Sodium Intake Among Adults --- United States, 2005?2006

Excessive dietary sodium consumption increases blood pressure, which increases the risk for stroke, coronary heart disease, heart failure, and renal disease (1). Based on predictive modeling of the health benefits of reduced salt intake on blood pressure, a population-wide reduction in sodium of 1,200 mg/day would reduce the annual number of new cases of coronary heart disease by 60,000---120,000 cases and stroke by 32,000---66,000 cases (2). Dietary Guidelines for Americans 2005 recommends that specific groups, including persons with hypertension, all middle-aged and older adults, and all blacks should limit intake to 1,500 mg/day of sodium (3). These specific groups include nearly 70% of the U.S. adult population (4). For all other adults, the recommended limit is <2,300 mg/day of sodium. To estimate the proportion of adults whose sodium consumption was within recommended limits, CDC analyzed data from the National Health and Nutrition Examination Survey (NHANES) for 2005?2006, the most recent data available. Estimated average sodium intake and sources of sodium and calories by food category also were analyzed. This report summarizes the results of that analysis, which determined that only 5.5% of adults in the ≤1,500 mg/day group, and only 18.8% of all other adults consumed <2,300 mg/day. Overall, 9.6% of all adults met their applicable recommended limit. To help reduce sodium intake to below the recommended limits, food manufacturers and retailers can reduce sodium content in processed and restaurant foods, public health professionals and health-care providers can implement sodium reduction strategies and educate consumers about sodium, and consumers can modify their eating habits.

Data from the 2005?2006 NHANES,* a continuous survey of the health and nutritional status of the U.S. civilian, noninstitutionalized population, were used to estimate the daily sodium intake of adults aged ≥20 years. Approximately 71% of the adults (4,773 of 6,719) completed a physical examination component in NHANES mobile examination centers. Blood pressure measurements and one 24-hour dietary recall were obtained during examination. Another 24-hour dietary recall was obtained by telephone 3--10 days later. The final analytical sample consisted of 3,922 persons, after 253 participants were excluded because their record lacked a blood pressure measurement and 598 other participants were excluded because they had fewer than 2 days of dietary recall measurements. Mean blood pressure was calculated as an average of the available blood pressure measurements, with 95% of participants having two or three measurements. Participants were identified as hypertensive if they were on antihypertensive medication or if they had a mean systolic blood pressure of ≥140 mmHg or a mean diastolic blood pressure of ≥90 mmHg. The weighting of the 2-day dietary subsample took into account the complex multistage probability design, survey nonresponse, and poststratification in representing the U.S. civilian, noninstitutionalized population. Mean values for daily sodium and caloric intakes were calculated as averages of two dietary recalls. Daily sodium intake was calculated for two groups. The first group consisted of non-blacks aged 20--39 years, without hypertension, whose sodium consumption was recommended to be <2,300 mg/day. The second group consisted of all adults aged ≥20 years with hypertension, all adults aged ≥40 years without hypertension, and blacks aged 20--39 years without hypertension, whose sodium consumption was recommended to be ≤1,500 mg/day (Box).

To identify the major food sources of sodium, CDC categorized all foods reported as consumed by each participant into nine major groups, in accordance with the U.S. Department of Agriculture food coding scheme: 1) milk and milk products; 2) meat, poultry, fish, and mixtures; 3) eggs; 4) legumes, nuts, and seeds; 5) grain products (including foods in which grains are the primary ingredient, such as pizza); 6) fruits; 7) vegetables; 8) fats, oils, and salad dressings; and 9) sugars, sweets, and beverages.† Subgroups of the four food groups that contributed more than 5% of sodium intake (grains; meat, poultry, fish, and mixtures; vegetables; and milk and milk-based products) also were categorized. Sodium density, a measure that allows for comparison of sodium intake without confounding the related associations between total intakes of calories and sodium, was defined as milligrams of sodium per 1,000 kcal. Percentages and mean value estimates with standard errors were calculated using statistical software to account for the complex sampling design. Percentages of daily sodium intake for each food group were calculated by dividing the sodium intake in milligrams from each food group by the total sodium intake from all food consumed (in milligrams) and multiplying by 100. Percentages of daily energy intake were calculated using the same procedure. Differences in means were tested for statistical significance using the unpaired Student t test. Statistically significant differences in proportions were determined using the chi-square test. Results were considered statistically significant at p<0.05.

