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BMJ 2010; 340 doi: (Published 04 May 2010) Cite this as: BMJ 2010;340:c2370

Time to rethink B vitamins for lowering homocysteine

Supplements of B vitamins that include folic acid reduce serum concentrations of homocysteine but seem to make little to difference to important vascular outcomes, such as heart attacks and strokes. A Canadian trial now reports that high doses may be positively harmful. Adults with diabetic nephropathy given a supplement containing folic acid (2.5 mg/day), vitamin B-6 (25 mg/day), and vitamin B-12 (1 mg/day) developed significantly worse renal function over three years than controls given a placebo. The supplement accelerated declining glomerular filtration rates and was associated with significantly more vascular events including deaths (hazard ratio 2.0, 95% CI 1.0 to 4.0).

The authors weren’t expecting these results and can’t rule out vitamin toxicity. Their 238 participants were not short of B vitamins at the start of the trial, thanks in part to Canada’s policy of adding folic acid to many cereals. Poor renal excretion of these water soluble vitamins pushed concentrations even higher.

It may be time to abandon B vitamins as a way to reduce …

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