg/m2). Previous studies suggest post-operative health benefits are impacted by nutrient deficiencies, such as Vitamin D (25(OH)D) deficiency, while it is currently unknown whether nutrient levels may actually predict post-surgery outcomes. As such, this study investigated whether 25(OH)D levels could predict metabolic improvements in patients who underwent SG. Patients with severe obesity (n = 309; 75% female) undergoing SG participated in this ethics-approved, non-randomized retrospective cohort study. Anthropometry, clinical data, 25(OH)D levels and serum markers were collected at baseline, 6-, 12- and 18-months post-surgery. SG surgery resulted in significant improvements in metabolic health at 6- and 12-months post-surgery compared with baseline, as expected. Patients with higher baseline 25(OH)D had significantly lower HbA1c levels post-surgery (p < 0.01) and better post-surgical T2DM outcomes, including reduced weight regain (p < 0.05). Further analysis revealed that baseline 25(OH)D could predict HbA1c levels, weight regain and T2DM remission one-year post-surgery, accounting for 7.5% of HbA1c divergence (p < 0.01). These data highlight that higher circulating 25(OH)D levels are associated with significant metabolic health improvements post-surgery, notably, that such baseline levels are able to predict those who attain T2DM remission. This highlights the importance of 25(OH)D as a predictive biomarker of post-surgery benefits.

Keywords: bariatric; diabetes; diabetes remission; obesity; sleeve gastrectomy; type 2 diabetes; vitamin D; weight regain.

Figure 1

Effect of sleeve gastrectomy surgery on fasting plasma glucose and HbA1c levels. (A) Fasting plasma glucose levels (F. Glucose) at baseline, 6- and 12-months post-surgery for non-T2DM and T2DM groups. (B) Serum HbA1c levels at baseline and 12-months post-surgery for non-T2DM and T2DM groups. Data are presented as mean ± standard error of the mean. Statistical differences between time points were determined via a 2-tailed paired t-test: ** p < 0.01, *** p < 0.001.

Figure 2

Changes in anti-diabetic medication intake post-surgery. (A) Boxplot displaying the distribution of Metformin intake at baseline and one-year post-surgery among patients with T2DM. (B) Percentage distribution of patients with T2DM at baseline who increased or did not change their dose of Metformin and those who stopped or reduced their dose of Metformin. Statistical differences between dose at baseline and dose at one year were obtained via 2-tailed paired t-test whereas statistical differences between subgroups of qualitative variables were obtained using chi-squared and McNemar tests: *** p < 0.001.

Figure 3

Summary of circulating 25(OH)D improvements. (A) Percentage distribution of T2DM and non-T2DM participants with deficient (<25 nmol/L), insufficient (25–50 nmol/L) and sufficient (>50 nmol/L) circulating 25(OH)D levels at baseline, 6-months and 12-months post-surgery for T2DM and non-T2DM groups. (B) Mean circulating 25(OH)D values at baseline, 6-months and 12-months post-surgery for T2DM and non-T2DM groups. Statistical differences between non-T2DM and T2DM cohorts were analyzed using 2-tailed independent samples t-test. * p < 0.05.

Figure 4

Association of 25(OH)D levels with weight regain and pre/post-surgical HbA1c. Scatter plot showing the correlation between (A) baseline 25(OH)D levels and baseline HbA1c for total cohort (n = 223), (B) baseline 25(OH)D levels and HbA1c levels at one-year post-surgery for total cohort (n = 209) (C) baseline 25(OH)D levels and baseline HbA1c depending on T2DM status (n = 105 for T2DM and n = 118 for non-T2DM)) and (D) baseline 25(OH)D levels and HbA1c levels at one-year post-surgery depending on T2DM status (n = 98 for T2DM and n = 111 for non-T2DM)). Linear trend line is shown with Pearson correlation statistic (r) and significance (p). p is considered significant if <0.05. Data were log-transformed prior to correlation analysis to improve normality.

Figure 5

Baseline 25(OH)D Predicts T2DM Remission One-Year Post-Surgery. (A) Expected and observed numbers of participants who either increased/did not change their anti-diabetic medication dose or decreased/stopped their medication at 12 months post-surgery, according to their baseline 25(OH)D status. (B) Bar chart showing mean baseline circulating 25(OH)D values for patients who increased/did not change their anti-diabetic medication dose (↑ dose) (n = 20), or decreased/stopped their medication (↓ dose) (n = 74) at one-year post-surgery. Data are displayed as mean ± standard error of the mean. Statistical mean differences were determined by 2-tailed independent samples t-test (Mann-Whitney U). ** p < 0.01. (C) Bar chart showing mean circulating 25(OH)D values at baseline, 6 months and one-year post-surgery for patients who were in remission (n = 60) and patients who remained diabetic (n = 48). Data are displayed as mean ± standard error of the mean. Statistical differences between the groups were analyzed using 2-tailed independent samples t-test. *** p < 0.001.