November 2014 Issue

Spotlight on Sodium: How Much Is Too Much, and How Little Is Too Little?
By Judith C. Thalheimer, RD, LDN
Today's Dietitian
Vol. 16 No. 11 P. 26

It's a fact: People who consume high levels of sodium tend to have higher blood pressure and increased risk of cardiovascular disease.1,2 But how much is too much? And how little is too little? The 2010 Dietary Guidelines for Americans recommend the general population limit daily sodium intake to less than 2,300 mg, with high risk groups striving for no more than 1,500 mg.1 The American Heart Association (AHA) supports a 1,500 mg target for everyone.3 But a 2013 Institute of Medicine (IOM) report seemed to question parts of those recommendations, and data from new, high-powered studies published in the New England Journal of Medicine are feeding the controversy. Why is there so much confusion surrounding sodium recommendations? And what should dietitians and other health professionals be advising their clients and patients to do?

Americans and Salt
The average American consumes more than 3,400 mg of sodium per day.1 That's equivalent to 11/2 teaspoons of salt, more than twice the recommended 1,500 mg recommended by the AHA.2,4 People aged 51 and older and those of any age who are black or have hypertension, diabetes, or chronic kidney disease are even more responsive to the blood pressure–raising effects of sodium, so the official recommendation is set even lower, at 1,500 mg per day.1 About one-half of the US population falls into this lower category.1 The AHA recommends that everyone aim for this lower goal as a preventive measure. "As people age, their blood pressure rises," explains Lawrence Appel, MD, MPH, a professor of medicine at Johns Hopkins University and a spokesperson for the AHA. "Ninety percent of us will become hypertensive. To have a preventive rather than a reactive approach, we need to consider everyone high risk." A recent survey suggests that people aren't even aware of how much sodium is in their diets. Nearly 97% of the 1,000 people surveyed either couldn't estimate how much sodium they eat daily or underestimated their intake, often by as much as 1,000 mg.5

The science is unequivocal that all this excess sodium has serious health implications. Consuming too much sodium is associated with stroke, heart failure, osteoporosis, stomach cancer, and kidney disease.3 Sodium holds excess fluid in the body, increasing blood pressure.3 Hypertension is one of the biggest risk factors for cardiovascular disease and death, but it's modifiable.6 Reducing dietary sodium intake and increasing dietary potassium are the most common strategies for addressing hypertension.6

Conflicting Evidence
Few would dispute that the average American's sodium intake is too high. "The vast majority are consuming excess sodium and can benefit by lowering sodium intake to reduce blood pressure and cardiovascular risk," Appel says. There's some controversy, however, on how low to go. "Too much sodium is bad for you," says Brian L. Strom, MD, MPH, chancellor for Biomedical and Health Sciences at Rutgers University, "but too little sodium might be bad for you as well." In 2013, the Centers for Disease Control and Prevention (CDC) asked the IOM to review emerging research indicating that low sodium intake may increase health risks. Strom, who led the resulting IOM Committee on the Consequences of Sodium Reduction in Populations, explains that the committee looked at all health outcomes, not just blood pressure. "Lowering sodium intake does decrease blood pressure, but when you go from a high-sodium diet to a moderate intake, heart outcomes are better, even when the effect of sodium on blood pressure is removed. Then, when you go from moderate sodium intake to low, blood pressure continues to drop, but the benefit on real clinical outcomes does not. In fact, the rate of heart attacks and other adverse clinical outcomes in people on very low sodium diets appears to increase."

The IOM report concluded that, while high levels of sodium intake definitely are related to risk of cardiovascular disease, there aren't enough good data on health outcomes to determine what impact sodium intake below 2,300 mg per day has on the risk of heart disease, stroke, or other causes of death in the general US population.2 In particular, the report found there are no data indicating benefit from dietary sodium levels that low, with some data suggesting possible harm. When they looked at studies on direct health outcomes for high-risk groups, the committee concluded that "there is no evidence that the subgroups should be treated any differently than the rest of the general population," Strom says. "Thus," he concludes, "overall, the evidence does not support recommendations to lower sodium intake to or below 1,500 mg a day."

The AHA, however, stands by its recommendation that all Americans should strive for the sodium intake of 1,500 mg or less per day. "The IOM report was not a comprehensive review of evidence," Appel says. "It focused on a certain type of research, namely observational epidemiologic studies. The committee acknowledged the limitations of these studies. Interestingly, it did not review evidence on the link between excess sodium intake and higher blood pressure. You cannot make a decision on the health effects of sodium without taking into account the blood pressure–lowering effects of decreasing sodium intake." In the Dietary Approaches to Stop Hypertension (DASH) trial, people who lowered their sodium intake from 2,500 mg to 1,500 mg reduced their blood pressure more than those who went from 3,300 mg to 2,500 mg.7

