If you're confused by competing media reports on salt's safety, you're not alone. Investigations into the health effects of salt are as polarized as the water molecules that dissolve sodium chloride. An analysis of 269 reports on the topic shows we're a very long way from settling the question of whether salt is a health risk for most of the population.
There is general agreement that some people badly need to reduce their salt intake, or risk dangerously raised blood pressure. What remains in dispute, however, is whether this is also true for the population as a whole. Bodies as august as the World Health Organization (WHO) and the U.S. National Academies of Science have taken contradictory positions. Some consider low salt intake to be a concern of its own.
Little progress seems to have been made in resolving this question. In the International Journal of Epidemiology a team of researchers including doctoral student David Johns of Columbia University examined findings on the topic, including primary studies and systemic reviews, along with clinical guidelines and statements by medical groups.
Johns went back to 1979 for these, but more than half were published after 2011, indicating a rising interest in the topic. Moreover, while a majority supported the theory that high salt intake is a menace for all of us, this was a hardly overwhelming 54 percent. On the other hand, 33 percent concluded only a minority of us need to moderate our salt intake. Thirteen percent produced inconclusive results.
The disturbing aspect is that the two opposing groups were failing to engage with each other, instead behaving like two populations on social media that share statements and memes they agree with, barely even hearing the other side. “Reports were 1.51 times more likely to cite reports that drew a similar conclusion, than to cite reports drawing a different conclusion,” the paper notes, despite the potential for citations to be used to criticize as well as endorse. Only some of this could be explained through researchers preferentially citing their own work or that of coauthors.
Probably don't eat this much. Kasikun_Kamol/Shutterstock
"There are two almost distinct bodies of scholarship – one supporting and one opposing the claim that salt reduction in populations will improve clinical outcomes," Johns said in a statement. "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.'"
“Although science has been acutely alert to potential financial conflicts of interest in recent decades, much less attention has been paid to other potential conflicts – particularly biases that are embedded in long-held beliefs,” the paper observes.
The study may encourage the two sides of this debate to engage with each others' evidence. Moreover, Johns and his coauthors wrote, “To our knowledge, our analytical approach is novel as it allows an empirical quantification of such polarization.” They suggested their method may prove useful for studies of other areas where scientists continue to disagree, such as on the harms and benefits of electronic cigarettes.