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Salt, science and politics

Journal of Human Hypertension volume 17, pages 1–3 (2003)Cite this article

In the first decade of the 19th century, Ambard and Beaujard demonstrated a connection between salt intake and high blood pressure in a small but carefully conducted feeding experiment (cited by MacGregor).1 One hundred years later, the hypo-thesis that salt intake plays a causal role in the rise in blood pressure with age and the development of essential hypertension continues to generate controversy.2,3,4,5,6,7 Recommendations advocating a modest reduction in salt intake in developed countries from current levels of around 10 g/day to 5 g/day (an intake well in excess of physiological requirements) are vehemently contested. The intensity of this debate is signalled by the number of meta-analyses of randomised controlled trials addressing the effects of sodium restriction on blood pressure, at least five to date.7,8,9,10,11 Feng and MacGregor have stirred the pot with a further meta-analysis in a recent issue of the Journal of Human Hypertension.12

MacGregor's group are robust proponents of the argument linking salt with essential hypertension and other adverse outcomes based on a substantial contribution to the literature over two decades.13 Unfortunately, such is the intensity of the ‘salt wars’ that some will dismiss this paper as a partisan contribution, a further effort to create the ‘appearance of scientific unanimity’.4 However, I believe that most reasonable observers will accept that this meta-analysis, based on 17 trials of modest reductions in salt intake in hypertensives and 11 similar trials in normotensives, represents an important contribution to the literature. The case for excluding from the meta-analyses both trials of very short duration (1 week or less) and acute salt loading and salt depletion experiments is unanswerable. The latter trials and experiments may well be relevant to clarifying physiological mechanisms, but they provide a limited basis for causal inference and the development of public health policy recommendations. The findings from this meta-analysis are consistent with those of Law et al7 and Cutler et al8,10 reported in the last decade. The median reduction in salt intake in the trials was approximately 5 g/day, and this was associated with an average fall in blood pressure of 4.96/2.73 mmHg in hypertensives and 2.03/0.97 mmHg in normo-tensives. In weighted linear regression analyses, a reduction of 100 mmol/day (6 g) in salt intake predicted a fall in blood pressure of 7.1/3.9 mmHg in hypertensives and 3.6/1.6 mmHg in normotensives. These effects are substantial in population health terms and are consistent with the hypothesis that a relatively modest reduction in average dietary salt intake at the population level is likely to produce substantial falls in stroke and coronary heart disease mortality.

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  1. Department of Epidemiology and Public Health, University College Cork, Cork, Ireland

    I J Perry

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Perry, I. Salt, science and politics. J Hum Hypertens 17, 1–3 (2003). https://doi.org/10.1038/sj.jhh.1001500

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