May 20, 2016

expert reaction to global study on low salt diets

Publishing in The Lancet, a group of researchers have reported that high sodium intake is associated with an increased risk in cardiovascular events and death in hypertensive populations, but not in normotensive populations.

Victoria Taylor, Senior Dietician at the British Heart Foundation, said:

“This is an interesting observational study but more research is needed to confirm these findings before making changes to policies which advise the population on salt reductions.

“Although the method for measuring salt consumption in this study is robust, no other dietary information such as fruit and vegetable intake, was collected from participants. It’s important to take the full  diet into account as other factors, not just salt intake, could have affected blood pressure.

“This reinforces the need to take a whole diet approach to prevent cardiovascular disease, rather than focusing on single nutrients, foods or risk factors.”

Professor Francesco Cappuccio, Head of the World Health Organization Collaborating Centre for Nutrition and Cephalon Professor of Cardiovascular Medicine & Epidemiology University of Warwick, said:

“It is with disbelief that we should read such bad science published in The Lancet. The current paper contains a re-publication of data already presented using the PURE, ONTARGET and TRASCEND data ‘enriched’ by the EpiDREAM study.

“The flaws that were extensively noted in their previous accounts are maintained and criticisms ignored. They include a flawed assessment of salt intake by using early morning spot urine sodium concentrations extrapolated to 24h excretion using the inadequate Kawasaki equation, the critical problem of reverse causality whereby the participants are almost exclusively from clinical trials of sick people that have a very high risk of dying and are taking several medications.

“To these reiterated errors the authors add the statistical sin of splitting analyses of continuous variables (blood pressure) into groups of normotensive and hypertensive, a classification biologically meaningless, pretending to show that the effects vary between these groups. Similar analyses made by a Cochrane Review a few years ago were disproved and the review then retracted. By publishing studies with larger samples but with the same flaws the authors can only make their errors bigger.

“Whilst it is not surprising that none of the publications raising doubts on their previous findings are quoted in the reference lists, it is surprising that none of the reviewers, nor the Editors of The Lancet, have spotted these glaring omissions. The evidence supporting global actions for a moderate reduction in salt consumption to prevent cardiovascular disease is strong and such studies should not overturn the concerted public health action to reduce salt intake globally.”

* ‘Associations of urinary sodium excretion with cardiovascular events in individuals with and without hypertension: a pooled analysis of data from four studies’ by Andrew Mente et al., published in The Lancet  Friday 20th May.

Declared interests

Victoria Taylor: None Received

Professor Francesco Cappuccio:

Head, WHO Collaborating Centre

Advisor to World Health Organization

Member of CASH, WASH, UK National Forum

Vice-President, British Hypertension Society

Trustee, British Hypertension Society; Student Heart Health Trust

ALL UNPAID