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Study Links High-Dose B Vitamins With Kidney Decline in People With Kidney Disease

Diane Fennell

May 7, 2010

A number of studies have demonstrated a link between high blood concentrations of homocysteine, an amino acid that’s produced by the body, and the risk of developing conditions such as diabetic nephropathy (kidney disease), retinopathy (eye disease), and vascular conditions such as heart attack and stroke. Treatment with B vitamins has been shown to decrease the concentration of homocysteine in the blood, so researchers wondered whether therapy with B vitamins could, by extension, slow the progression of kidney disease and prevent complications affecting the blood vessels.

To test this out, scientists in Ontario, Canada, randomly assigned 238 people with Type 1 or Type 2 diabetes and diabetic nephropathy to be given either a single daily tablet containing 2.5 milligrams of folic acid, 25 milligrams of vitamin B6, and 1 milligram of vitamin B12, or a placebo (inactive) tablet. Participants had homocysteine levels and glomerular filtration rate (GFR; an indicator of kidney function) measured at follow-up visits every six months for up to three years.

The B vitamins appeared to be successful at lowering blood levels of homocysteine. However, this decrease did not translate into better health outcomes — in fact, the researchers found that people who had received B vitamins had a greater decrease in GFR, corresponding to poorer kidney function, than those who had received placebo and also had twice the rate of heart attack, stroke, and all-cause deaths at the end of the follow-up period.

The researchers speculate that the beneficial effect of lowering homocysteine levels might have been offset by toxicity associated with the B vitamins. According to author J. David Spence, MD, and colleagues, “Because B vitamins are water soluble, we suspect that while healthy people would excrete excess vitamins in urine, those with renal failure would not be able to do so, perhaps causing the adverse effects we have seen in this study. Vitamin B therapy may still be beneficial in people with normal kidney function, but this is clear evidence that high doses of vitamin B should not be given to those with kidney problems.”

To learn more, read the article “High Doses of B Vitamins Associated With Increased Decline in Kidney Function for Patients With Kidney Disease from Diabetes” or see the study’s abstract in the Journal of the American Medical Association.



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