Background Low vitamin D levels have been postulated to be associated with insulin resistance, suggesting that vitamin D plays a role in glucose metabolism and homeostasis.

Purpose To determine the prevalence of suboptimal vitamin D status in obese patients who are at risk of developing type 2 diabetes and its correlation with insulin resistance.

Material and methods Prospective observational study. We included obese patients (BMI >30 Kg/m²) assisted in endocrinology and nutrition, from October to December 2017. Demographic, clinical and biochemical data were evaluated. Vitamin D insufficiency was defined by 25OHD3 levels between 10–20 ng/ml and vitamin D deficiency was defined by levels of 25OHD3<10 ng/ml. Insulin resistance was estimated by fasting glucose and the HOMA-IR index >2.5. Statistical analyses were performed using the SPSS v.20 program. Associations between continuous variables were evaluated using a univariate linear regression test.

Results We evaluated 85 patients (27 men and 58 women). Mean age 43.8±14.5 years. BMI 43.6±8.2 Kg/m², systolic blood pressure (SBP) 133.4+-/18.7 mmHg, diastolic blood pressure (DBP) 84.6±11.1 mmHg, fasting glucose 100.8±30.6 mg/dl, glycated haemoglobin (HbA1C) 6.01+-/1.05%, total cholesterol (TC) 18.4±33.8 mg/dl, HDL cholesterol (HDL-c) 47.8±10.4 mg/dl, LDL cholesterol (LDL-c) 111.5±28.2 mg/dl, triglycerides (TG) 152.8±84.8 mg/dl and 25OHD3 17.5±6.01 ng/ml. 5.88% of participants had 25(OH)D concentrations<10 ng/ml. Serum levels of 25(OH)D showed a significant positive association with HOMA2-%S (p=0.01) and an inverse association with HOMA2-%B (p=0.07) and insulin levels (p=0.01), independent of other factors usually associated with insulin resistance such as age and BMI.

Conclusion Our results highlight the relationship between circulating 25(OH)D and glucose homeostasis in obese patient candidates for bariatric surgery. Consistent with our findings, a recent study has shown a significant increase in HOMA-IR, HbA1c and fasting plasma glucose in healthy individuals with serum concentrations of 25(OH)D<20 ng/mL versus those with 25(OH)D concentrations>40 ng/mL. We suggest that the optimisation of serum levels of 25(OH) D in obese patient candidates for bariatric surgery could represent a preventive strategy against the development of metabolic syndrome, type 2 diabetes and cardiovascular risk. Future prospective intervention studies with a larger sample size are needed to confirm this hypothesis.

Reference and/or acknowledgements Esteghamati A, Aryan Z, Esteghamati A, et al. Vitamin D deficiency is associated with insulin resistance in nondiabetics and reduced insulin production in type 2 diabetics. Horm Metab Res 2015;47:273–9.

No conflict of interest.