Don’t worry about sodium . . . Cut back on sodium . . . Consume a lot less sodium . . . Don’t go too low in sodium. Over the past few decades, Americans have been subjected to shifting messages about sodium (a main component of salt) and were undoubtedly baffled even more by a recent report from the Institute of Medicine (IOM), which suggested that a very low sodium intake could be bad for some people. Confused? We don’t blame you.
A salty tale
For years health and nutrition experts emphasized reducing dietary fat and cholesterol and seemed to be less concerned about sodium. But as evidence mounted that excess sodium increased the risk of high blood pressure—a leading cause of heart attacks, strokes and kidney failure—sodium took a more central place in dietary advice, and health officials began advising lower limits for more people.
In 2005 the government’s Dietary Guidelines recommended no more than 2,300 milligrams of sodium a day (the amount in about a teaspoon of salt) and 1,500 milligrams for people at higher cardiovascular risk—everyone over 50, all African Americans and anyone with hypertension, diabetes or chronic kidney disease. (Previous guidelines had just said to choose and prepare foods with less salt and, before that, to keep sodium intake “moderate.”)
Because 70 percent of U.S. adults fall into the higher-risk category, other health experts, notably the American Heart Association (AHA), began advising a 1,500-milligram daily limit for everyone, regardless of age and health status.
Research has consistently shown that when people reduce sodium, blood pressure drops—especially in those who already have elevated blood pressure or are “salt sensitive” (that is, their blood pressure is more responsive to sodium intake). For example, studies on the DASH (Dietary Approaches to Stopping Hypertension) eating plan, which restricts sodium to either 2,300 or 1,500 milligrams a day, have found that the diet reduces blood pressure at both sodium levels, but more so at the lower limit. (Besides lowering sodium, DASH also emphasizes fruits and vegetables and low-fat and nonfat dairy foods, along with whole grains, fish, poultry and nuts.)
According to the World Health Organization, hypertension is a leading factor in worldwide deaths and can be prevented by reducing salt intake and making other lifestyle changes.
In addition, there are other reasons to lower your sodium intake. A high intake can make blood vessels less flexible, which may cause or worsen atherosclerosis, independent of sodium’s effect on blood pressure. Excess sodium may also impair kidney function in some people, and, by increasing calcium in urine, may increase the risk of kidney stones. There’s concern about bone loss, as well, since sodium increases calcium excretion in urine, which causes calcium to be leached from bone. Lastly, as the IOM reported, some evidence links higher sodium intake to increased risk of stomach cancer.
Reigniting the sodium debate
In May the IOM shook things up when it announced that, despite current sodium recommendations, very low levels are not necessarily better and may even be harmful. The IOM is an independent nonprofit organization that convenes expert committees to examine research and advises the government and the public about health issues. The Salt Institute and other food industry groups welcomed the news, arguing that there should not be population-wide recommendations for severe sodium reduction.
The IOM report analyzed close to 40 studies that looked at sodium’s effect on cardiovascular disease and death. One key finding was not surprising: The evidence confirmed that higher levels of sodium are associated with increased risk. But the other findings drew most of the media attention—that very low sodium intake could be risky for some people, particularly those with moderate to severe congestive heart failure who are undergoing aggressive (but not standard) treatment. Under certain circumstances (such as heart failure or excessive sweating), too little sodium may cause adverse events due to unpredictable changes in blood volume, which can result in inadequate blood flow to organs.
More startling, the report found no evidence of benefit—and some evidence “suggesting” adverse health outcomes—in people with diabetes, chronic kidney disease or heart disease who consumed less than 2,300 milligrams of sodium a day.
The IOM panel concluded that there is clearly enough evidence to support recommendations that people who consume excess sodium should lower their intake, but not enough for anyone to aim for less than 2,300 milligrams of sodium a day—including those at higher risk for cardiovascular disease.
Overheated headlines about salt
Many of the media reports that followed might have made you think you don’t have to worry about salt anymore—or perhaps even that you should consume more salt. One article declared that a “low salt intake may be unhealthy,” for instance, while another encouraged readers to “go ahead, order a side of fries.” Several blogs said that salt “isn’t so bad after all.”
But the IOM report really just said that there wasn’t enough evidence to come to any definite conclusions of either benefit or harm from severe sodium restriction (less than 1,500 milligrams a day), compared to 2,300 milligrams. This was largely due to the fact that the studies reviewed were limited in both quality and quantity and hard to compare because they varied so widely in design. In addition, most of the research was observational, so it doesn’t prove cause and effect. It’s possible, for instance, that when people are diagnosed with cardiovascular or other chronic disease, they start to consume less sodium, not the other way around. Moreover, the report could not say what an optimal sodium intake is and instead called for more clinical trials to help determine this.
Meanwhile, the AHA stands by its guidelines that everyone should consume no more than 1,500 milligrams of sodium a day, while the Academy of Nutrition and Dietetics continues to support the government’s Dietary Guidelines, which advise 1,500 milligrams for most people.
Putting it into perspective
The debate over whether to aim for 1,500 or 2,300 milligrams of sodium a day is irrelevant for most people. For one thing, Americans consume far more sodium than either of these limits—3,400 milligrams a day, on average. Getting down to just 2,300 milligrams would prevent tens of thousands of heart attacks and strokes a year, some experts have predicted. Second, it’s very hard to go as low as 1,500 milligrams, especially if you are an active or larger person who needs more calories (and thus consumes more sodium). The only way to do this is to cook from scratch using mostly unprocessed whole foods. In fact, just 5 percent of American adults reach the 2,300-milligram limit and less than 1 percent achieve the stricter limit, according to the Centers for Disease Control and Prevention (CDC). A 2012 paper published in the American Journal of Public Health called the 1,500-milligram limit “aspirational,” not necessarily achievable.
Most Americans are also not likely to ever meet the 1,500-milligram mark (and will continue to struggle to get down to even 2,300 milligrams) simply because our food supply is loaded with sodium. Despite appeals for the food industry to reduce sodium in processed and fast foods, a study in JAMA Internal Medicine in May reported that sodium levels did not significantly change between 2005 and 2011. Rather than leave it up to food companies to voluntarily lower sodium, the authors are calling on the government to regulate the amount of sodium allowed in processed food.
Bottom line: It will be interesting to see what the government decides to do with the IOM’s findings, since it is not obligated to use them when making its recommendations. We won’t know until the next version of the Dietary Guidelines comes out in 2015. But until then, as virtually all health experts—including the IOM panel—agree, it’s still prudent to cut down on sodium as much as possible. You can do this mainly by limiting highly processed foods (such as canned soups and frozen meals) and how much you eat out, since most restaurant fare is so salty. About 75 percent of the sodium in the U.S. diet comes from those sources, so always check the sodium content listed on food labels and, if available, on menus.
Keep in mind that reducing sodium is just one way to help maintain healthy blood pressure levels. Also essential is to eat a healthy diet that includes lots of potassium-rich foods (as advised by the DASH diet), be more active, lose weight if you’re overweight, keep alcohol intake moderate and not smoke. For many people, such measures are even more important than lowering sodium.