No Kidney Benefit from Vitamin D Supplementation in Patients with Prediabetes

Sun Kim, MD

Data from a secondary analysis of a clinical trial examining use of vitamin D supplementation suggests vitamin D supplementation had no significant effects on kidney health.

An analysis of data from patients with prediabetes but without vitamin D insufficiency from the Vitamin D and type 2 diabetes (D2d) study, results demonstrate vitamin D supplementation did not impact progression of kidney of function decline and was not associated with a meaningful effect on change in UACR or eGFR.

“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,” said Sun H. Kim, MD, MS, an endocrinologist and associate professor of medicine at Stanford University School of Medicine, in a statement. “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.”

Few, if any, supplements have ever been examined or discussed to the same extent as vitamin D. Often hailed as a panacea by social media influencers, the promise of vitamin D is something that has been the subject of multiple clinical trials and observational studies. One of those trials was the D2d study, which was a multi center trial enrolling more than 2400 participants from 22 cities in the US. Designed with the intent of assessing whether vitamin D supplementation could slow the onset of type 2 diabetes, the trial randomized patients to receive 1000 IU of vitamin D or no vitamin D supplementation.

The current study was designed to assess the effect of vitamin D supplementation on kidney outcomes in patients considered to have prediabetes from within the D2d study. Of the more than 2400 included in the original D2d study, 2166 were included in the secondary analysis performed by Kim and colleagues.

“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,” Kim noted.

Outcomes of interest for the analyses included worsening kidney function and changes in eGFR and UACR. For the purpose of analysis, worsening in kidney disease was calculated using the Kidney Disease: Improving Global Outcomes (KDIGO ) risk score recorded at consecutive follow-up visits.

The 2166-patient cohort had a mean age of 60 years, a mean BMI of 32 kg/m2, a mean serum 25(OH)D of 28 ng/ml, and 79% had hypertension. Additionally, the mean eGFR was 87 mL/min/1.73m2, the mean UACR was 11 mg/g, and 10% had a KDIGO risk score considered moderate or greater.

During a follow-up period lasting median of 2.9 years, a total of 28 cases of worsening KDIGO occurred in the vitamin D arm compared to 30 among those in the placebo arm (HR, 0.89; 95% CI, 0.52-1.52). Analysis indicated the mean difference in eGFR from baseline was -1.0 ml/min/1.73m2 (95% CI, —1.3 to —0.7) among the vitamin D arm and —0.1 ml/min/1.73m2 (95% CI, —0.4 to 0.2) among the placebo arm, with a between-group difference of −1.0 ml/min/1.73m2 (95% CI, —1.4 to —0.6).

When assessing changes in UACR, results indicated a mean difference from baseline of 2.7 mg/g (95% CI, 1.2 to 4.3) among the vitamin D arm and 2.0 mg/g (95% CI, 0.5 to 3.6) among the placebo arm, with a between-group difference of 0.7 mg/g (95% CI, —1.5 to 2.9).

This study, “Effect of Vitamin D Supplementation on Kidney Function in Adults with Prediabetes: A Secondary Analysis of a Randomized Trial,” was published in the Clinical Journal of the American Society of Nephrology.