The intersalt study: background, methods, findings, and implications

The INTERSALT Study is a standardized, worldwide epidemiologic study of large sample size (n = 10079 men and women ged 20-59 y from 32 countries) that tested both within- and cross-population prior hypotheses on 24-h sodium excretion and blood pressure. For individuals, a significant, positive, independent linear relation between 24-h sodium excretion and systolic blood pressure (SBP) was found. With multivariate adjustment for underestimation, the estimated effect of a sodium intake higher by 100 mmol/d was higher SBP/DBP (diastolic blood pressure) by approximately 3-6/0-3 mm Hg. This relation prevailed for both men and women, for younger and older people, and for 8344 people without hypertension. In tests of prior cross-population hypotheses (n = 52), significant, independent relations were found between sample 24-h median urinary sodium excretion and sample median SBP and DBP, prevalence rate of hypertension, and slope of SBP and DBP from age 20 to 59 y (median sodium intake greater by 100 mmol/d was associated with a 30-y increase in SBP/DBP, i.e., at the age of 55 y compared with 25 y, of 10-11/6 mm Hg. The INTERSALT results, which agree with findings from other diverse studies, including data from clinical observations, therapeutic interventions, randomized controlled trials, animal experiments, physiologic investigations, evolutionary biology research, anthropologic research, and epidemiologic studies, support the judgment that habitual high salt intake is one of the quantitatively important, preventable mass exposures causing the unfavorable population-wide blood pressure pattern that is a major risk factor for epidemic cardiovascular disease.