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Letters

Too much focus on low-quality science?

Norm Campbell, Mary R. L’Abbe and Earle W. McHenry
CMAJ February 03, 2015 187 (2) 131-132; DOI: https://doi.org/10.1503/cmaj.115-0005
Norm Campbell
Departments of Medicine, Community Health Sciences, Physiology and Pharmacology (Campbell), Libin Cardiovascular Institute of Alberta, O’Brien Institute of Public Health, University of Calgary, Calgary, Alta.; Department of Nutritional Sciences (L’Abbe, McHenry), Faculty of Medicine, University of Toronto, Toronto, Ont.
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Mary R. L’Abbe
Departments of Medicine, Community Health Sciences, Physiology and Pharmacology (Campbell), Libin Cardiovascular Institute of Alberta, O’Brien Institute of Public Health, University of Calgary, Calgary, Alta.; Department of Nutritional Sciences (L’Abbe, McHenry), Faculty of Medicine, University of Toronto, Toronto, Ont.
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Earle W. McHenry
Departments of Medicine, Community Health Sciences, Physiology and Pharmacology (Campbell), Libin Cardiovascular Institute of Alberta, O’Brien Institute of Public Health, University of Calgary, Calgary, Alta.; Department of Nutritional Sciences (L’Abbe, McHenry), Faculty of Medicine, University of Toronto, Toronto, Ont.
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This article has a correction. Please see:

  • Forum - April 07, 2015

The controversy concerning dietary sodium results primarily from low-quality studies and their commercial marketing and promotion.1–5 Low-quality studies do not adequately assess sodium intake, they use extreme variation in dietary sodium and they measure outcomes over a duration of a few days. They do not address known confounding factors for the outcomes being tested nor do they control for blood pressure (the main mechanism of sodium-induced harm) and they are conducted in populations with diseases where reverse causality is likely. Such poor-quality studies are often promoted and occasionally conducted by consultants of the Salt Institute (an umbrella organization of the salt industry). The publication of such studies, leveraged by the private sector, has created a false aura of scientific controversy around dietary salt.1–5

Although the call for a large randomized controlled trial on dietary sodium is not new, it has limited feasibility in Western countries where the food supply contains so much sodium.6 In Africa, where some populations still have low sodium intake, it was deemed unethical to increase dietary sodium in a trial setting. In China, where sodium added during cooking is a major source of dietary sodium, a large randomized controlled trial with a salt substitute is underway, but results will be confounded by very high baseline sodium intake and the need to use a salt substitute with potassium (a beneficial nutrient). In other countries, extensive dietary advice and support, when used alone, has proven ineffective at substantially lowering dietary sodium over the long haul.7 Hence, a large trial based on advice alone is unlikely to lower sodium intake, let alone show changes in outcomes.

It is important to also consider the World Health Organization (WHO) forum and technical meeting, “Reducing salt intake in populations,” discussed by MacLeod and Cairns.8 The WHO forum was developed around controversial new evidence from the PURE study, which categorized an individual’s long-term sodium intake based on a single “spot” (fasted first morning) urine sample.9,10 This method is widely recognized as inadequate to assess a person’s usual sodium intake, would not meet the minimum study quality criteria of blood-pressure studies for inclusion in the WHO evidence review11,12 and is therefore unlikely to have a bearing on dietary sodium recommendations.13,14

It is concerning that the PURE validation study for using spot urine samples was fraught with methodologic issues that could inflate the perceived utility of such samples.5,9 The content and topics of the WHO forum were structured around several presenters with known conflicts of interest and close industry involvement. Although a “balance” of scientists representing public health and scientific organization views were later invited to the WHO forum, they were not asked to contribute to MacLeod and Cairns’ article.8

The conclusion that dietary sodium reduction is controversial was announced in WHO advertising before the forum program was even finalized, resulting in the withdrawal of several invited speakers. Organizers did not respond to a call for public disclosure on the distribution and use of industry funds raised. Commercial sponsorship by the food and beverage industry of food-policy meetings has been viewed as a public health threat.15

That a small group of dissident scientists, most of whom have conducted weak and flawed research, and a few scientists with long histories of working with food and salt industries disagree is not a surprise. That MacLeod and Cairns’8 article caters to this small conflicted group is a concern as it provides undeserved credence and endangers public health.

