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May 12, 2004

Vitamin Supplementation and Risk of Stroke

Author Affiliations

Letters Section Editor: Stephen J. Lurie, MD, PhD, Senior Editor.

JAMA. 2004;291(18):2191-2192. doi:10.1001/jama.291.18.2191-b

To the Editor: Dr Toole and colleagues1 concluded that reduction of serum homocysteine levels had no effect on recurrent cerebral infarction, coronary heart disease, and death after 2 years of follow-up. As the authors acknowledged, the trial lacked statistical power to show the reduction in risk that would be expected from the observed changes in serum homocysteine levels. The average difference in serum homocysteine levels in the trial between the treated and control groups after 1 year was 2.2 µmol/L. It has been estimated2 that a 3-µmol/L reduction in serum homocysteine level is associated with a relative risk of stroke of 0.76 (95% confidence interval [CI], 0.67-0.85) and a relative risk of coronary heart disease events of 0.84 (95% CI, 0.80-0.89). Therefore, a 2.2-µmol/L difference in serum homocysteine levels would, over enough time, be expected to result in an 18% (95% CI, 11%-25%) reduction in risk of stroke and a 12% (95% CI, 8%-15%) reduction in the risk of coronary heart disease events. The trial found a 10% reduction in risk of coronary heart disease (relative risk, 0.9 [95% CI, 0.7-1.2]) but no decrease in stroke (relative risk, 1.0 [95% CI, 0.8-1.3]). The result for coronary heart disease is close to that expected from the reduction in serum homocysteine levels, and the result for stroke is within the expected 95% CIs. One cannot, therefore, conclude no effect of homocysteine reduction; the trial result is consistent both with no effect and with the expected effect.

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