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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:
Posted by Alex Egervary (aegervary@aphanet.org)
July 16, 2010, 3:00 pm
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