Footnotes

  • Competing interests: Norm Campbell is a member of World Action on Salt and Health, Co-chair of the Pan American Health Organization/World Health Organization Technical Advisory Group on Dietary Salt and the HSF CIHR Chair in Hypertension Prevention and Control and was on the steering committee of the Canadian Sodium Working Group. Norm Campbell received travel support in 2012 from Novartis to present on hypertension control. Mary L’Abbe has received funding for sodium research from the CIHR, CSN, HSFC, DFC and IDRC; she received funding (2014–2015) from the Retail Council of Canada to examine changes in sodium levels in the Canadian food supply. She was Chair/Vice-chair of the Canadian Sodium Working Group and is a member of the WHO Nutrition Guidance Expert Advisory Group on Diet and Health and the HSFC Compass advisory group.

References

  1. ↵
    1. Cobb LK,
    2. Anderson CA,
    3. Elliott P,
    4. et al
    . Methodological issues in cohort studies that relate sodium intake to cardiovascular disease outcomes: a science advisory from the American Heart Association. Circulation 2014;129:1173–86.
    OpenUrlAbstract/FREE Full Text
    1. Campbell NR,
    2. Lackland DT,
    3. MacGregor GA
    . Dietary sodium: a perspective on recent sodium evidence — its interpretation and controversies. J Clin Hypertens (Greenwich) 2013;15:765–8.
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    1. Neal B,
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    . An update on the salt wars — genuine controversy, poor science, or vested interest? Curr Hypertens Rep 2013;15:687–93.
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    2. Whelton PK
    . Flawed evidence should not derail sound policy: the case remains strong for population-wide sodium reduction. Am J Hypertens 2013;26:1183–6.
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    1. Campbell NRC,
    2. Lackland DT,
    3. Niebylski ML,
    4. et al
    . Is reducing dietary sodium controversial? Is it the conduct of studies with flawed research methods that is controversial? A perspective from the World Hypertension League Executive. J Clin Hypertens (Greenwich) 2014; Nov. 6 [Epub ahead of print].
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    1. Fischer PW,
    2. Vigneault M,
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    4. et al
    . Sodium food sources in the Canadian diet. Appl Physiol Nutr Metab 2009;34:884–92.
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    1. Hooper L,
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    3. Smith GD,
    4. et al
    . Systematic review of long term effects of advice to reduce dietary salt in adults. BMJ 2002;325:628–37.
    OpenUrlAbstract/FREE Full Text
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    1. MacLeod SM,
    2. Cairns J
    . Controversial sodium guidelines: Scientific solution or perpetual debate? CMAJ 2015;187:95–6.
    OpenUrlFREE Full Text
  6. ↵
    1. O’Donnell M,
    2. Mente A,
    3. Rangarajan S,
    4. et al
    . Urinary sodium and potassium excretion, mortality, and cardiovascular events. N Engl J Med 2014 ;371:612–23.
    OpenUrlCrossRefPubMed
  7. ↵
    1. Campbell N
    . Validation and comparision of three formulae to estimate sodium and potasium excretion from a single morning fasting urin compared to 24-h measures in 11 countries. J Hypertens 2014;32:2499–500.
    OpenUrlCrossRefPubMed
  8. ↵
    1. Aburto NJ,
    2. Ziolkovska A,
    3. Hooper L,
    4. et al
    . Effect of lower sodium intake on health: systematic review and meta-analyses. BMJ 2013;346:f1326.
    OpenUrlAbstract/FREE Full Text
  9. ↵
    WHO guideline: sodium intake for adults and children. Geneva (Switzerland): World Health Organization; 2012.
  10. ↵
    1. Campbell NR,
    2. Appel LJ,
    3. Cappuccio FP,
    4. et al
    . A call for quality research on salt intake and health: from the World Hypertension League and Supporting Organizations. J Clin Hypertens (Greenwich) 2014;16:469–71.
    OpenUrlPubMed
  11. ↵
    1. Ji C,
    2. Sykes L,
    3. Paul C,
    4. et al
    . Systematic review of studies comparing 24-hour and spot urine collections for estimating population salt intake. Rev Panam Salud Publica 2012;32:307–15.
    OpenUrlCrossRefPubMed
  12. ↵
    1. Freedhoff Y,
    2. Hebert PC
    . Partnerships between health organizations and the food industry risk derailing public health nutrition. CMAJ 2011;183:291–2.
    OpenUrlFREE Full Text
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Canadian Medical Association Journal: 187 (2)
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Vol. 187, Issue 2
3 Feb 2015
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Norm Campbell, Mary R. L’Abbe, Earle W. McHenry
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Too much focus on low-quality science?
Norm Campbell, Mary R. L’Abbe, Earle W. McHenry
CMAJ Feb 2015, 187 (2) 131-132; DOI: 10.1503/cmaj.115-0005
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