In August 2014, two studies in the New England Journal of Medicine raised more questions about the value of very low sodium intake. The Prospective Urban Rural Epidemiology (PURE) study used the level of sodium and potassium in urine samples to estimate intake in more than 100,000 people in 17 countries.6 In one analysis, the researchers compared excretion levels with risk of death and cardiovascular events. An estimated sodium intake between 3,000 mg and 6,000 mg per day was associated with a lower risk of death and cardiovascular events than either a higher or lower estimated level of sodium intake.8 Another analysis looked at sodium excretion and blood pressure. Only 4% of participants had estimated sodium intake in line with US guidelines, but sodium intake wasn't related to blood pressure in these people.6,7 According to an analysis of these studies, the results call into question the usefulness of reducing dietary sodium as a population-based strategy for reducing blood pressure.6 The authors acknowledge there are limitations to their studies.7,8 Appel is emphatic that observational epidemiologic studies such as these are misleading. "The large sample size of these studies gives the impression of high quality, but they have major methodological problems. It is very difficult to estimate sodium intake. You have to take multiple urine samples over 24 hours, not just do spot testing as was done in these new studies. There is a high risk of reaching a false conclusion with this kind of study."

There are other concerns with recommending very low sodium intake. "In this case, I'm afraid the perfect is the enemy of the good," Strom says. "It's extremely difficult to consume only 1,500 mg of sodium a day. If people try to get their sodium intake down to 1,500 and fail, they may give up." Appel says it can be discouraging dealing with today's food environment. Seventy-five percent of people's daily sodium comes from processed or restaurant food, and the average restaurant sandwich has 1,000 mg of sodium or more.3,4 It can be hard to consume only 1,500 mg without cooking all meals from scratch.4 There's also the matter of overall nutrition. When the IOM created the original Dietary Reference Intakes for sodium in 2004, 1,500 mg was set as the Adequate Intake.9 "We know the human body needs only 500 mg of sodium a day to survive, but at that level it would be impossible to get enough of the other nutrients we need in our diets; 1,500 mg was felt to be a minimum needed to ensure proper nutrition," Strom says. So will encouraging people to aim for 1,500 mg or lower compromise their overall nutritional health? Appel says no. "At 1,500 it's not difficult to get other nutrients, especially if people avoid processed food. The DASH Sodium clinical trial was able to provide a healthful balanced diet that was also low in sodium."

The Larger Issue
According to Marisa Moore, MBA, RDN, LD, a spokesperson for the Academy of Nutrition and Dietetics, the debate over sodium recommendations is "complicated, and it's been going on for decades. It seems as if there's no solid answer. The problem is that the research for a generalized recommendation just isn't there." Appel agrees. "Part of the problem is that it takes a lot of effort and resources to do quality sodium research," he says.

Meanwhile, perhaps the debate over numbers is obscuring the larger issue. "When considered collectively, the evidence does link increased sodium intake with an increased risk of cardiovascular disease," says Jessica Lee Levings, MS, RD, LD, a policy analyst/federal contractor for the CDC. "Given current levels of sodium consumption, reducing intake would improve public health."

"In the case of sodium, part of the problem is we're focusing on numbers," Appel says. "To some extent the numbers become a diversion from the goal. It's the process that's important. Any change is good change." Strom agrees that the message goes beyond the numbers. "From a population point of view, the message is to not eat too much or too little sodium," Strom says. "If you currently eat excessive amounts of sodium, try to eat less."

Where Most Sodium Comes From
To reduce sodium consumption, the 2010 Dietary Guidelines for Americans recommend using Nutrition Facts labels to choose foods low in sodium, eating more fresh whole foods and fewer processed foods, cooking at home, and asking for lower-sodium options in restaurants.1 Most sodium in the American diet doesn't come from the salt shaker.3 "It's important to remember that the majority of sodium we're consuming is already in the ingredients we buy at the grocery store and bring home to cook," Levings says. "To reduce sodium intake, people must read labels and choose lower-sodium options."

Those labels contain some information that might be surprising to many, Moore says. "A serving of potato chips generally has less sodium than two tablespoons of salad dressing. And it's not just packaged foods that you have to watch out for," she says. "Deli meats are really high, and some foods, like cheeses and other dairy products, are naturally high in sodium. I recommend Swiss cheese as a lower-sodium choice." Sometimes it isn't the amount of sodium in a food that's the problem, but the amount of that food that's consumed. "The No. 1 source of sodium in the American diet is breads and rolls," Levings says. "They aren't necessarily high-sodium foods, but we eat so much that the sodium really adds up."

Alternatives That Boost Flavor
The American palate is so accustomed to the taste of salt that people may not perceive it in their foods. To change the palate, Moore teaches clients that there are many different ways to achieve flavor besides using salt. "I like to cook, and I think salt is important to bring out flavors. Getting clients to increase vegetable intake is important, and a sprinkle of salt can help make veggies palatable," Moore says. She recommends using salt as a finisher, adding it at the end of cooking. Instead of marinating foods in sodium-laden salad dressings or commercially prepared marinades, Moore recommends citrus juices. "Flavored vinegars are a great option as well," she says. "There are a lot of options out there now. For an Asian flair, try marinating in sesame oil with rice vinegar. Don't be afraid to experiment in the kitchen." Hot peppers add a kick without salt, and herbs and spices are a great way to enhance the flavor of foods, but Moore cautions that cutting out all salt in favor of herbs and spices may not go over well right away. "I recommend cutting salt by 50% or even 25% at first to start getting used to new flavors and actually appreciating the underlying flavor of the food."

