Most Dietary Sodium, by Far, Is in Food Prepared Outside the Home

Marcia Frellick

May 09, 2017

MINNEAPOLIS, MN — By far most of the sodium Americans ingest, nearly 71%, comes from foods prepared outside the home, new research indicates[1]. Sodium found naturally in foods consumed accounts for 14%, and salt added in the course of preparing food at home amounts to 5.6% of intake, it also found.

Only 4.9% of ingested sodium comes from salt shakers at the table at home, suggests the study, published in the May 9, 2017 issue of Circulation with lead author Dr Lisa J Harnack (University of Minnesota, Minneapolis).

The study's message for public health, Harnack told heartwire from Medscape: "Salting less at home is a good idea, but it won't get you there in terms of reaching sodium targets."

The findings are important for steering national efforts to bring sodium intake down, say Dr Lawrence J Appel and Kathryn Foti (Welch Center for Prevention, Epidemiology, and Clinical Research, Baltimore, MD) in an accompanying editorial[2].

They are also consistent with the 2010 Institute of Medicine recommendations targeting commercially processed foods in a gradual step-down process as the best way to reduce sodium nationwide and therefore reduce risk of hypertension, coronary heart disease, MI, and stroke, they write.

"This is an important observation that supports reducing the content of commercially processed and prepared foods as a broad effective strategy for reducing sodium intake in the United States."

Physicians, Consumers Can Help

Physicians and patients also should play a role, according to Appel and Foti. Patients can swap lower-sodium versions of favorite foods and take advantage of resources such as information on sodium from the American Heart Association. And some restaurants offer information on sodium levels or will reduce sodium levels in dishes upon request.

"Patients also have an escalating role in advocating for changes to the food supply," they write.

Physician advice to reduce sodium is known to help, but only about one-fourth of patients say their doctor has given them such advice, according to the editorialists. Given the findings of this study, physicians should stress product selection first and then encourage adding less salt at home, though the latter won't have much effect on its own, they note.

Data Gathered in Three Regions

The researchers gathered data between December 2013 and December 2014 from a convenience sample of 150 people in each of three geographic areas: Birmingham, AL; Palo Alto, CA; and Minneapolis–St Paul, MN. Participants, ages 18 to 74 years old, were chosen from each of four race/ethnic groups (blacks, Asians, Hispanics, and non-Hispanic whites) in equal numbers of men and women.

Notably, salt added to food outside the home still was the biggest contributor to total sodium intake in the Alabama cohort, but it had the highest percentage of salt added at the table, at 9.5%, compared with 3.4% in California and 2.3% in Minnesota.

That 75% of African Americans in the study were in the Birmingham cohort was a potential confounder in the analysis. It's hard to say whether some differences were a product of race or geography, the editorialists point out.

Another notable finding was that younger consumers had higher percentages of sodium from sources outside the home than older people (75% vs 67.4% to 70.5%, respectively), probably because they are eating out more and choosing more convenience foods, Harnack explained.

"That says something about the generation coming up," she said. "It's going to be more important in the future than today to lower the sodium in food products."

Information on sodium consumption was gathered in several ways, going beyond the standard diet-diary recall method. Participants were asked in telephone interviews to recall everything consumed in the past 24 hours, four times in 11 days.

When salt was added at home, participants were asked to shake the same amount of salt they used each time into a plastic bag. Those samples were mailed to the researchers.

"We had some of them do urine samples as well so we felt more confident about the self-report data, and we found good correspondence between the amount of sodium in the urine and the amount reported," Harnack said.

They used a dietary analysis software program called Nutrition Data System for Research to calculate sodium levels above what is naturally found in foods for foods prepared outside the home in restaurants or grocery stores.

Intake Consistently High

Other studies have shown that Americans consume sodium at levels well above the recommended level of 2300 mg a day. This study was no exception. It found an average of 3501 mg a day, more than 50% over the recommended amount.

As for the progress in lowering sodium levels, Harnack said, "A number of companies have pledged to lower the sodium content in their food products. With gradual reductions, your palate actually adjusts pretty soon."

The FDA has recommended that the food industry lower sodium levels, she notes, but has not mandated that.

In 36 countries, according to the report, there are voluntary sodium targets for certain foods.

"In the United Kingdom, this approach resulted in about a 15% (560-mg/day sodium, or 1.4-g/day salt) reduction in the average population sodium intake from 2003 to 2011 and was associated with significant decreases in blood pressure and cardiovascular disease deaths over the same time periods," the report says.

Funding for the study was provided through the Centers for Disease Control and Prevention. The findings and conclusions in this report do not necessarily represent the official position of the Centers for Disease Control and Prevention, the National Institutes of Health, or the US Department of Health and Human Services. The authors have no relevant financial relationships. Foti is supported by the National Heart, Lung, and Blood Institute, National Institutes of Health. Appel has no relevant financial relationships.

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