Vitamin D, Fish Oil Don’t Prevent Kidney Disease in Diabetes

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 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? 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. 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.” 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.” 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.

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