Vitamin D Strikes Out Again, This Time Failing to Protect Kidney Function in People with Diabetes

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The nationwide study tells us we should be looking outside of the supplement aisle when it comes to treating diabetes.

It was Kidney Week — the annual meeting of the American Society of Nephrology last week and 14,000 practitioners descended on the nations capital to discuss the latest developments in the field.

So it is in the spirit of homeostasis that I want to talk about one study, appearing now in the Journal of the American Medical Association, which answered a question we’d all been wondering: could a cheap, widely available dietary supplement alter the course of kidney decline in people with diabetes?

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Factorial design. Two trials for the price of 1.5.

In a wonderful bit of factorial design, the trial actually examined 2 supplements — vitamin D in the form of 2000 IU/ day of cholecalciferol and fish oil — omega-3 fatty acid.

Now, Vitamin D is like the Charlie Brown of supplements. We keep setting it up for a big kick of the clinical trial football, and, invariably, Vitamin D ends up falling flat.

And to mix sports metaphors, there was no joy in Mudville as Vitamin D struck out. Nephrologists have been pushing Vitamin D on our patients for years without, dare I say, a whole lot of evidence. This was one we hoped would work.

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No help from fish oil either, as you can see here. The boxes show how eGFR changed over the course of the study in the control and intervention patients. You’ll note a pretty significant decline of around 12 ml/min over the 5 year study, marking just how seriously we need to take kidney function in patients with diabetes. But in terms of differences? Nothing. No benefit from Vitamin D. No benefit from fish oil.

I caught up with lead author Dr. Ian De Boer at Kidney Week and asked him, given these results, would he advise his diabetic patients to take Vitamin D or Fish oil?

“It’s important not to dispel hope from people and not discourage them from taking care of themselves and looking for good ways to take care of themselves. But this is not going to be an effective way. And there are better ways for people with type two diabetes to prevent kidney disease.” Lead Author Ian De Boer, MD MS. Professor, Nephrology. University of Washington.

Now this trial was a bit special — it was particularly decentralized. A single center in Massachussetts ran the study, but it was done almost entirely by mail and telephone, with patients across the US sending their blood and urine into the research center. This, obviously, led to a bit higher loss to follow-up than we might like to see — about 30% — and that could muddy the waters of the final results to obscure any potential benefit. I asked Dr. De Boer if he was worried about that.

“We used I think, reasonable statistical techniques to account for the missing data and multiple imputation. And we performed sensitivity analysis, complete case analysis, looking at only the people who provided all the samples and the results were identical.” Lead Author Ian De Boer, MD MS. Professor, Nephrology. University of Washington.

In other words, there’s probably nothing here.

But this is not a bad thing. This was a high quality trial that tells us that we don’t need to focus our energies here. Our patients have enough to do without worrying about which supplements they should take. With Vitamin D and fish oil off the playing field, we can focus more on glucose and blood pressure control, high-quality diet, and exercise. Not as easy as running down to the local Vitamin Shoppe, but then, nothing worthwhile ever is.

This commentary first appeared on

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Writing about medicine, science, statistics, and the abuses thereof. Commentator at Medscape. Associate Professor of Medicine at Yale University.

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