From the Journals

Vitamin D, omega-3 fatty acids do not preserve kidney function in type 2 diabetes



A new study has found that neither vitamin D nor omega-3 fatty acids are significantly more beneficial than placebo for prevention and treatment of chronic kidney disease in patients with type 2 diabetes, according to Ian H. de Boer, MD, of the University of Washington, Seattle, and coauthors.

Findings of the study were presented at Kidney Week 2019, sponsored the American Society of Nephrology, and published simultaneously in JAMA.

To determine the benefits of either vitamin D or omega-3 fatty acids in regard to kidney function, the researchers conducted a randomized clinical trial of 1,312 patients with type 2 diabetes. The trial was designed to accompany the Vitamin D and Omega-3 Trial (VITAL), which enrolled 25,871 patients to test the two supplements in the prevention of cardiovascular disease and cancer.

Participants in this study – known as VITAL–Diabetic Kidney Disease, designed as an ancillary to VITAL – were assigned to one of four groups: vitamin D plus omega-3 fatty acids (n = 370), vitamin D plus placebo (n = 333), omega-3 fatty acids plus placebo (n = 289), or both placebos (n = 320). The goal was to assess changes in in glomerular filtration rate estimated from serum creatinine and cystatin C (eGFR) after 5 years.

Of the initial 1,312 participants, 934 (71%) finished the study. At 5-year follow-up, patients taking vitamin D had a mean change in eGFR of −12.3 mL/min per 1.73 m2 (95% confidence interval, −13.4 to −11.2), compared with −13.1 mL/min per 1.73 m2 (95% CI, −14.2 to −11.9) with placebo. Patients taking omega-3 fatty acids had a mean eGFR change of −12.2 mL/min per 1.73 m2 (95% CI, −13.3 to −11.1), compared with −13.1 mL/min per 1.73 m2 (95% CI, −14.2 to −12.0) with placebo.

The authors noted that the modest number of measurements collected per participant limited the evaluation and analyses. In addition, the study focused broadly on the type 2 diabetes population and not on subgroups, “who may derive more benefit from the study interventions.”

In an accompanying editorial, authors Anika Lucas, MD and Myles Wolf, MD, of Duke University in Durham, N.C., said multiple clinical trials, including this latest study from de Boer and colleagues on kidney function, have failed to reinforce the previously reported benefits of vitamin D.

“The VITAL-DKD study population had nearly normal mean 25-hydroxyvitamin D levels at baseline, leaving open the question of whether the results would have differed had recruitment been restricted to patients with moderate or severe vitamin D deficiency,” they wrote (JAMA. 2019 Nov 8. doi: 10.1001/jama.2019.17302).

Nevertheless, it seems safe to conclude that the previous associations between vitamin D deficiency and adverse health were “driven by unmeasured residual confounding or reverse causality.

“Without certainty about the ideal approach to vitamin D treatment in advanced CKD, a randomized trial that compared cholecalciferol, exogenous 25-hydroxyvitamin D, and an activated vitamin D analogue vs. placebo could definitively lay to rest multiple remaining questions in the area,” they suggested.

The National Institute of Diabetes and Digestive and Kidney Diseases funded the study. The authors reported numerous potential conflicts of interest, including receiving grants, consulting fees, and equipment and supplies from various pharmaceutical companies and the National Institutes of Health. Dr. Wolf reported having served as a consultant for Akebia, AMAG, Amgen, Ardelyx, Diasorin, and Pharmacosmos. No other disclosures were reported.

SOURCE: de Boer IH et al. JAMA. 2019 Nov 8. doi: 10.1001/jama.2019.17380.

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