Vitamin D beneficial against T1DM, T2DM and gestational diabetes: Systematic review
Researchers at Iran's Mashhad University of Medical Sciences, Shahrekord University of Medical Sciences, Ferdowsi University, Islamic Azad University and Babol University of Medical Sciences, as well as the UK's Brighton & Sussex Medical School, conducted a systemic review and meta-analysis to evaluate the impact of vitamin D supplements on glycaemic control indices.
They assessed insulin resistance (HOMA-IR), glycated haemoglobin (HbA1C), fasting blood glucose (FBG) and quantitative insulin-sensitivity check index (QUICKI), as well as lipid profile in diabetic patients.
They searched eight databases for RCTs or cross-sectional and cohort studies that had been published up to December 2017 and used comprehensive meta-analysis software (CMA) for all statistical analyses.
D against diabetes
They eventually settled on 82 studies, 37 of which were used for the meta-analysis.
They then reported that vitamin D supplementation was linked to significant improvement in FBG and HbA1C in patients with type 2 diabetes mellitus (T2DM), although similar statistically significant changes were not seen in women with gestational diabetes (which affects approximately 4.7% of pregnant women in Iran).
However, treatment using vitamin D supplements led to an improvement in HOMA-IR in women with gestational diabetes, as well as in individuals with T2DM.
At the same time, the researchers found that the pooled result of the cross-sectional meta-analysis showed that serum vitamin D concentration was significantly lower in diabetics than in healthy controls.
These results were supported by earlier research, where vitamin D supplementation had exhibited "potentially beneficial effects" via an improvement in glucose tolerance test (GTT) and a reduction in the prevalence of gestational diabetes — diabetic pregnant women who had consumed vitamin D saw improved glycaemic status measurements and HbA1C levels, with no complications reported.
When it came to type 1 diabetes mellitus (T1DM), they reported that vitamin D supplementation played a "potentially important role" by suppressing T-cell activation and improving HbA1C and FBG.
Vitamin D supplementation was also recommended in conjunction with other types of supplementation, such as calcium. The combination was found to lower T2DM risk, and have a positive effect on BMI, hip circumference and systolic blood pressure in T2DM patients.
On the other hand, some of the studies showed that vitamin D supplementation did not affect insulin resistance or FBG, and reported no significant association between gestational diabetes and serum vitamin D levels.
First and future indications
The researchers stated that the current review was the first meta-analysis to evaluate the impact of vitamin D on glycaemic indices in "diverse subgroups of diabetes, and also summarises cross-sectional, cohort and interventional studies in diabetic patients".
They also noted, however, a "major limitation": the lack of pre- and post-baseline measures for glycaemic indices, as observed in several papers, which meant they had to be excluded from the meta-analysis.
In conclusion, they wrote: "This systematic and meta-analysis review demonstrated that vitamin D had major effects on (the) FBG of type 2 diabetics and pregnant women with diabetes. Therefore, vitamin D could be used as an adjuvant therapy along with the other treatments for those patients.
"Also, vitamin D supplementation leads to an improvement in HOMA-IR, FBG and HbA1C. Furthermore, the overall pooled result of the cross-sectional meta-analysis showed the level of vitamin D is significantly lower in diabetic patients than healthy controls.
However, further studies are required to better understand the relationship between vitamin D supplementation and glucose homeostasis indices in type 2 diabetes patients and pregnant diabetic women."
Source: Complementary Therapies in Clinical Practice
"The effects of vitamin D supplementation on indices of glycemic control in Iranian diabetics: A systematic review and meta-analysis"
Authors: Reza Sahebi, et al.