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Does Vitamin D Supplementation Promote Kidney Function in Patients with Prediabetes?

LOW vitamin D in the blood has been associated with an increased risk of various diseases including Type 2 diabetes mellitus and kidney disease. A recent clinical trial carried out by Sun H. Kim, Stanford University School of Medicine, California, USA, examined the potential benefits of vitamin D supplementation for protecting the kidney health of individuals with prediabetes. Prediabetes is a condition that increases the risk of developing Type 2 diabetes mellitus, which is the leading cause of kidney disease. 

In this randomised trial, 2,423 adults with prediabetes and diagnosed as overweight or obese were treated with either vitamin D3 (4,000 IU/day) or a placebo, for a medium treatment duration of 2.9 years. The adults recruited were classified as high-risk, with 2/3 abnormal glucose values. Kim described the study as “representing the largest vitamin D diabetes prevention trial to date.” 

Throughout the trial, the kidney function of 28 participants in the vitamin D group declined alongside 30 participants in the placebo group. Furthermore, the average change in kidney function during the study’s follow-up was similar between the two groups and therefore did not demonstrate a benefit of the vitamin D supplements. Kim explained the difficulties of demonstrating the benefits of vitamin D supplementation in a population that is not vitamin D deficient: “The majority of the study population had sufficient blood vitamin D levels and normal kidney function. Benefits of vitamin D might be greater in people with low blood vitamin D levels and/or reduced kidney function.” 

Vitamin D supplementation amongst the general population is popular and approximately 43% of the participants were found to be self-medicating with out-of-study vitamin D (up to 1,000 IU/day) at the study’s inception. Amongst the study population who were not self-medicating, there were suggestive results that vitamin D decreased urine protein production and could therefore hold beneficial effects for kidney health and function. Future studies are needed to examine these effects further.