The general aim of INTERSALT has been , jointly in London and Chicago, to coordinate an international study on the relation between electrolyte excretion and blood pressure (BP).
Specific aims for the new grant period are to complete data and laboratory analyses and perpare additional manuscripts on findings for the 10,079 persons seen in 52 centers in 32 countries. Main hypotheses are: a) sodium (Na) intaked and BP are positively related, b) potassium (K) is negatively related to BP, anc c) Na/K is positively related to BP. While these hypotheses have been current for years, they have never been tested under a common protocol, with standardized measurement of BP, urinary electrolytes, and possible confounding variables. INTERSALT has conducted such an investigation systematically, following a joint Protocol and Manual of Operations, selecting random samples of 200 men and women age 20-59 in each country. Urine samples were analyzed for Na, K, Cl, Ca, Mg, and creatinine at the study's Central Laboratory in Belgium. Data, entered into the London central computer, were analyzed for the main study hypotheses. Overall, there was a positive relation of NA intake, body mass index, and high alcohol intake with BP, and a negative K-BP relation. Populations with very low Na had virtually no hypertension or rise of BP with age. This application is for partial support for further computer analyses of the wealth of INTERSALT data. Some factors to be studied, both for their independent relation to BP and their role in modifying the electrolyte-BP relation are: weight and height considered separately; urinary Ca and Mg; alcohol; age and sex; possible confounders such as ambient temperature, smoking, the pill, diet changes; social factors (education, etc.). Also to be studied are: intra-and inter-individual variability in electrolyte intake and BP, and effect on electrolyte-BP relationships, subgroups of similar populations (e.g., very low Na); methodologic isues (e.g., electrolytes in casual vs. 24-hr urines and BP; creatinine level as a measure of collection completeness). Partail support is also sought for analyses of 10,000+ frozen specimens for urea, sulfate, and taurine, factors reflecting protein intake and possibly related to BP and the electrolyte-BP association. Partial support to these INTERSALT activities over the next 3 years will permit extensive utilization of the large mass of scientific information already collected to advance knowledge on dietary aspects of the etiology of hypertension, a mass disease in most of the world's populations.
