Salt—overwhelming evidence but still no action: can a consensus be reached with the food industry?BMJ 1996; 312 doi: http://dx.doi.org/10.1136/bmj.312.7041.1287 (Published 18 May 1996) Cite this as: BMJ 1996;312:1287
- Graham A MacGregor, professor of cardiovascular medicinea,
- a Blood Pressure Unit, St George's Hospital Medical School, London SW17 0RE
- b Imperial College School of Medicine at St Mary's, London W2 7PG
- Correspondence to: Professor MacGregor.
Evidence that our current high salt intake plays an important role in blood pressure regulation comes from many sources, chiefly epidemiological studies, intervention studies, migration studies, studies of salt restriction, and evidence in mammals.
Epidemiological studies illustrate that salt intake may be a major factor in determining differences in blood pressure between and within communities as well as being closely associated with the rise in blood pressure with age in communities with a high salt intake. But these studies can only suggest relationships. Attempts to derive from epidemiological evidence simple relationships between a rather crude index of sodium intake and blood pressure will inevitably be confounded by the variable expression of other environmental and genetic factors, which may modulate the blood pressure response to sodium.1 Further analyses of results from large epidemiological studies such as Intersalt are unlikely to shed further light on this complex issue. It is therefore necessary to look at different types of evidence that more clearly show the effect of salt on blood pressure.
Stronger evidence comes from intervention studies such as a carefully controlled six month double blind study in newborn babies.2 Those receiving a modestly restricted salt intake had a significantly lower blood pressure (2.1 mm Hg) than those with a normal sodium intake. As the sodium restriction was discontinued at six months it is not known whether this difference would have increased, but a reduction of even 2.0 mm Hg in population blood pressure would have immense benefits in reducing cardiovascular morbidity and mortality. In another study, a village in Portugal reduced salt intake by reducing salt in cooking and also in processed food, including bread. At the end of the observation period blood pressure was significantly lower than in a control …
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