Some Grains of Truth about Salt, Scientific Evidence, and Public Policy

September 16, 2013

Is salt bad for your health? Should everyone cut back? Does it pose a risk only for people with high blood pressure? Should policymakers regulate the amount of salt in our food?  Do we have the evidence we need to support such actions? Will we ever have it?

Debate has raged over these questions since the late 1960s. In a new review of half a century of studies, recommendations, meta-analyses, federal policies, and reports in the popular press, Mailman School professors Ronald Bayer, PhD, and Sandro Galea, MD, DrPH, along with sociomedical sciences doctoral student and journalist David Johns serve up a provocative new analysis of the case, such as it is, for reducing dietary salt. They also raise fresh and urgent questions about how to formulate policy when scientific evidence is ambiguous and contested.

The article was published in the December 2012 issue of Health Affairs. See abstract.

Some key moments in the salt debate:

  • Concerns were first raised over the level of salt in baby food. In 1970, a National Academy of Sciences committee found insufficient evidence of risk but nonetheless recommended no more than .25 percent added salt in baby food.
  • In 1977, the Senate’s Select Committee on Nutrition and Human Needs issued a report with the nation’s first salt goal: 3 grams per day (average consumption was 3–4 times that amount.) It was immediately controversial.
  • In the 1980s, several major studies, including the Framingham study, the Scottish Health Heart Study, and the vast, multinational Intersalt study failed to find a meaningful link between sodium intake and health outcomes.
  • In the late ‘80s and ‘90s, several meta-analyses found a minimal link: a large reduction in salt might cut blood pressure slightly in the general population.
  • In the 2000s, two large studies found evidence that cutting salt offered benefits in lowering blood pressure and reducing cardiovascular risk. But two 2011 Cochraine reviews—seen by many as the gold standard for literature reviews—raised doubts about overall health benefits.

“What’s striking about the salt debate,” write the authors, “is that the combatants cannot be neatly divided between the respected advocates of a mainstream position and a band of marginal dissidents. Respected scientists can be found on both sides of the divide.”

The salt saga raises key issues about how to formulate “evidence-based” policy, says Dr. Bayer, an ethicist and professor of sociomedical sciences who co-directs the school’s Center on the History and Ethics of Public Health.  “We concluded that it is a mistake for policymakers to pretend that the evidence is clearer than it truly is. Concealing scientific uncertainty does not serve science or the public.”

"We were interested in exploring the gap between the certitude of our public health action and the confidence of the science.  Understanding the reasons for the difference between the two may help guide us to more informed evidence-based practice," says Dr. Galea, Gelman Professor and chair of the school’s Department of Epidemiology.

In fact, the authors believe that the commonplace view that research evidence can be smoothly translated into action is overly simplistic. They call instead for a more nuanced and transparent weighing of evidence, costs, likely benefits, and possible unintended consequences.

This article originally appeared on the Mailman School of Public Health website.