Education And Debate

Commentary: Strength and importance of the relation of dietary salt to blood pressure

BMJ 1996; 312 doi: https://doi.org/10.1136/bmj.312.7047.1661 (Published 29 June 1996) Cite this as: BMJ 1996;312:1661
  1. Alan R Dyer, professor (adyer@nwu.edu)a,
  2. Paul Elliott, professorb,
  3. Michael Marmot, professorc,
  4. Hugo Kesteloot, professord,
  5. Rose Stamler, professor emeritusa,
  6. Jeremiah Stamler, professor emeritusa

    for the Intersalt Steering and Editorial Committee

  1. a Department of Preventive Medicine, Northwestern University Medical School, Chicago, IL 60611-4402, USA
  2. b Department of Epidemiology and Public Health, Imperial College School of Medicine at St Mary's, London W2 1PG
  3. c Department of Epidemiology and Public Health, University College London Medical School, London
  4. d Department of Epidemiology, St Raphael University Hospital, Leuven, Belgium
  1. Correspondence to: Professor Dyer

    Geoge Davey Smith and Andrew Phillips raise some issues concerning methods used in correcting for regression dilution in Intersalt but offer no judgment on the crucial issue of the strength and importance of the relation of dietary salt to blood pressure. To assess this matter properly, in the context of Intersalt findings, three judgments must be made: firstly, on the aetiological significance of the salt-blood pressure relation; secondly, on the probable underestimate of the size of this relation in Intersalt analyses of individuals; and thirdly, on the soundness of Intersalt's updated estimates “revisiting” the strength of this relation, both from its within population and its cross population analyses.1 Davey Smith and Phillips deal not at all with the first and second of these points, and only partially and inconsistently with the third. Much of their commentary deals with generalities, not with specifics of the salt-blood pressure relation and Intersalt results. As a consequence, their commentary neither sheds light on the substantive matter nor contributes positively to public policy.

    Aetiological significance of the dietary salt-blood pressure relation

    Davey Smith and Phillips state that corrections for regression dilution and other biases “could as well be applied to spurious associations as to causal ones…. Judgment has to be applied to decide if an association is causal.” They make no such judgment on the salt-blood pressure relation, the subject of their commentary. In fact, the totality of the evidence—the only sound basis for judgment on this matter—supports the conclusion that this association is causal. The significant independent findings on the sodium-blood pressure relation in Intersalt's within population and cross population analyses1 are components of that total evidence. Independent expert groups, national and international, have repeatedly concluded that the extensive, concordant, strong data from all disciplines—clinical investigation, randomised controlled trials, animal experimentation, epidemiological research …

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