Salt (or sodium—used interchangeably at the forum) is essential for all life, Germino pointed out. It’s a major determinant of blood volume and has other crucial roles in the body. “Salt’s retention mechanisms were very invaluable to our evolution,” he said.
Necessary, but in what quantity? Turns out, humans need only about 200 milligrams of salt daily to maintain normal body function. High levels of salt have been linked to elevated blood pressure, which contributes to development of heart disease. What should be our daily intake and is there enough evidence to change public health policy?
Dr. Lawrence Appel (l) of Johns Hopkins University and Dr. Michael Alderman of Albert Einstein College of Medicine share opposing views on the topic of salt consumption.
Photos: Bill Branson
The American Heart Association (AHA) first recommended lowering daily sodium intake to no more than a level teaspoon—about 3,000 milligrams—in 1986. By 2005, U.S. Dietary Guidelines for Americans set the general population maximum at 2,300 mg. High-risk populations—African Americans, people with hypertension, older age groups—should limit consumption to 1,500 mg. In 2011, AHA recommended 1,500 mg for everyone.
On average, Americans consume about 3,400 mg every day. That hasn’t changed significantly despite recommendations. So, salt intake remains high, but is it making us sick?
Avoiding the salt shaker won’t really help us eat less. Manufacturers add the vast majority, roughly 77 percent, of sodium we consume to food we buy. We tack on about 5 percent as we’re cooking and another 6 percent using the shaker at the table. About 12 percent of our salt intake is inherently in foods.
“Some of the worst culprits are bread and cereal products,” said Dr. Lawrence Appel of Johns Hopkins University, one of two presenters at the forum. “Pizza is particularly bad, at about 800 milligrams per slice.”
In addition to Appel, STEP invited an opposing presenter and two panelists for the discussion.
If salt is the villain in this affair of the heart, then Appel is the tough-love relationship coach reminding us of sodium’s well-documented misdeeds.
Numerous studies have shown that excess salt leads to hypertension, a major risk factor for heart disease, he said. Cut down on sodium, cut down on heart problems, Appel contended.
“If you reduce the sodium intake in the general population by 400 milligrams,” he said, “then it would be estimated that 20,000 heart attacks would be prevented,” according to one research model.
“Elevated blood pressure has been identified as the leading cause of preventable deaths, even greater than tobacco use,” Appel continued.
By 2030, projected costs related to hypertension and its consequences will be close to $400 billion, he said, noting that more than 100 trials support his position. “Estimated benefits of sodium reduction are substantial and warrant major public health efforts to reduce its intake,” he concluded.
Not so fast, said Dr. Michael Alderman of Albert Einstein College of Medicine. He agrees there are harmful levels of salt consumption—below 2 grams and above 5 grams of sodium per day. He said research shows “safe salt intake is between 2.5 and 5 grams a day—exactly what Americans and most of the world consumes.” Give salt the benefit of the doubt until we know more, definitively, about its effects—both positive and negative, he suggested.
“It’s an eminently reasonable hypothesis that reducing sodium intake—or lowering weight, or increasing exercise or a variety of techniques that we could apply to the whole population—would be a wise addition to our efforts to prevent cardiovascular events,” Alderman said.
But, studies haven’t yet looked at the whole picture, he said. “Skeptics—and I count myself as one—say blood pressure only reflects one of many physiological aspects,” he explained, “and the health effect of lowering sodium intake will be the result of all physiological effects.”
He said some of the same studies that show sodium increasing blood pressure also show other possibly significant health effects—decreased insulin sensitivity and increased sympathetic nerve activity, for example. No single physiological effect predicts morbidity and mortality, he contended. “No single effect can forecast health outcomes.”
In addition, there could also be unintended consequences to further reducing intake levels, Alderman said. “Physicians, public health practitioners and people in general need to know the effect of altering sodium intake on health—which will be the sum total of all the physiological effects we know and perhaps others we do not know.” Why not examine these other effects before making recommendations?
On the panel to address questions following the presentations are (from l) Appel, Clinical Center nutrition researcher Dr. Amber Courville, NHLBI dietitian Kathryn McMurry and Alderman.
Citing the 1980 low-fat diet recommendation that was widely issued and then rescinded 20 years later after further study, Alderman said we need more comprehensive research before lowering the salt-intake threshold.
Also, Alderman noted, there is no evidence that consuming less than 2 grams of sodium provides a health benefit and there are 5 observational studies that show harm—increased mortality and morbidity.
“Three solid, randomized trials show increased morbidity and mortality when 1.8 [grams] are consumed compared to 2.8 grams, hence solid evidence of harm and none of benefit,” he said. Those studies also showed that intakes above 5 to 6 grams cause harm.
“In fact,” Alderman emphasized, “the sodium story is just like most other essential nutrients—too much and too little are not good, but there is a broad range in the middle where health is not affected. Thus, like most essential nutrients, the relation of sodium intake to health is a ‘J’-shaped curve. Just like vitamin D, too little—less than 2 grams—can cause harm, and too much—above 5 grams—can also cause harm.
“Any recommendation to reduce salt below 2.5 grams should be preceded by randomized clinical trials, by some evidence that it would be both safe and beneficial,” he concluded.
Following presentation of both sides of the debate, panelists NHLBI dietitian Kathryn McMurry and Clinical Center nutrition researcher Dr. Amber Courville joined Appel and Alderman to address questions and comments from the audience.
The discussion ranged from changes in salt intake over the last 30 years, to the practicality of getting Americans to reduce their sodium consumption, to appropriate salt-retention levels for athletes to past efforts by food manufacturers to offer low-salt alternatives.
HHS’ers can view the full discussion online at http://videocast.nih.gov/launch.asp?17719.