Diabetics with kidney disease who are taking high doses of B vitamins in an
effort to forestall heart attacks should stop taking them immediately because
they are potentially very harmful, Canadian researchers reported Tuesday in the
Journal of the American Medical Assn. Rather than reducing the risk of heart
attack and stroke, the vitamins appear to actually increase it, the researchers
said.
An estimated 21 million Americans and 3 million Canadians have either Type 1 or
Type 2 diabetes, and it is thought that at least 40% of them will develop
diabetic nephropathy, in which the function of the kidneys is impaired.
Diabetics typically have above-normal levels of the amino acid homocysteine in
their blood, and elevated levels are associated with an increased risk of heart
disease. B vitamins normally reduce homocysteine levels, and researchers had
also though they would improve kidney function.
A
team headed by Dr. David Spence of the University of Western Ontario in London
organized a clinical trial in which researchers hoped to demonstrate a benefit
from the supplement. They enrolled 238 diabetic patients at five Canadian
medical centers. Half received a daily dose of 2.5 milligrams of folic acid, 25
milligrams of vitamin B6 and 1 milligram of vitamin B12 and half received a
placebo.
After an average of 32 months, the researchers found that those taking the
vitamins had a significantly higher decrease in kidney function, as measured by
the ability to filter toxic wastes from the bloodstream. Moreover, eight people
taking the vitamins suffered a heart attack, compared with four taking the
placebo; and six taking the vitamins suffered a stroke, compared to one taking
the placebo. Spence said he was greatly surprised by the results and initially
thought that researchers had mixed up the data. He noted that the vitamins are
normally excreted in urine and speculated that kidney damage produced by the
diabetes led to a toxic buildup of the supplement in the patients. The B
vitamins included in multivitamin supplements should not be a problem, he added.
He said that researchers would have to find a different way to reduce
homocysteine levels.
The study was funded by the Canadian Institutes of Health Research and the
Kidney Foundation of Canada. The vitamins and placebos were donated by Pan
American Laboratories.
