medwireNews: Neither vitamin D nor omega-3 fatty acids are able to slow the decline in kidney function for people with type 2 diabetes, show the results of the VITAL-DKD trial.
This study enrolled a subset of 1312 people who had type 2 diabetes and were participating in the VITAL randomized trial, which tested the effects of vitamin D3 and omega-3 fatty acid supplementation on cardiovascular and cancer outcomes.
The main VITAL trial found no benefits of supplementation on these outcomes, and VITAL-DKD follows suit, with neither intervention showing any effect on the change in estimated glomerular filtration rate (eGFR) after 5 years of follow-up.
The study participants were aged an average of 67.6 years, 46% were women, and the median diabetes duration in the randomized treatment groups ranged from 6 to 10 years. Average baseline eGFR was 85.8 mL/min per 1.73 m2, declining to 73.5 mL/min per 1.73 m2 at year 5.
This decline is “more than expected with aging alone,” write report Ian de Boer (University of Washington, Seattle, USA) and co-researchers in JAMA, noting that it “probably reflects cumulative effects of relatively long-standing type 2 diabetes.”
In the vitamin D part of the study, kidney function declined by 12.3 versus 13.1 mL/min per 1.73 m2 for the supplementation versus placebo groups; the corresponding values in the omega-3 part of the study were 12.2 versus 13.1 mL/min per 1.73 m2. There were no significant differences between the intervention and placebo groups.
Supplementation also had no effect on secondary outcomes such as the albumin-to-creatinine ratio, or the composite of a 40% decline in kidney function, kidney failure, or death.
In a linked editorial, Anika Lucas and Myles Wolf, both from Duke University School of Medicine in Durham, North Carolina, USA, say that the results “do not completely preclude future investigation of vitamin D and [chronic kidney disease] outcomes,” noting that the supplementation might prove to be beneficial in people with insufficient or deficient baseline levels, or with more advanced kidney disease.
However, they stress that the contrast between the positive epidemiologic trials and the negative randomized controlled trials of vitamin D “offers a stark lesson on the chasm between association and causation.”
They add: “It now seems safe to conclude that many prior epidemiological associations between vitamin D deficiency and adverse health outcomes were driven by unmeasured residual confounding or reverse causality.”
The editorialists conclude: “With each new and carefully conducted negative trial of vitamin D supplementation, the Institute of Medicine’s 2010-2011 report that emphasized the bone benefits of attaining sufficient vitamin D stores over other theoretical benefits based on observational data looks ever more prescient.”
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JAMA 2019; doi:10.1001/jama.2019.17380
JAMA 2019; doi:10.1001/jama.2019.17302