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NEW YORK (Reuters Health) - In patients with diabetic nephropathy, high doses of B vitamins accelerate kidney dysfunction and increase the rate of myocardial infarction (MI) and strokes, according to a Canadian study.

B vitamins are used to lower high plasma levels of homocysteine, which is linked to an elevated risk for diabetic nephropathy and vascular diseases, the authors explain in the April 28th Journal of the American Medical Association. But previous research has suggested either a neutral effect or even potential harm from B vitamins.

The multicenter, double-blinded DIVINe trial, conducted between 2001 and 2007, enrolled 238 patients with diabetic nephropathy. Senior author Dr. J. David Spence, from the University of Western Ontario, London, and colleagues randomly assigned patients to treatment with a single daily tablet containing 2.5 mg folic acid, 25 mg vitamin B6 and 1 mg vitamin B12, or to placebo.

A total of 118 subjects completed the 36-month follow-up, but 119 subjects in each group were included in the modified intention-to-treat analyses.

Subjects in the B-vitamin group had a “much greater” decrease in radionuclide glomerular filtration rate (GFR) than the placebo group, the authors report. At 36 months, GFR had fallen by a mean of 16.5 vs 10.7 mL/min/1.73 m2 in the vitamin vs placebo groups, respectively (p = 0.02).

Dr. Spence and associates also observed a significantly greater difference in the 36-month risk of the composite endpoint (MI, stroke, revascularization, and all-cause mortality). There were 13 events (14.4%) in the placebo group and 24 events (23.5%) in the vitamin group, for a hazard ratio of 2.0 (p = 0.04).

There was no significant difference between groups in the proportion of participants who required dialysis or in mean glycated hemoglobin, and proteinuria did not change significantly. Also, the treatment arms were similar in rates of all-cause mortality, amputation and cognitive decline.

The authors suggest that “B vitamins were in some way associated with both renal and vascular toxicity.” They note that the vitamins are metabolized in the kidneys, so vitamin toxicity may be more of a problem in patients with impaired renal function.

They conclude, “It would be prudent to discourage the use of high-dose B vitamins as a homocysteine-lowering strategy outside the framework of properly conducted clinical research.”

Reference:
JAMA 2010;303:1603-1609.

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