LOW URINARY SODIUM IS ASSOCIATED WITH GREATER RISK OF MYOCARDIAL-INFARCTION AMONG TREATED HYPERTENSIVE MEN

3A 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 (UNaV), 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 UNaV. Subjects in these strata were similar in race, cardiovascular status, and pretreatment and intreatment blood pressure. Subjects with lower UNaV 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 UNaV 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 myocarcdial infarction incidence in the lowest versus highest UNaV 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 UNaV. There was a significant linear trend in proportions of myocardial infarction by UNaV quartile, with a break point after the lowest UNaV 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 UNaV (P=.036) had an inverse, independent association with the incidence of myocardial infarction among these treated hypertensive men.