Many studies have shown that vitamin D plays a renal protective role, as supplementation is expected to delay the progression of diabetic kidney disease, however, results from previous studies suggest otherwise. To determine whether vitamin D supplements offer kidney-related benefits for individuals with high diabetes risk, researchers conducted a clinical trial recently that examined the potential of vitamin D to support kidney health of individuals with pre-diabetes.
Because low blood vitamin D levels have been linked to higher risks of type 2 diabetes and kidney disease, researchers conducted a secondary analysis of the Vitamin D and type 2 diabetes study to evaluate the effects of vitamin D supplementation on kidney health in individuals with pre-diabetes—a condition that increases risk for type 2 diabetes, the leading cause of kidney disease.
The D2d study
The study, published in Clinical Journal of the American Society of Nephrology, randomized 2,423 adults with overweight/obesity and pre-diabetes to vitamin D3 4000 IU per day or placebo, for a median treatment duration of about 3 years.
"The D2d study is unique because we recruited individuals with high-risk pre-diabetes, having 2-out-of-3 abnormal glucose values, and we recruited more than 2,000 participants, representing the largest vitamin D diabetes prevention trial to date," noted lead author Sun H. Kim, MD, MS of Stanford University School of Medicine.
During the trial, there were 28 cases of kidney function worsening in the vitamin D group and 30 in the placebo group, and the average change in kidney function during follow-up was similar in both groups.
"Our results did not show a benefit of vitamin D supplements on kidney function. About 43% of the study population was taking outside-of-study vitamin D, up to 1000 IU daily, at study entry, though. Among those who were not taking any vitamin D on their own, there was a suggestion for vitamin D lowering the amount of urine protein over time, which means that it could have a beneficial effect on kidney health. Additional studies are needed to look into this further," Kim said.
Deficiency may have been a factor
Kim added that vitamin D supplementation is popular, and it's difficult for clinical trials of vitamin D supplementation to show a benefit if the population studied is not vitamin D deficient.
"The majority of the study population had sufficient blood vitamin D levels and normal kidney function," Kim said. "Benefits of vitamin D might be greater in people with low blood vitamin D levels and/or reduced kidney function."
Source: Clinical Journal of the American Society of Nephrology
(2021) DOI: 10.2215/CJN.00420121
“Effect of Vitamin D Supplementation on Kidney Function in Adults with Prediabetes”
Authors: S.H. Kim et al.