Relevance of the salt-hypertension hypothesis to the community control of hypertension.

By applying the Framingham data to the distribution of blood pressure in the Australian population, it can be shown that almost half the morbidity from strokes and ischaemic heart disease that is attributable to blood pressure would be expected to occur in subjects who are "normotensive" by the current World Health Organization (WHO) definition. The steadily increasing risk with every increment of diastolic blood pressure above 70 mmHg supports the contention that the dividing line between "normotension" and "hypertension" is artefactual, and that the basic problem is the tendency for blood pressure levels to rise with age. The rise with age occurs exclusively and invariably in salt-eating societies, and the most promising hypothesis that is awaiting evaluation is that this rise could largely be prevented by the universal adoption of the Australian Recommended Dietary Intake for sodium of 40-100 mmol/day. Two factors that may limit the prophylactic effect of avoiding salt are self-sustaining hypertension and teratogenic hypertension, both of which are seen when rats are fed salt. In Australia and several other countries it is already official policy to recommend a lower intake of salt. Although we support this, we consider that interventions with such massive implications are incomplete without a serious attempt to measure the outcome. Double-blind conditions would be impossible, but a large-scale population-based trial with randomization would be feasible. The first stage of the trial should consist of a campaign of salt reduction in patients with established hypertension, in collaboration with medical practitioners and the food industry, because it is unrealistic to expect good dietary compliance from several thousand "normotensive" persons until those who want to avoid salt are catered for more adequately.