Individualized Recommendations
While gradual salt reduction is wise, recommendations and advice should be tailored to the individual. "Ideal sodium levels differ from population to population and even among disease states," Moore says. "I encourage RDNs to deliver customized nutrition solutions." Even in a healthy population, needs will vary.

"[Olympic gold medalist] Michael Phelps eats over 10,000 calories a day. There's no way he could ever limit his sodium intake to 1,500 mg," Appel says. "There's science, and then there are practical considerations." Setting reasonable goals is practical as is meeting clients where they are and aiming for incremental change. The high-sodium content in processed and restaurant food can make changing a challenge.

Appel points out that some interventions don't require so much individual change. Reduction in trans fat intake was achieved by changing processed foods, not habits. "Given the food supply, American's high-sodium intake levels are not surprising," he says. "It would make a big difference if we could inch the food industry toward lower-sodium content." Some companies are heeding the call. Lower-sodium versions of spaghetti sauce, for example, already are available in stores.

Diet Quality Is the Goal
However, helping clients reduce sodium intake alone isn't the whole answer. Focusing on eating higher quality, nutrient-dense foods should be the focus. "Sodium intake can say a lot about overall diet quality," Moore says. "If someone is eating a lot of high-sodium foods, it's often a sign that their overall diet isn't as nutritionally balanced as it should be." Improving overall diet can be the most essential recommendation. The PURE study looked at potassium as well as sodium.

Based on their results, the authors propose that reducing sodium intake while eating a high-quality diet rich in potassium might achieve greater health benefits than reducing sodium alone.6 Their findings suggest that the effect of sodium on blood pressure may be dependent on the background diet.7 Likewise, the DASH studies demonstrated that the total eating pattern affects blood pressure.1 Encouraging clients to increase intake of fruits and vegetables can be helpful in lowering their cardiovascular risk. Both are naturally low in sodium and high in potassium and have numerous other recognized heart-healthy properties.

Overall, a consensus on sodium recommendations is less important than the general goal of improving diet quality and decreasing excessive sodium intake. Working with clients to develop individualized plans for a healthful diet that will lower sodium intake can have a major impact on their blood pressure and overall risk of long-term health consequences such as hypertension. Regardless of the current state of the research and any questions regarding recommendations, "there is no question that decreasing excessive sodium intake is good for your health," Strom says. "People should read labels, avoid the highest sodium foods, and remember that, as in many things, moderation is the key."

— Judith C. Thalheimer, RD, LDN, is a freelance nutrition writer, a community educator, and the principle of JTRD Nutrition Education Services.

 

References
1. US Department of Agriculture, US Department of Health and Human Services. Dietary Guidelines for Americans, 2010. 7th ed. Washington, D.C.: US Government Printing Office; 2010.

2. Institute of Medicine. Sodium Intake in Populations: Assessment of Evidence. http://www.iom.edu/~/media/Files/Report%20Files/2013/Sodium-Intake-Populations/SodiumIntakeinPopulations_RB.pdf. Updated May 2013.

3. About Sodium (Salt). American Heart Association website. http://www.heart.org/HEARTORG/GettingHealthy/NutritionCenter/HealthyEating/About-Sodium-Salt_UCM_463416_Article.jsp. Updated June 23, 2014. Accessed September 1, 2014.

4. Study questions how sharply US should cut the salt. AP website. http://bigstory.ap.org/article/study-questions-how-sharply-us-should-cut-salt. Updated May 14, 2013. Accessed September 1, 2014.

5. Salt E-Update. New AHA Consumer Sodium Reduction Campaign. Center for Disease Control and Prevention. July 24, 2014.

6. Oparil S. Low sodium intake — cardiovascular health benefit or risk? N Engl J Med. 2014;371(7):677-679.

7. Mente A, O'Donnell MJ, Rangarajan S, et al. Association of urinary sodium and potassium excretion with blood pressure. N Engl J Med. 2014;371(7):601-611.

8. O'Donnell M, Mente A, Rangarajan S, et al. Urinary sodium and potassium excretion, mortality, and cardiovascular events. N Engl J Med. 2014;371(4):612-623.

9. Institute of Medicine. Dietary Reference Intakes: Water Potassium, Sodium, Chloride, and Sulfate Report at a Glance. http://www.iom.edu/Reports/2004/Dietary-Reference-Intakes-Water-Potassium-Sodium-Chloride-and-Sulfate.aspx. Updated September 4, 2013. Accessed September 9, 2014.