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

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 (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 myocardial 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Salt reduction and cardiovascular risk: the anatomy of a myth

“…This did not prevent Alderman and colleagues drawing attention to the similarity of their conclusions to those they had come to in their previous paper. They commented that: 'The inverse association of salt intake with mortality is consistent with the findings of a similar observational study 7 of 3000 participants in a systematic programme to control hypertension'. In other words in spite of the misrepresentations and faulty urinary sodium excretion estimations in their first paper, and the defective data in their second, Alderman and colleagues wished it to be known that they still subscribe to the myth that a low salt intake is dangerous.…”

“…In the past 3 years Alderman and colleagues have published two papers which they believe to show that an habitual reduction in salt intake in humans increases the risk of myocardial infarction. 7,8 I believe that this assertion is not supported by the published evidence. The first paper claimed that among a group of 3000 patients with hypertension, 'baseline' 24 h urinary sodium excretion was inversely related to subsequent myocardial infarction and cardiovascular disease and that therefore the habitual consumption of a low salt intake increases the incidence of myocardial infarction'.…”

Effect of modest salt reduction on blood pressure: a meta-analysis of randomized trials. Implications for public health

“…Alderman et al have attempted to look at the effect of salt intake on cardiovascular disease in two cohort studies, one is a follow-up study of a worksite screening project in New York, 46 and the other involved the NHANES 1Fa dietary survey of US adults from the mid 1970s. 47 They suggested that a low salt diet might increase the risk of cardiovascular disease.…”

Salt reduction and cardiovascular risk

“…2 Since epidemiology is about associations, alternate explanations for the observed facts must always be explored. The scenario Professor de Wardener proposed must be tested for compatibility with the information in the original published article.…”

“…The relevant published data, to our knowledge, is limited to three prospective observational studies. 2,4,5 They provide no evidence that a low sodium intake is beneficial, nor that a high sodium intake is harmful. Indeed, two of these three studies raise concerns about the safety of a low sodium intake.…”