Is salt detrimental to our health? A new analysis of scientific reports and comments on the health effects of a high-salt diet conducted by researchers from Columbia University reveals a polarized opinion - 54 percent supported the hypothesis that a reduction in salt intake is associated with better health, while 33 percent were not supportive and 13 percent were inconclusive.
The team examined 269 academic reports published between the years 1979 and 2014, which includes primary studies, meta-analyses, clinical guidelines, consensus statements, comments, letters and narrative reviews. Each study was then placed into one of two categories - for or against the link between reduced salt intake and lower rates of heart disease, stroke and death. Furthermore, more than half of the reports were published after 2011, pointing to an increased interest in the question.
One of the most interesting revelations of the study is the fact that papers on either side of the hypothesis tend to cite reports that draw similar conclusions, while ignoring reports drawing different conclusions. Among the literature, there are a select few influential papers on each side of the argument that are commonly cited by supporters.
"There are two almost distinct bodies of scholarship--one supporting and one opposing the claim that salt reduction in populations will improve clinical outcomes," David Johns, who participated in the analysis, said in a press release. "Each is driven by a few prolific authors who tend to cite other researchers who share their point of view, with little apparent collaboration between the two 'sides.'"
"We pay quite a bit of attention to financial bias in our work," added Sandro Galea, who also participated in the analysis. "We seldom pay attention, however, to how long-held beliefs bias the questions we ask and the results we publish, even as new data become available."
Supporting this claim is the fact that an analysis of systemic reviews found little consistency in the primary study selections - if a primary study was chosen by a review, the chance that another study would select the same study was less than a third, shedding light on the uncertainty and disagreement as to what should be considered evidence in the field. Additionally, the choices that determined the studies to cite as primary influences were found to have a direct impact on the conclusions of systematic reviews.
"Decision-makers often must choose a course of action in the face of conflicting, uncertain evidence," said Ludovic Trinquart, co-author of the analysis. "Both the misuse of uncertainty and the exaggeration of certainty can shape the outcomes of public health decision-making processes."
The findings were published in the Feb. 17 issue of the International Journal of Epidemiology.
