Low Urinary Sodium Is Associated With Greater Risk of Myocardial Infarction Among Treated Hypertensive Men

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Abstract
A sodium-reduced diet is frequently recommended for hypertensive individuals. To determine the relationship of sodium intake to subsequent cardiovascular disease, we assessed the experience of participants in a worksite-based cohort of hypertensive subjects. The 24-hour urinary excretion of sodium (U Na V), potassium, creatinine, and plasma renin activity was measured in 2937 mildly and moderately hypertensive subjects who were unmedicated for at least 3-4 weeks. Morbidity and mortality in these systematically treated subjects were ascertained. Men and women were stratified according to sex-specific quartiles of U Na V. Subjects in these strata were similar in race, cardiovascular status, and pretreatment and intreatment blood pressure. Subjects with lower U Na V were thinner, excreted less potassium, and had higher plasma renin activity. During an average 3.8 years of follow-up, a total of 55 myocardial infarctions occurred. Myocardial infarction and U Na V were inversely associated in the total population and in men but not in women, who sustained only nine events. In men, age- and race-adjusted myocardial infarction incidence in the lowest versus highest U Na V quartile was 11.5 versus 2.5 (relative risk, 4.3, 95% confidence interval, 1.7-10.6). No association was observed between non–cardiovascular disease mortality (n=11) and U Na V. There was a significant linear trend in proportions of myocardial infarction by U Na V quartile, with a break point after the lowest U Na V quartile. In the Cox multivariate analysis, log plasma renin activity, age, systolic pressure, and cholesterol as continuous variables as well as left ventricular hypertrophy and smoking had a direct association, and U Na V ( P =.036) had an inverse, independent association with the incidence of myocardial infarction among these treated hypertensive men.