Kidney disease and B vitamin therapy: Concern or Controversy?

Can too much of a water soluble vitamin really be bad for your kidneys? I first ran across an article “B Vitamins Harm Kidneys” in the June issue of Nutrition Action Healthletter (http://www.cspinet.org/). According to the article about a Canadian research study, 238 diabetics with early stage chronic kidney disease (CKD) took a high dose folic acid, vitamin B-6, vitamin B-12 pill or a placebo. After three years the study revealed a greater decrease in kidney function and heart attack or stroke in the participants receiving the B vitamin.

I read another article on the same research study in the June issue of Nephrology News and Issues http://www.nephronline.com/ titled “High vitamin B doses may accelerate kidney damage”. The original research was published in the Journal of the American Medical Association (JAMA), April 2010. One of the Diabetic Intervention with Vitamins to Improve Nephropathy (DIVINe) study goals was to determine if the high doses of B vitamins decreased levels of the amino acid metabolite, homocysteine. High homocysteine is linked to a greater risk of heart disease and stroke, even in the normal population. Results were a decrease in homocysteine levels with B-vitamin therapy, but unexpectedly, an increase in stroke and cardiovascular events. However, the number of patients who required dialysis during the three year study period was equal–ten from the vitamin group and ten from the placebo group.

Yet another article on this research study, “B-Vitamin Therapy Linked to Increased Risk in Small Diabetic Nephropathy Trial, but Results Controversial” was published in the May 2010 issue of Nephrology Times www.nephrologytimes.com. Experts questioned several aspects of the study: a small number or participants, borderline significant results, and the fact that larger studies have not shown the harmful effects from even higher doses of B vitamins. One study cited, Homocysteinemia and End-Stage Renal Disease (HOST) had over 2000 participants with advanced kidney disease and did not show evidence that even higher doses of the B vitamins are harmful. One question that was brought up—Is there something about having diabetes and CKD that causes harmful effects in this group? or did study participants who had cardiovascular events have a reduction in kidney function due to the cardiovascular event rather than harm from the vitamins? More analysis of the study data may help provide answers.

In the mean time, what’s safe for you if you have diabetes and CKD? It’s known that changing from a regular healthy diet to a kidney diet may cause lower intake of folic acid, vitamin B-6 and vitamin B-12. In addition, when CKD patients start dialysis there is a loss of B-vitamins from the blood during dialysis.  Deficiency of any of these B vitamins can cause anemia, as well as nerve and skin abnormalities. The chart below compares two of the above mentioned research study B-vitamin levels with a typical renal vitamin and a regular multivitamin.

From a dietitian point of view, try to eat a healthy diet and get your vitamins from food sources. If you have early stage kidney disease, consider a multivitamin if your diet changes have resulted in a decreased intake of meats, milk, whole grains, nuts, dried beans, fruits and vegetables. If you are in later stage kidney disease or on dialysis, stick with the renal vitamin prescribed by your kidney doctor, since the many dietary restrictions contribute to inadequate B vitamin intake and dialysis causes increased losses. If you are taking a vitamin with very large doses of folic acid, B-6 or B-12, ask your doctor about the benefits versus harm.

Kidney diet resources from DaVita.com

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