Can vitamin B12 reduce stroke risk?

A commentary by Dr. David Spence of The University of Western Ontario and Dr. Meir Stampfer of the Harvard School of Public Health in today's Journal of the American Medical Association (JAMA) argues that vitamin therapy still has a role to play in reducing stroke.

Vitamin B therapy was once widely used to lower homocysteine levels. Too much of this amino acid in the bloodstream was linked to increased risk of stroke and heart attack. But several randomized trials found lowering homocysteine levels with B vitamins did not result in a cardiovascular benefit. And a study by Dr. Spence, a scientist with the Robarts Research Institute at Western's Schulich School of Medicine & Dentistry, found Vitamin B therapy actually increased cardiovascular risk in patients with diabetic nephropathy.

Dr. Spence says this commentary provides insights that overturn the widespread belief that "homocysteine is dead." He says two key issues have been overlooked in the interpretation of the clinical trials: the key role of vitamin B12, and the newly recognized role of renal failure.

"It is now clear that the large trials showing no benefit of vitamin therapy obscured the benefit of vitamin therapy because they lumped together patients with renal failure and those with good renal function. The vitamins are harmful in renal failure, and beneficial in patients with good renal function, and they cancel each other out," says Dr. Spence, the author of "How to Prevent Your Stroke." The authors also contend most of the trials did not use a high enough dose of vitamin B12.