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Analysis finds vitamin D supplementation potentially beneficial for type 2 diabetes

A meta-analysis suggests that vitamin D supplementation reduces fasting plasma glucose and HbA1c levels in patients with type 2 diabetes

Vitamin D supplementation may be of value to patients with type 2 diabetes, especially if they have suboptimal levels of the vitamin according to a meta-analysis undertaken by US and Iranian researchers.

It has been estimated that in 2017, a staggering 462 million individuals had type 2 diabetes, corresponding to just over 6% of the global population. While there are several therapies available for the management of type 2 diabetes, new treatments will always be needed, given the high prevalence of the disorder. One such potential treatment is vitamin D supplementation and while this is usually given to regulate calcium and phosphorus levels, in recent years, a purported role has been suggested for several diseases. For example, data from the prospective Nurses’ Health study found that higher vitamin D and calcium intake was associated with a 33% lower risk of type 2 diabetes. Nevertheless, studies that involved actual vitamin D supplementation produced mixed findings. For example, one study 6-month trial found that supplementing with the vitamin in patients with type 2 diabetes, failed to affect either insulin sensitivity or secretion. In contrast, an 8-week intervention study demonstrated significant reductions in fasting plasma glucose, insulin and HOMA-IR.

As a result, in the current study, researchers performed a meta-analysis to examine the effect of using the vitamin on indices of glycaemic control including fasting plasma glucose (FPG), HbA1c and HOMA-IR.

Vitamin D supplementation and glycaemic measures

A total of 46 eligible trials were identified including 4,313 patients with type 2 diabetes and a mean age of 56.5 years and of whom 2,164 received the vitamin intervention. The majority of the studies (42) used an oral supplement, whereas in four trials, it was given via intramuscular injection.

The pooled analysis for HbA1c showed a significant reduction compared to placebo for vitamin D (weighted mean difference, WMD = -0.20, p < 0.001). Similarly, there was a significant reduction in FPG (WMD = -0.28 mmol/L, p < 0.001) and HOMA-IR (WMD = -0.42, p = 0.019) in those given vitamin D.

The authors concluded that although vitamin D supplementation had a positive impact of glycaemic indices, they cautioned that the substantial heterogeneity between the included studies, raised the possibility of publication bias.

Farahmand MA et al. What is the impact of vitamin D supplementation on glycemic control in people with type-2 diabetes: a systematic review and meta-analysis of randomized controlled trails. BMC Endocr Disord 2023