The Charlie Brown of Supplements Strikes Out Again

F. Perry Wilson, MD, MSCE


November 13, 2019

Welcome to Impact Factor, your weekly dose of commentary on a new medical study. I'm Dr F. Perry Wilson.

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

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've all been wondering about: Could a cheap, widely available dietary supplement alter the course of kidney decline in people with diabetes?

In a wonderful bit of factorial design, the trial actually examined two 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.

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 the lead author, Dr Ian de Boer, at Kidney Week and asked him whether, given these results, he would advise his patients with diabetes to take vitamin D or fish oil.


Now, this trial was a bit special; it was particularly decentralized. A single center in Massachusetts ran the study, but it was done almost entirely by mail and telephone, with patients across the United States sending their blood and urine to 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.


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 shop, but then, nothing worthwhile ever is.

F. Perry Wilson, MD, MSCE, is an associate professor of medicine and director of Yale's Program of Applied Translational Research. His science communication work can be found in the Huffington Post, on NPR, and here on Medscape. He tweets @methodsmanmd and hosts a repository of his communication work at

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