Should recommendations be made to reduce dietary sodium intake? The case against recommendations.

We are here to consider whether the evidence of benefit from reducing dietary sodium in hypertensive patients or in the population at large is sufficient to justify recommendation to the general public that dietary Na is reduced. I shall concentrate on four questions. First, and most important, when reduction of dietary Na lowers blood pressure will the risks associated with high blood pressure be reversed? Clearly it is pointless lowering blood pressure if the risks are not reversed. Indeed, there are circumstances in which it is known that lowering blood pressure in hypertension does not reverse risks associated with high blood pressure. Second, also important, but I believe less relevant to the debate, is dietary Na involved in the pathogenesis of hypertension? It does not matter so far as recommendations are concerned if Na is or is not involved in pathogenesis provided reduction of dietary Na lowers blood pressure and this reduces the risks associated with high blood pressure. Third, does reduction of dietary Na within the range one can expect to achieve in a general population lower blood pressure in hypertensive and normal individuals? Fourth, and finally, how feasible is it to reduce dietary Na? It was claimed recently in a review of three prospective randomized control trials (which we shall consider later) that practical Na restriction lowered blood pressure by 8 mmHg and that such a decrease would lower cardiovascular mortality by 10-15%. This optimistic prediction is based on a false premise. It is true that Na restriction did lower blood pressure by 8 mmHg in these trials, but the patients were hypertensive. The figure of 10-15% was taken from a different study, not concerned with hypertensive patients, and had no information on the effect of reducing blood pressure. Indeed, there is no evidence in normal or hypertensive subjects that a reduction of this order by any treatment would lower mortality. In particular, I know of no evidence that risk is reduced by dietary Na deprivation. In our own experience of treatment in hypertensive patients using drugs, a reduction of blood pressure lowered risk but not to the level found in the general population, even when blood pressure was reduced to that of the general population (Isles et al. 1986). Most of the evidence in favour of recommendations on dietary salt intake comes from epidemiology. A wide range of populations has k n studied, from primitive societies with an individual daily intake of 10 mmol Na to industrial societies with intakes twenty times higher than this. There is without doubt a reaeonably good relation between average blood pressure of these populations and their average