Osteopenia and circulating levels of vitamin D metabolites in diabetes mellitus

Vitamin D Deficiency Is Inversely Associated with Homeostatic Model Assessment of Insulin Resistance

The study was conducted to comprehensively assess the association of the concentration of vitamin D in the blood and insulin resistance in non-diabetic subjects. The objective was to pool the results from all observational studies from the beginning of 1980 to August 2021. PubMed, Medline and Embase were systematically searched for the observational studies. Filters were used for more focused results. A total of 2248 articles were found after raw search which were narrowed down to 32 articles by the systematic selection of related articles. Homeostatic Model Assessment of Insulin Resistance (HOMAIR) was used as the measure of insulin resistance and correlation coefficient was used as a measure of the relationship between vitamin D levels and the insulin resistance. Risk of bias tables and summary plots were built using Revman software version 5.3 while Comprehensive meta-analysis version 3 was used for the construction of forest plot. The results showed an inverse association between the status of vitamin D and insulin resistance (r = -0.217; 95% CI = -0.161 to -0.272; p = 0.000). A supplement of vitamin D can help reduce the risk of insulin resistance; however further studies, like randomized controlled trials are needed to confirm the results.

Insulin Resistance Is Inversely Associated with the Status of Vitamin D in Both Diabetic and Non-Diabetic Populations

Vitamin D has been implicated in the regulation of glucose metabolism and insulin resistance. We designed this study to provide evidence that insulin resistance is dependent on the concentration of vitamin D in the body. Forty observational studies of both type 2 diabetes mellitus patients and healthy subjects were included in this meta-analysis. Related articles were searched from Embase, PubMed, and Medline through January 2021. Filters for search were used to obtain more focused results. We used Comprehensive Meta-Analysis Version 3 for the construction of forest plots. RevMan software version 5.3 was used to build the risk of bias tables and summary plots. The observational studies included in this systematic review and meta-analysis showed an inverse relationship of insulin resistance with the status of vitamin D both in non-diabetic (r = -0.188; 95% CI = -0.141 to -0.234; p = 0.000) and diabetic (r = -0.255; 95% CI = -0.392 to -0.107, p = 0.001) populations. From the meta-analysis we concluded that hypovitaminosis D is related to increased levels of insulin resistance in both type 2 diabetes patients and the healthy population all over the world.

The role of vitamin D in the metabolic homeostasis of diabetic bone

Most studies across a variety of geographic locations suggest that vitamin D insufficiency is more common in individuals with type 1 diabetes (T1D) compared to the general population. In type 2 diabetes (T2D), while obesity is commonplace and lower vitamin D levels are present in obese adolescents and adults, the association between vitamin D insufficiency and T2D is less clear. Studies suggest that the relationship between T2D and vitamin D may be concurrently influenced by ethnicity, geography, BMI and age. None-the-less, diabetic osteopathy is a significant co-morbidity of both forms of diabetes, and is characterized by micro-architectural changes that decrease bone quality leading to an increased risk for bone fracture in both disorders. The question remains, however, to what degree vitamin D homeostasis contributes to or exacerbates skeletal pathology in diabetes. Proposed mechanisms for vitamin D deficiency in diabetes include: 1) genetic predisposition (T1D); 2) increased BMI (T2D); 3) concurrent albuminuria (T1D or T2D); or 4) exaggerated renal excretion of vitamin D metabolites or vitamin D binding protein (T1D, T2D, animal models). The specific effects of vitamin D treatment on diabetic osteoporosis have been examined in rodents, and demonstrate skeletal improvements even in the face of untreated diabetes. However, human clinical trial data examining whether vitamin D status can be directly related to or is predictive of bone quality and fracture risk in those with diabetes is still needed. Herein, we provide a review of the literature linking vitamin D, diabetes and skeletal health.

Different effects of insulin and insulin-like growth factors I and II on osteoprogenitors and adipocyte progenitors in fetal rat bone cell populations

We investigated the effects of insulin (1-1,000 nM), insulin-like growth factor (IGF)-I, and IGF-II (3-100 nM each) alone or together with 10 nM dexamethasone (DEX) or 10 nM 1,25-dihydroxyvitamin D(3) (1,25[OH](2)D(3)) on proliferation and differentiation of adipocyte and osteoblast progenitors in bone cell populations derived from fetal rat calvaria. The effects on differentiation were evaluated by counting the number of bone or osteoid nodules and adipocyte colonies and the effects on proliferation, by measuring their size by image analysis. The types of cells studied were 1,25(OH)(2)D(3)- and DEX-responsive adipocyte progenitors and DEX-dependent and independent osteoprogenitors. Both IGF-I and IGF-II stimulated osteoprogenitor differentiation both alone and in the presence of DEX, while insulin stimulated osteoprogenitor differentiation only in the absence of DEX. Neither IGF-I/-II nor insulin affected proliferation of osteoprogenitors. Insulin had little effect on adipocyte differentiation by itself but strongly stimulated differentiation in the presence of either 1,25(OH)(2)D(3) or DEX, while IGF-II stimulated adipocyte differentiation in both the absence and presence of 1,25(OH)(2)D(3) or DEX. IGF-I by itself or in the presence of DEX strongly stimulated adipocyte cell differentiation but had little effect in the presence of 1,25(OH)(2)D(3). Our results demonstrate that insulin, IGF-II, and IGF-I have specific and different effects on the differentiation and proliferation of different groups of progenitor cells.