Dietary sodium and arterial pressure: problems of studies within a single population.

The nature of the relationship between dietary sodium and arterial pressure remains uncertain, largely because of the difficulty of investigating this relationship within a single population. There are two main hypotheses: one requires that hypertensive and normotensive patients differ in their sodium intake, the other that they differ in their susceptibility to dietary sodium. Neither hypothesis has been fully explored. In this paper the types of study required to test each hypothesis are considered and published work is used to illustrate the problems of interpreting studies in this field.