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 in the Journal of the American Medical Association.
Rather than reducing the risk of heart attack and stroke, the vitamins appear to actually increase it, the researchers said in April.
It is thought that at least 40 percent of diabetics 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 thought they would improve kidney function.
A team headed by Dr. David Spence of the University of Western Ontario in London (Canada) 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.