U.S. public health guidelines have pushed for lower sodium consumption for more than 30 years. Since 2003, healthy adults have been told to limit sodium intake to 2,300 milligrams per day, while those at risk for hypertension were told to limit it to 1,500 mg per day. The 2010 Dietary Recommendations for Americans may recommend even lower levels, while setting in motion policies to limit salt in processed foods.

But what if we eat so much salt not because we just like the taste or can't avoid it, but because we need to for our bodies to function normally? What if our brains are controlling our appetite for salt?

David A. McCarron, Alexandra G. Kazaks and Judith S. Stern of the Department of Nutrition at the University of California at Davis, along with Joel C. Geerling, then at the Department of Anatomy and Neurobiology at Washington University, have discovered new evidence that suggests normal sodium levels are substantially higher than the level recommended by government guidelines.

Although first set to address the health risks of hypertension, the guidelines have expanded to include healthy people. This study is concerned with the advice that people not at risk for hypertension lower salt intake.

It examined neuroscience research on sodium appetite as well as data from sodium intake studies worldwide. The analysis, "Can Dietary Sodium Intake Be Modified by Public Policy?" was posted online this morning in the Clinical Journal of the American Society of Nephrology. It concludes that the data suggest physiological controls maintain sodium levels within a narrow range, so public policy intervention is unlikely to have an effect on human salt consumption.

Neurological research has demonstrated that animals in the laboratory "expressed an ingestive behavior designed to assure survival when threatened by sodium depletion." In other words, when salt levels fell dangerously low in animals, they sought out foods that were higher in salt until they re-established normal levels. Dr. McCarron and his colleagues posit that human beings engage in similar behaviors in order to maintain a normal sodium level.

In order to determine what that level might be, they evaluated 24-hour urinary sodium excretion from 19,151 individuals collected in 62 previously published surveys from 33 countries. They determined that adult human sodium intake ranges between 2,700 and 4,900 mg per day and concluded that "the likelihood that these diverse sources of data ... have defined the same range of sodium intake in adult humans purely by chance is exceedingly small."

They believe this data contradicts the idea that salt consumption has drastically increased in Western societies, since the range was the same across diverse cultures.

"We've been wired in our brains to consume salt within a very narrow range, to maintain our bodies' functions," said Dr. McCarron. "That range, at its very lowest limit, is 20 percent higher than what the government is telling us is the upper limit for the normal population. The average around the world ... is over 60 percent higher than what the government is telling us that we should consume."

Ed Stricker, a professor of neurology at the University of Pittsburgh and an expert in salt appetite, raises objections to the way Dr. McCarron and his colleagues analyzed data, but he ultimately supports their conclusions.

Dr. Stricker pointed out that while some animals will seek out salty food to replenish low sodium levels, there is no evidence that human beings have evolved similar behaviors. Instead, he thinks that Dr. McCarron and his colleagues should have paid more attention to the physiological mechanisms that conserve sodium when sodium levels are too low. What Dr. McCarron attributed to human behavior (seeking out food with more salt), Dr. Stricker attributes to physiological conservation of salt.

Dr. Stricker also said some people do follow the low-salt diet recommendations; consequently, he expresses concern that low sodium intake could be just as dangerous as too high an intake. "Your blood pressure is going to be too low, your kidney function isn't going to be what it should be, there are a host of secondary problems," he said.

Looking for more from the Post-Gazette? Join PG+, our members-only web site. You'll get exclusive sports content, opinion, financial information, discounts from retailers and restaurants, and more. Our introduction to PG+ gives you all the details.