High-dose vitamin B worsens nephropathy, increases vascular events
FOCUS ON DIABETES CARE Charles D. Ponte, Section Advisor
High-dose vitamin B worsens nephropathy, increases vascular events
Key point: Results from a randomized, controlled trial of 238 patients with diabetes and nephropathy indicated that daily vitamin B supplementation with folic acid, vitamin B6, and vitamin B12 decreased plasma homocysteine levels but also decreased the glomerular filtration rate (GFR) and increased vascular events compared with placebo.
Finer points: The DIVINe (Diabetic Intervention with Vitamins to Improve Nephropathy) trial was conducted at five university medical centers in Canada to determine whether supplementation with folic acid 2.5 mg, vitamin B6 25 mg, and vitamin B12 1 mg daily slowed the progression of diabetic nephropathy and prevented vascular complications associated with elevated homocysteine levels. Patients with type 1 or type 2 diabetes and diabetic nephropathy were given a vitamin B supplement (n = 119) or placebo (n = 119) daily. Change in GFR and homocysteine levels, initiation of dialysis, and a composite vascular outcome that included myocardial infarction, stroke, revascularization, and all-cause mortality were assessed at 36 months. Total plasma homocysteine levels decreased by 2.2 ± 0.4 µg/L in patients receiving vitamin B supplementation, while the levels of those taking placebo increased by 2.6 ± 2.6 µg/L (mean difference –4.8 µg/L [95% CI –6.1 to –3.7], P < 0.001). GFR decreased in both groups; however, the decrease was greater in patients receiving vitamin B supplementation (mean difference –5.8 mL/min/1.73 m2 [–10.6 to –1.1], P = 0.02]). Dialysis did not differ between groups, with 10 patients in each group requiring dialysis by the end of the study. Although the number of events was small for each outcome, patients receiving vitamin B supplementation had twice the number of vascular events of those receiving placebo. The risk of experiencing an event in the composite outcome was 23.5% with vitamin B supplementation and 14.4% with placebo. No differences were observed in glycosylated hemoglobin concentrations or blood pressure measurements.
What you need to know: Even with currently available therapies, about 8.4 million Americans with diabetes develop nephropathy. High homocysteine levels have been associated with an increased risk of developing diabetic nephropathy, retinopathy, and vascular disease. B vitamins have been shown to reduce homocysteine levels. Most studies with large sample sizes failed to show that reducing homocysteine levels prevented stroke or MI. While some studies have suggested potential harm or neutral effects with vitamin B supplementation, DIVINe is the first study to demonstrate detrimental effects from vitamin B supplementation in this patient population. The study authors, Andrew House, MD, and colleagues, suggested that high levels of these B vitamins may be toxic to the renal, cardiovascular, and cerebrovascular systems and that these toxic effects offset any protective benefits that could have occurred with lowering homocysteine levels.
What your patients need to know: Tell patients with diabetes and nephropathy to avoid taking high doses of B vitamins as a means of lowering homocysteine levels. Explain that the benefits of taking these supplements have not been consis-tently reported and that potential harm to the kidneys and heart have been reported with use.
Sources: House AA et al. Effect of B-vitamin therapy on progression of diabetic nephropathy: a randomized controlled trial. JAMA. 2010;303:1603–9.
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