Effects of vitamin D on insulin resistance in nursing home residents: an interventional study

Insulin resistance is defined as reduction of insulin-stimulated glucose uptake in skeletal muscles and inadequate suppression of the production of endogenous glucose. The aim of this study was to assess the effect of vitamin D intake on insulin resistance in aged patients.

This interventional study was carried out on residents of Sadeghieh Nursing Home in Iran. The participants were healthy adults aged ≥ 65. For eight weeks, the participants took pills containing 50,000 IU vitamin D(3) per week. Insulin resistance was defined as homeostasis model assessment of insulin resistance (HOMA-IR) > 2.5. We used McNemar's test, Wilcoxon test, chi-square, and Pearson correlation coefficient and SPSS software (v. 12) to analyse the collected data.

The average age of the 76 participants was 78.7 ± 8 years and 52 of the participants were female. Before and after the study, 37 and four participants had vitamin D deficiency, respectively (p < 0.001). Impaired fasting plasma glucose (FPG) and insulin resistance was not more prevalent in the participants with vitamin D deficiency. In this study, vitamin D intake had no significant effect on FPG level (p = 0.9), but it increased the prevalence of insulin resistance significantly (p < 0.001).

In our study, before and after the intervention, vitamin D deficiency had no relationship with FPG level and insulin resistance. Vitamin D intake had no significant effect on FPG level, but it increased the prevalence of insulin resistance significantly. We believe that performing more studies, with a longer timespan and larger sample size, as double-blind clinical trials, is necessary.