الفهرس 
VITAMIN DOnly 14 pages are availabe for public view
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Abstract
D
iabetes is one of the leading causes of morbidity and mortality worldwide. Although all the efforts are aiming at secondary prevention of the disease but that does not completely eliminate the risk of complications, that is why working at the level of primary prevention in prediabetic subjects appears to be the golden opportunity for risk elimination. Although the main role of vitamin D is to maintain calcium and phosphorus homeostasis and promote bone mineralization, recent evidence suggests that it may also be a promising modifier of diabetes risks.
American Diabetes Association defines prediabetes as impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT). People with prediabetes are at relatively high risk of developing T2DM. The pathogenesis of prediabetes involves insulin resistance and defective β-cell function for secreting insulin. Consequently, interventions that have a role in preserving β-cell function and in ameliorating insulin resistance are most likely to slow prediabetes progression to diabetes.
Emerging evidence suggests that vitamin D may play a role in the prevention of diabetes development. An indicator of vitamin D status, 25-hydroxyvitamin D [25(OH)D], has been reported to be inversely related to the risk of diabetes. Also, it has been proven in several studies that the progression to diabetes in subjects with low 25(OH)D level was greater than in those who had a high 25(OH)D level.
Vitamin D receptors have been identified in many organs that are involved in glucose metabolism, such as pancreatic β-cell muscle, adipose tissue and liver. Low vitamin D levels have, therefore, been postulated to be associated with insulin resistance, resulting in diabetes.
It has been hypothesized that vitamin D had an effect on insulin resistance and β-cell function. Binding of vitamin D and vitamin D receptors may enhance the transcriptional activation of the insulin gene and increase the synthesis of insulin. It also stimulates the expression of insulin receptors and activation of glucose transporters. Alternatively, an indirect effect of vitamin D may be mediated via regulating calcium concentration in β cells resulting in an enhancement in insulin secretion. Calcium is also essential for the insulin-mediated intracellular process in insulin target tissues.
Several randomized controlled trials have been conducted to evaluate the effects of vitamin D supplementation in prediabetes, but the results are conflicting. The aim of the present study, therefore, was to perform a systematic review and meta-analysis in an attempt to delineate the role of vitamin D supplementation on insulin resistance and glycemic control in prediabetes.
• Aim of the study:
To evaluate the effect of vitamin D on insulin resistance and glycaemic control in prediabetes.
• Patients and Methods:
Our meta-analysis included 13 studies; all were Randomized placebo-controlled trials, we included the studies compliant to our inclusion criteria and were published till December 2022.
In all the included studies Vitamin D administration or it’s analogues were used as the intervention in pre-diabetic patients, versus placebo.
Participants were adult patients (≥18years old) with diagnosis of prediabetes. Patients were considered to have definite diagnosis of prediabetes if they were laboratory-confirmed using fasting blood glucose (FBG) and/or 2-h plasma glucose after an oral glucose tolerance test (OGTT) and glycosylated haemoglobin (HbA1c).
Meta-analysis was performed using MedCalc Statistical Software version 19.0.5 (MedCalc Software bvba, Ostend, Belgium; https://www.medcalc.org; 2019). For assessment of heterogeneity of the included studies I2 values and Q-test were used. Forest plots with random-effects (for high heterogeneity) and fixed effects (for low to moderate heterogeneity) models were used in the current study. The estimates were pooled using inverse variance random-effects model and presented as standardized mean difference and 95% confidence intervals (CIs). P value less than 0.05 was considered statistically significant.
• Conclusion:
In this systematic review we have summarized existing knowledge regarding the role of vitamin D supplementation on progression from prediabetes to overt T2DM.
Our meta-analysis of thirteen interventional randomized controlled trials suggests that vitamin D supplementation reduced the risk of new-onset T2DM. Similarly, our meta-analysis indicated that vitamin D treatment might boost the rate at which prediabetes returns to normal.
Additionally, our findings showed that vitamin D supplementation in pre-diabetics with vitamin D deficiency was linked to lower HbA1c, FBG and 2-hours post prandial OGTT levels.
There are many possible mechanisms that could explain effect of vitamin D and calcium on glycemic control, even though the effect size for vitamin D is not comparable to the effect of metformin or other glycemic control medications, over a long period of time and when administered at the population level, vitamin D supplementation may offer an affordable, safe, and accessible preventive measure.
Despite the positive outcome of our meta-analysis there are several studies with conflicting results, Therefore, we are surely looking forward to larger randomized controlled trials to evaluate role of 25 (OH) vitamin D as a promising agent in controlling glycemic indices