Only Negligible Evidence Exists That Salt Raises Blood Pressure

The evidence for any health benefits associated with salt reduction is controversial and the "concealment of scientific uncertainty" is a mistake, claims a new study.

Researchers at Columbia University (New York, NY, USA) explored the development of the scientific controversy over the quality of the evidence implicating dietary salt in disease, which goes back to the early part of the 20th century. The researchers noted that most of the evidence pointed to the weakest of correlations between salt and blood pressure. Despite this, the cause to reduce salt was taken up rapidly by public health leaders at local, national, and international levels that pressed the case for salt reduction at the population level.

The researchers cited several studies that could not find a link between salt intake and elevated blood pressure. Examples of such studies include the 1967 study of the Framingham cohort, and Japanese and Scottish reports in the 1980s totaling 15,000 people that concluded the association between sodium and blood pressure is extremely weak. Another example is a 2011 Cochrane Review study that examined more than 150 randomized controlled trials and 13 population studies, which concluded, “Without an obvious signal in favor of sodium reduction, another position could be to accept that such a signal may not exist.”

Such studies usually face fierce opposition or even ridicule among peers. For example, in May 2011, the Journal of the American Medical Association (JAMA) published a study by Katarzyna Stolarz-Skrzypek, MD, PhD, and colleagues that found only a weak correlation between salt and blood pressure. A subsequent editorial in the Lancet criticized the JAMA study as likely to confuse public perceptions of the importance of salt as a risk factor for high blood pressure, heart disease, and stroke. The authors cited many more studies finding little association between salt and blood pressure that did not eliminate the stigma attached to the mineral.

“Science must remain open, skeptical, and concerned about unmeasured confounding and selection bias in studies that accompany even the best efforts to articulate the evidence for new interventions,” concluded lead author Ronald Bayer, PhD, and colleagues of the school of public health. “The concealment of scientific uncertainty is a mistake that serves neither the ends of science nor good policy. Simplistic pictures of translation from evidence to action distort our ability to understand how policy is, in fact, made and how it should be made.”

The researchers noted that in the 1990s, C. Everett Koop, MD, the then US Surgeon General, issued a report noting that government agencies were “very quick to embrace the importance of salt reduction in the 1970s and 1980s, which stood in stark contrast for the snail's pace of recommendations related to reducing blood cholesterol levels.”

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