IOM challenges traditional advice on low-sodium diet

Health experts are encouraging physicians to remain focused on reducing sodium in their patients’ diets amid controversy about appropriate levels sparked by an Institute of Medicine report.

The May 14 report said that although lowering consumption of sodium benefits health, there is no evidence that intake below 2,300 mg/day increases or decreases the risk of cardiovascular disease, stroke or all-cause mortality.

Levels below 2,300 mg/day might actually elevate risk of adverse health outcomes among people with cardiovascular disease, chronic kidney disease and diabetes, the 12-person IOM committee said. The committee included experts in endocrinology, epidemiology, internal medicine, nutrition and public health.

“Looking at sodium’s effects on blood pressure is not enough to determine dietary sodium’s ultimate impact on health,” said committee Chair Brian L. Strom, MD, MPH, a professor of public health at the University of Pennsylvania School of Medicine. “Changes in diet are more complex than simply changing a single mineral. More research is needed to understand these pathways.”

The findings ignited an uproar among some in the health community because they conflict with federal dietary guidelines and those issued by leading medical organizations, including the American Heart Assn.

The federal 2010 Dietary Guidelines for Americans advise the following Americans to consume no more than 1,500 mg/day of sodium: adults 51 and older; blacks; and people with chronic kidney disease, diabetes or hypertension. All other individuals age 2 and older should consume less than 2,300 mg/day of sodium.

The heart association goes further, recommending that everyone age 2 and older take in no more than 1,500 mg/day of sodium.

“While the American Heart Assn. commends the IOM for taking on the challenging topic of sodium consumption, we disagree with key conclusions,” said Nancy A. Brown, the organization’s CEO.

Elliott Antman, MD, a spokesman for the association, encouraged doctors not to be distracted by discussions about possible harm in low-sodium diets that are based on what he considers “flawed data.”

“There’s no disagreement about the most important public health message, which is that we need to urge patients to take in lower amounts of salt in their diet,” said Dr. Antman, a cardiologist at Brigham and Women’s Hospital in Boston.

Physicians should continue suggesting that patients read nutrition labels on items they buy and select products that are low in sodium, said Stephen Havas, MD, MPH, a professor of preventive medicine at Northwestern University Feinberg School of Medicine in Chicago. Doctors also should tell patients that when eating at a restaurant, they can ask for their food to be prepared without added salt, he said.

Considering that 77% of the sodium Americans consume each day comes from processed and restaurant foods, “the only way for most people to meet the current sodium recommendation is to cook from scratch and not use salt,” he said. “That’s not realistic for most people.”

Dr. Havas encourages physicians to advocate for the Food and Drug Administration to set limits on the amount of sodium that can be put in processed and restaurant foods. Such advocacy could include writing letters to legislators or President Obama, he said.

The American Medical Association has policy that calls for a stepwise, minimum 50% reduction in sodium in processed foods, fast-food products and restaurant meals during the next decade. The AMA urges the FDA to develop regulatory measures to limit sodium in processed and restaurant foods.

“We need to make it easy for the American public” to reduce sodium in their diets, Dr. Havas said. “Right now, it’s extremely hard.”

The risks of low levels

The average American consumes about 3,400 mg of sodium every day, which is equivalent to 1.5 teaspoons of salt, the IOM said. Data show that consuming excessive sodium is a risk factor for hypertension, which in turn increases the likelihood of cardiovascular disease, stroke and even death.

There are concerns, however, that a low-sodium diet could adversely affect certain risk factors, including blood lipids and insulin resistance, and thus potentially increase risk of cardiovascular disease and stroke, the IOM said.

The Centers for Disease Control and Prevention commissioned the IOM expert committee to assess the benefits and adverse outcomes, if any, of reducing the population’s sodium intake. The committee also identified data and methods gaps in studies and suggested ways to address them.

Committee members examined reports on sodium and direct health outcomes published between 2003 and 2012 and held a public workshop during which outside experts could discuss the issue. The direct outcomes assessed include cardiovascular disease and death.

They found studies on health outcomes are inconsistent in quality and insufficient in quantity to recommend lowering sodium intake levels below 2,300 mg/day. Study limitations include over- or under-reporting intake levels and incomplete collection of urine samples. Urine samples are used to determine sodium consumption based on an individual’s secretion. Low sodium intake (such as 1,840 mg/day) might increase the risk of adverse events among patients who have chronic heart failure with reduced ejection fraction and are receiving aggressive therapeutic regimens, the IOM said.

Those data, however, are based on studies conducted in another country where therapeutic regimens for CHF are different from those in the U.S., the report said. The committee called for similar studies to be conducted using regimens more closely resembling those in standard U.S. clinical practice.

With the exception of people with CHF, there’s no evidence of benefit in reducing sodium intake between 1,500 mg/day and 2,300 mg/day for populations often considered at risk, including those with diabetes and chronic kidney disease, the IOM said.

More randomized clinical trials are needed to better understand the impact of a low-sodium diet, committee members said. They recommend that future studies use a standard approach to measure sodium consumption and focus on levels between 1,500 mg/day and 2,300 mg/day.

The report doesn’t establish a healthy intake range because the committee was not asked to do so.

Salt in processed foods

A separate study shows sodium levels in processed food and fast-food items remain essentially unchanged since 2005, despite numerous calls from the public health community for the food industry voluntarily to reduce salt levels in their products. The findings were published online May 13 in JAMA Internal Medicine, formerly Archives of Internal Medicine. The study was conducted with the Center for Science in the Public Interest, a consumer advocacy group focusing on nutritional education.

Researchers examined the sodium content on the nutrition labels of commonly eaten processed foods and fast-food restaurant items in 2005, 2008 and 2011. Only foods that were marketed in all three years were included in the study.

They found that between 2005 and 2011, the sodium content in 402 processed foods declined by 3.5%, while levels in 78 fast-food restaurant products increased by 2.6%. Neither of the findings was statistically significant, said Dr. Havas, the study’s corresponding author.

The National Restaurant Assn. said the findings don’t indicate recent progress made by the food service industry in developing lower-sodium items for consumers.

“Only a small number of products were sampled from a limited number of brands, versus the thousands of menu items available to consumers,” said Joy Dubost, PhD, RD, director of nutrition and healthy living at the restaurant association.

Despite the relatively small sample size, Dr. Havas said the findings show that the voluntary approach to reducing sodium has failed.

“This issue will not go away unless the government steps in to protect the public,” he said. “The amount of sodium in our food supply needs to be regulated.”