Positive effect of vitamin D supplementation on weight loss in obese patients treated with glucagon-like peptide 1 and lifestyle interventions

Abstract

Background. Obesity, prediabetes and type 2 diabetes mellitus (T2DM) are global diseases affecting the population of Ukraine, with an annual increase in morbidity. Insulin resistance occurs in up to 90 % of obese patients, contributing to the accumulation of white adipose tissue, and has a risk for the further development of prediabetes and T2DM. However, other factors also play a negative role in the development of obesity, particularly cholecalciferol (vitamin D) deficiency. Vitamin D is a steroid hormone the main function of which is to regulate calcium and phosphorus metabolism, but this molecule also exhibits va­rious properties, including the effects on carbohydrate metabolism. The purpose of this study was to identify and evaluate the role of vitamin D elevation in patients receiving glucagon-like peptide-1 agonists (GLP-1a) in combination with lifestyle interventions for the treatment of obesity and to compare its effectiveness with that in patients treating with metformin and sodium-glucose cotransporter 2 inhibitors (SGLT2i). Materials and methods. A prospective study included 155 obese patients, and follow-up data were available for 49 of them. The study group consisted of 30 patients receiving combination therapy with GLP-1a liraglutide at a dose of 1.2 to 3.0 mg per day. The control group included 19 patients recei­ving combination therapy with metformin in daily doses of 500 to 2,000 mg, and SGLT2i in daily doses of 10 to 12.5 mg. Treatment of vitamin D deficiency was performed with cholecalciferol at a dose of 4,000 IU/day. Results. In study group GLP-1a, 25 (83.3 %) patients had vitamin D insufficiency, which is statistically similar to control group (p > 0.05) — 17 (89.5 %) cases. All patients with vitamin D insufficiency received 4,000 IU of cholecalciferol daily during the follow-up period. In study group GLP-1a, the mean body mass before the treatment was 104.6 kg, after treatment — 96.36 kg (p = 0.000007), the mean weight lost was 7.8 % (range is 1–23.71 %) of the initial level. Mean body mass index (BMI) before treatment was 37.1 kg/m2, after treatment — 34.11 kg/m2 (p = 0.000006). In the control group, the mean weight before the treatment was 99.4 kg, after treatment — 91.74 kg (p = 0.000196), the mean weight lost was 7.73 % (range is 0–16.9 %) of the initial level. BMI before treatment averaged 35.6 kg/m2, after treatment — 34.11 kg/m2 (p = 0.000196). The analysis of carbohydrate metabolism parameters showed a significantly lower blood glucose level — 5.75 mmol/l in the study group GLP-1a compared to 8.42 mmol/l in the control group (p = 0.00024). It should be noted that a similar clinical picture was also observed after treatment, despite the compensation of T2DM in all patients: a significantly lower blood glucose level — 5.03 mmol/l in the study group GLP-1a compared to 5.99 mmol/l in controls (p = 0.002453). However, significantly higher levels of insulin were detected in the study group GLP-1a before treatment — 27.02 mU/L compared to 18.59 mU/L in control patients (p = 0.003286). After treatment, a similar situation was observed in terms of significantly higher levels of insulin: 19.41 mU/l in patients of the study group GLP-1a compared to 14.42 mU/l in controls (p = 0.0024). Corresponding changes were also observed for the HOMA index. Conclusions. Our results suggest high effectiveness of increasing the level of vitamin D in case of its insufficiency as a part of measures for the treatment of obese patients with liraglutide, metformin or SGLT2i.