Study: B vitamin therapy no help after MI.(Clinical Rounds)

STOCKHOLM -- Lowering plasma homocysteine with B vitamin therapy does not prevent subsequent MIs and strokes in patients who have had an MI--to the contrary, it may even be harmful, according to the results of the first large randomized treatment trial to examine the issue.

"The homocysteine hypothesis is dead. Homocysteine is not a causal risk factor. It is an innocent bystander," Kaare Harald Bonaa, M.D., told this newspaper at the annual congress of the European Society of Cardiology.

Homocysteine's relationship to cardiovascular disease has been a topic of intense investigation in the past decade. The homocysteine story would now appear to illustrate the hazards of extrapolating from epidemiologic association to clinical practice in the absence of favorable treatment outcome studies.

On the strength of considerable epidemiologic evidence linking high plasma homocysteine to increased MI and stroke rates, many American and European physicians have in recent years suggested B vitamin therapy to reduce homocysteine levels in their patients at high cardiovascular risk.

The rationale was that since such therapy was inexpensive, was thought safe, and could have turned out to have a big payoff in reduced clinical events, it might have been a reasonable strategy to use while awaiting results of randomized treatment outcome studies.

But now the Norwegian Vitamin Trial (NORVIT) has shown that such therapy does not prevent cardiovascular events; indeed, it may even increase the risk. And there was also a disturbing trend, albeit not statistically significant, for an increase in cancer, said Dr. Bonaa, professor of cardiology at the University of Troms[empty set] (Norway).

Dr. Bonaa was the principal investigator in NORVIT, a randomized, double-blind, multicenter trial in which 3,749 Norwegian patients were followed for 3.5 years after assignment to 0.8 mg/day of folic acid; 40 mg/day of vitamin [B.sub.6]; both; or placebo during their hospitalization for an acute MI. Participants also received all of the standard drugs given post MI.