The INTERSALT study: an addition to the evidence on salt and blood pressure, and some implications.

The balance of evidence from animal studies, clinical observations, human experimental studies, and epidemiological studies favours a causal association between sodium and blood pressure. INTERSALT is the largest and most comprehensive study yet published on the sodium-blood pressure relationship, and its significant findings in individuals gives further support to a judgment of causality, although it is likely that the size of the relationship is underestimated. Trials of sodium restriction in individuals have generally shown an effect on blood pressure similar to that predicted from population studies. The effect seems to be more marked at older ages, at higher blood pressures and with more severe sodium restriction. In treated hypertensive patients, sodium restriction (either alone or in combination with weight loss and moderation of alcohol intake) can reduce the amount of medication required to control blood pressure, and in some cases blood pressure may be controlled by dietary measures alone, particularly in those whose hypertension is 'mild' (i.e., uncomplicated and with less marked elevations of pressure). The Portuguese salt trial showed that intervention at the community level can be successful in lowering both sodium intake and blood pressure, although this was not achieved in a community trial in Belgium. In the light of the evidence on sodium and blood pressure, recommendations on sodium intake are made with respect both to the individual, and to the population as a whole.