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A Call for Quality Research on Salt Intake and Health: From the World Hypertension League and Supporting Organizations

2014; Wiley; Volume: 16; Issue: 7 Linguagem: Inglês

10.1111/jch.12364

1751-7176

Norm R.C. Campbell, Larry J. Appel, Francesco P. Cappuccio, Ricardo Correa–Rotter, Graeme J. Hankey, Daniel T. Lackland, Graham A. MacGregor, Bruce Neal, Mark L. Niebylski, Jacqui Webster, Kevin Willis, Mark Woodward,

Renal function and acid-base balance

Extensive research supports the harmful effects of high dietary sodium.1-11 In several animal species, including chimpanzees, diets with added sodium result in increased blood pressure (BP), and, in all settings, sodium-induced hypertension is harmful.12 Further, in several animal models, increased dietary sodium directly causes inflammation and vascular, cardiac, and renal target organ damage independent of BP.13, 1 Increased dietary sodium is a procarcinogen for gastric cancer in animal studies and a probable procarcinogen in humans, as shown in epidemiological studies that have found close associations between sodium intake and gastric cancer.14, 15 Reducing dietary sodium decreases BP in adults and children,1 with a linear relationship down to the lowest levels of sodium intake tested in randomized controlled trials (about 1200 mg/d of sodium). Increased dietary sodium is also associated with increased vascular events in healthy populations and was estimated to cause more than 3 million sodium-related deaths in 2010 (http://viz.healthmetricsandevaluation.org/gbd-compare/). Reducing dietary sodium is projected to be one of the most effective (and cost-effective) interventions to improve health.16 Major health and scientific organizations around the world have recommended that dietary sodium levels be reduced.2-9, 17-30 Nevertheless, there are several studies which report that reducing dietary sodium is not beneficial while others have produced results suggesting harm.22 These studies have created substantive controversy and have drawn significant criticism from the scientific community for weaknesses in research design and methods, misinterpretation of study results, and potential conflicts of interest of the authors (Table 1).31-36 The Institute of Medicine commented that weak research design was a major factor in its inability to determine whether reduced sodium intake in the range of 1500 mg/d to 2300 mg/d was beneficial or harmful in reducing cardiovascular disease.22 A systematic review of the epidemiological literature examining methodological issues in cohort studies that relate sodium intake to outcomes found that nearly all studies had major methodological issues that could impact the direction of the relationship between sodium intake and outcomes or bias towards the null hypothesis.34 Rigorous research study design and conduct is needed to identify whether reducing dietary sodium is harmful or beneficial. The publication of further studies with weak designs and methods is likely to produce misleading and inconsistent results that will generate further controversy and confusion. Because controversy sells, such studies often attract unwarranted media attention, which undermines the public health message and casts doubt on solid evidence-based results. For these reasons, the World Hypertension League and supporting organizations (Table 2) make an urgent call for the setting of standards for research examining sodium intake and health. Such standards need to be considered by researchers in designing studies, by funding bodies, and by journal editors and reviewers. To ensure consensus and the use of best available evidence in setting the standards, the standards setting process should be aided by systematic reviews of the evidence and overseen by respected international and national health and scientific organizations. To this end, the World Hypertension League is now actively creating a working group dedicated to establishing these standards and expects this effort to be under way before the end of 2014. Drs Campbell, Appel, Correa-Rotter, Hankey, Lackland, MacGregor, Neal, Webster, Willis, and Woodward report no specific funding in relation to this research and no conflicts of interest to declare. Dr Cappuccio is an unpaid advisor to the World Health Organization; unpaid member of Consensus Action on Salt and Health, World Action on Salt and Health, and the UK Health Forum; and unpaid Trustee of the charity Student Heart Health. Dr Niebylski is a paid contractor for the World Hypertension League but has no other conflicts. This call for research standards was developed with input from all of the organizations listed in Table 2.