Vitamin B therapy dangerous for millions of diabetics with kidney disease

The use of vitamin B to stop kidney damage in people with diabetes needs a closer look, and those with kidney damage now taking high vitamin B doses, should stop. That is the advice from a leading researcher at The University of Western Ontario who found surprising results in a study looking at the effects of vitamin B therapy on diabetic nephropathy. The study is published in the April 28 edition of the Journal of the American Medical Association (JAMA).

Diabetic nephropathy is kidney disease or damage that is a complication of diabetes. 21 million Americans and more than three million Canadians have diabetes, and over 40% of people with diabetes will develop nephropathy.

Dr David Spence of Western's Robarts Research Institute and his colleagues began their study of people with kidney disease, anticipating that people who received high dose vitamin B therapy (folic acid, vitamin B6 and vitamin B12) could see improved kidney function and fewer heart attacks and stroke, compared with those on placebos.

The opposite was true. Those receiving high dose vitamin B therapy had significantly greater worsening of kidney function, measured as GFR. GFR (glomerular filtration rate) is the test used to measure the level of kidney function. They also had twice as many heart and stroke incidents.

One predicted outcome did pan out. Homocysteine levels in those on vitamin B therapy were lowered. Homocysteine is an amino acid that increases clotting of the blood. Studies have shown that too much homocysteine in the blood is related to a higher risk of coronary heart disease, stroke and peripheral vascular disease.

The research was conducted at five university medical centres by Spence and his colleagues in the Department of Medicine at Western's Schulich School of Medicine and Dentistry, Dr Andrew House and Dr George Dresser, and by researchers at the University of Calgary, University of Toronto, McMaster University and the University of Manitoba.

'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 affects we have seen in this study,' says Spence. '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.' This means we will need to explore other approaches to lowering homocysteine in patients with kidney failure.