“Regarding anti-inflammatory effects of vitamin D and the fact that diabetes is more prevalent in vitamin D deficient subjects, vitamin D has been used in clinical trials for diabetic patients,” the researchers wrote in their study, published in the current issue of journal .
But they argued that existing studies have presented mixed results, and designed the meta-analysis to assess the effect of vitamin D on lipid profile of patients with type 2 diabetes.
Their analyses of 17 studies revealed that vitamin D had some effect on lipid profile in this population, and though the nutrient “cannot be considered as a main therapeutic agent for dyslipidemia [abnormal amount of lipids in the blood], it could be used as an adjuvant therapy along with other treatments for those patients.”
Selecting the studies
The researchers looked through seven databases: PubMed, Cochrane register of control trials, ISI Web of Science, Scopus, Google Scholar, Magiran, and Iran Medex. They selected randomized controlled trials published until November 2015 using search words along the lines of “cholecalciferol,” “type 2 diabetes,” and “vitamin D.”
The eligibility of a study was if it were a parallel-group RCT, in which consumption of a kind of vitamin D (as supplement or fortified food) was compared with placebo in patients with type 2 diabetes. All types of vitamin D (ergocalciferol, cholecalciferol, etc.) were considered.
Studies that looked at vitamin D intervention on non-type 2 diabetic patients or pre-diabetic patients were excluded. In the end, out of 2220 articles they considered, 17 were selected for the final meta-analysis.
Sample size and supplementation method
All the studies combined had a sample size of 1,365 participants (ranging from a study with 24 patients to a study with 183). Three studies analyzed fortified vitamin D as a delivery method, while the remaining 14 looked at supplementation.
Sub-analyses were made to see the effect of vitamin D on individual serums. Results of the 17 studies showed that vitamin D significantly reduced serum total cholesterol, reduced serum triglycerides (when patients received vitamin D < 2000 IU/d as well as in fortified foods), and reduced low-density lipoproteins.
However, the combination of studies showed that vitamin D did not significantly changed serum high-density lipoprotein in patients with type 2 diabetes, and most of the study results favored the control group.
Vitamin D may lower cardiovascular risk in patients with type 2 diabetes
“The overall results of the current meta-analyses revealed that vitamin D improved serum levels of total cholesterol, triglycerides, and low-density lipoprotein, while changes in serum high-density lipoprotein were negligible,” the researchers wrote.
Researchers added that studies in longer durations are needed to clarify the results of vitamin D’s role regarding high-density lipoproteins. “Our meta-analysis found a very slight but significant decrease in serum HDL (<1 mg/dl) in type 2 diabetic patients who received vitamin D,” they added. “Subjects with sufficient baseline serum vitamin D, or those who received vitamin D as supplements for 12 weeks or less, even showed detrimental results (∼1 mg/dl reduction).”
Source: Clinical Nutrition
Published online ahead of print, http://dx.doi.org/10.1016/j.clnu.2016.03.001
"Effects of vitamin D on serum lipid profile in patients with type 2 diabetes: A meta-analysis of randomized controlled trials"
Authors: Tina Jafari, Aziz A. Fallah Afshin Baranid