The INTERSALT study: background, methods and main results. INTERSALT Co-operative Research Group

The INTERSALT study used standardised methods to assess the relations of electrolyte intake and blood pressure, taking account of confounding variables, in samples of men and women aged 20-59 drawn from defined populations in 52 centres and 32 countries (10,079 individuals). Sodium excretion was significantly related to blood pressure in individuals. Corrected estimates (probably still too low) indicated, on multiple regression, that a difference of 100 mmol/day in average population sodium intake corresponded to 2.2 mmHg lower systolic pressure. Sodium excretion across centres, with median levels ranging from 0.2 to 242 mmol/24 hour, was related to slope of blood pressure with age, less consistently to median centre pressure. Estimates indicated that a 100 mmol/day lower sodium intake was associated with a 9 mmHg lower rise of systolic pressure between ages 25 and 55. Hypertension was virtually absent in four populations with very low sodium intake, and blood pressure in these samples was not higher at older ages. Potassium intake of individuals was negatively and significantly associated with blood pressure independently of other variables; body mass index and high alcohol intake were strongly positively and independently associated with blood pressure in individuals.