Controversial Impact of Vitamin D Supplementation on Reducing Insulin Resistance and Prevention of Type 2 Diabetes in Patients with Prediabetes: A Systematic Review

Abstract

Background: Prediabetes has become a worldwide health problem. Multiple clinical trials have been conducted to determine the potential benefits of vitamin D supplementation in preventing the conversion to diabetes, but the results are inconsistent. The aims of this study were to evaluate the current knowledge and to suggest recommendations for researchers on designing future trials regarding that matter. Methods: Four databases were searched for randomized control trials from the last 10 years about vitamin D and insulin resistance. The systematic electronic literature search identified 2645 studies, of which thirty-eight qualified for full-text reading and discussion. Finally, eight trials were included. Results: Final results of seven trials reported that supplementation of vitamin D does not reduce insulin resistance nor reduces the risk of diabetes mellitus type 2 development in prediabetes. Only one trial showed improvements in fasting glucose and HOMA-IR. Conclusions: Due to the great variation and biases in study designs, an unambiguous interpretation of the results is not possible. To eliminate those vulnerabilities in the future, we made certain suggestions for study design. Long-term and well-designed studies are still required.

Association of serum 25-hydroxyvitamin D levels, vitamin D-binding protein levels, and diabetes mellitus: Two-sample Mendelian randomization

“…[ 29 ] In contrast, a meta-analysis showed that vitamin D supplementation did not reduce insulin resistance or the risk of developing T2DM in prediabetic patients. [ 30 ] Rasouli et al showed that in non-vitamin D-deficient overweight or obese subjects at high risk of diabetes, vitamin D3 supplementation did not improve islet β-cell function but improved baseline 25(OH)D levels below 12 ng/mL in β-cell function in the population. [ 31 ] Meta-analyses and MR analyses have shown that vitamin D supplementation is not associated with a risk of T2DM but is associated with a reduced risk of all-cause mortality.…”

Effects of vitamin D supplementation on glucose and lipid metabolism in patients with type 2 diabetes mellitus and risk factors for insulin resistance

“…Recent studies[ 33 , 34 ] have revealed that approximately 50% of T2DM patients have vitamin D deficiency, and the level of vitamin D impacts insulin secretion, sensitivity and resistance. In this study, after vitamin D supplementation, the joint group showed more notable decreases in 2hPG, FBG, HbA1c and a more notable increase in 25(OH)D 3 than the conventional group.…”

Plant proteins: are they a good alternative to animal proteins in older people?

“…A healthy diet based on plant-source protein, typically plenty of fruit, vegetables, nuts, legumes, and cereals, has been presented as having a positive impact on older individuals [12,13]. Plant-based foods often have a low energy density because of their high fiber content, which confers beneficial effects against inflammation, insulin resistance, and weight loss [14]. For example, Shivakoti et al [15] recently demonstrated that dietary cereal fiber consumption by individuals aged 65 years and over had a favorable effect on inflammation by significantly reducing blood concentrations of C-reactive protein, interleukin-6 and interleukin-1 receptor antagonist (IL-1RA).…”