How do we know what to believe when it comes to science? Some might look at that question and answer that science doesn’t require belief; the facts and the research should speak for themselves.
Unfortunately, if you’ve delved into the scientific literature, you know that “facts” are rarely as black and white as we’d like them to be, that science and facts often require interpretation, and that true consensus within any topic takes decades—sometimes centuries—and is preciously rare.
In the meantime, people are suffering and dying from illnesses that science, eventually, might show us how to prevent. It is understandable that those within the research community and those in public policy feel compelled to act—to “do something”—now with what we think we know today.
However, what we thought we knew often proves to be inaccurate. This may be what happened with the commonly-held belief that lower sodium diets are always healthy, as I detail in my new CEI study, “Shaking up the Conventional Wisdom on Salt: What Science Really Says about Sodium and Hypertension,” published this week.
If you ask 10 people on the street what they think about salt’s role in human health, more than eight out of 10 will likely give some variation of the “salt dogma”—they’ll reveal some level of belief in the idea that lowering sodium will reduce blood pressure and improve health. A year ago, I might have been among them. But, despite what many in the public health field would have us believe, this consensus is not shared by those within the research community. As a study published last year demonstrated, only about half of those in the field believe there is evidence to support population-wide sodium reduction (policy attempts to get us all to lower salt consumption).
In addition to the shakiness of the current dogma, the most shocking findings from my research were how polarized the experts are on this issue and why our fervent belief in the evils of sodium has stuck around for 40 years, despite ever-increasing evidence to the contrary.
The intense, vitriolic, and largely ideological war that has been raging over salt for more than a century can be broken out into two camps:
Camp 1 believes the science irrefutably shows higher sodium leads to higher blood pressure, and therefore getting the general population to lower consumption to the government-recommended limit would result in lower blood pressure and better health outcomes.
Camp 2 is skeptical that salt is the main driver of hypertension or that sodium restriction is the best way to improve health outcomes for broad swaths of the population.
Whenever anyone from Camp 2 publishes a study, members of Camp 1 invariably criticize the study, and vice versa. Accusations range from the typical “methodological flaws” argument to the more inflammatory “industry influence” charge. Often, claims are made that the preponderance of “good” evidence points strongly enough one way or the other that action is justified.
Wading into this gang war, I expected CEI’s study to receive criticism from one side or the other (if not both). And, lo and behold, the American Heart Association (AHA)—which advocates for an even lower level of sodium than even the government recommendation—was the first to come out against it. What was surprising and instructive was the study the AHA cited as evidence of the wisdom of population-wide sodium reduction.
The research, published this month in the British Medical Journal (BMJ), details the cost effectiveness of implementing strategies to reduce population sodium—like the “voluntary” sodium reductions for food manufacturers the Food and Drug Administration proposed last year. While presented as “proof,” this study is little more than an exercise in fantasy.
The researchers assume a linear, dose-response relationship between dietary sodium and blood pressure—meaning that for every increase in X mg of sodium there’s a corresponding X increase in blood pressure. They also assume that for every increase in blood pressure, there’s a corresponding increase in deaths. Lastly, they assume programs that nudge people to reduce their sodium will work. Thus, if all these assumptions are correct, the cost of implementing such programs balances out with the health benefits. The problem is, their assumptions aren’t supported by the research.
First, it requires little scientific background to realize that any trend between sodium and health cannot be linear. Humans require dietary sodium in order to live, so there is a low level at which health does not improve, but becomes worse. In fact, researchers have pointed to this sub-optimal level of sodium intake as a possible reason for why several large population studies have found that groups with extremely low sodium intake are more likely to die (they also found higher risk of mortality at the extreme upper end).
Furthermore, the research the BMJ study’s authors relied upon likely had skewed results because of the types of people on which they were based. As noted in our study and elsewhere, not everyone responds the same way to increases and decreases in dietary sodium. As Niels Graudal (a Camp 2 researcher) pointed out in commentary on the BMJ article, randomized control trials—the gold-standard of biomedical research—“have documented that there is no effect of blood pressure reduction on health outcomes in normotensives individuals.”
Salt’s role in hypertension and other aspects of human health is far from settled. That does not mean that for some people sodium reduction won’t help, but it does indicate that neither population-wide recommendations nor “soft regulation” of sodium are warranted by the existing evidence.
For the past four decades, health agencies have been pushing us to consume less sodium, even as Americans—and the rest of the world—have continued to consume roughly the same amount of sodium. This is despite the fact that processed foods have become saltier and we eat more processed foods as a culture. That said, the prevalence of hypertension has increased over the last two decades. These facts should prompt researchers to ask why this is the case, and to investigate other possible causes and solutions to hypertension.
Unfortunately, it seems no amount of evidence will stop those who cling to the old dogma. As researcher Sandro Galea put it: “We pay quite a bit of attention to financial bias in our work … 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.”
But don’t take my word for it. If CEI’s study proves anything, it’s that health decisions are intensely personal, that no solution works best for everyone, and that individuals must decide and test for themselves what health advice is most likely to benefit them.