During 2005?2006, only 9.6% of all participants met the applicable 2005 recommended dietary limit for sodium (5.5% among the ≤1,500 mg/day group; 18.8% among the <2,300 mg/day group) (Table 1). U.S. adults consumed an average of 3,466 mg/day of sodium (Table 2). Most of the daily sodium consumed came from grains (1,288 mg; 36.9%) and meats, poultry, fish, and mixtures (994 mg; 27.9%), followed by vegetables (431 mg; 12.4%). Average daily sodium and calories consumed was 3,691 mg and 2,272 kcal for the <2,300 mg/day group and 3,366 mg and 2,068 kcal for the ≤1,500 mg/day group (Table 2). Although the ≤1,500 mg/day group consumed statistically significantly less sodium (p<0.001) and calories (p<0.001) than the <2,300 mg/day group, no difference was observed in overall sodium density or in eight of the nine main categories. Small but statistically significant differences in density were observed for two of the grain subcategories, one of the meats subcategories, and one of the vegetables subcategories. The ≤1,500 mg/day group consumed less sodium and calories from grains (1,205 mg versus 1,474 mg of sodium and 704 kcal versus 839 kcal) and sugars, sweets, and beverages (118 mg versus 138 mg of sodium and 286 kcal versus 361 kcal). However, that group consumed more sodium and calories from certain types of vegetables (109 mg versus 74 mg of sodium and 42 kcal versus 29 kcal).

Reported by

J Peralez Gunn, MPH, EV Kuklina, MD, PhD, NL Keenan, PhD, DR Labarthe, MD, PhD, Div for Heart Disease and Stroke Prevention, National Center for Chronic Disease Prevention and Health Promotion, CDC.

Editorial Note

Overall, 1 in 10 adults met their applicable recommendation for sodium intake during 2005--2006. The ≤1,500 mg/day group consumed more than double their recommended intake limit, and the <2,300 mg/day group exceeded their recommended intake limit by >1,300 mg. Previous reports on sodium intake in U.S. adult populations also reported high daily sodium intake (range: 2,933--4,178 mg) (1,5,6), and low proportions of persons whose intake was within limits <2,300 mg/day (range: 7.2%--24.4% among race/sex groups) (7). In contrast to Dietary Guidelines for Americans 2005, the American Heart Association recently encouraged all adults to eat <1,500 mg/day of sodium (8). If that guideline were applicable in 2005--2006, an even greater proportion of adults would be consuming more sodium than recommended.

In the United States, an estimated 77% of dietary sodium intake comes from processed and restaurant foods and approximately 10% comes from table salt and cooking (9). In this study, the majority of sodium came from the food categories from which the most calories were consumed, foods that might not taste salty. Grains contributed the largest amount of sodium and calories, followed by meats. Grains included foods that were highly processed and high in sodium (e.g., grain-based frozen meals and soups) and foods eaten frequently, such as breads. Intake of sodium from meats was higher than might be expected, likely because the category includes lunchmeats and sausages. In contrast, fresh fruits and vegetables inherently contain little sodium. However, vegetables were the third largest contributor, partly because the vegetable category contained vegetable-based soups and sauces, white potatoes (including potato chips, fries, and salads), and canned vegetables. An analysis of persons aged ≥2 years that used the same data set but a more detailed categorization found similar results: yeast breads, chicken and mixed chicken dinners, pizza, pasta dishes, and cold cuts were the top five contributors of sodium (5). In the current study, total caloric intake appeared to account for most of the differences in sodium intake; overall sodium density for the ≤1,500 mg/day and the <2,300 mg/day groups did not differ, although small but significant differences were found in a couple of subcategories (i.e., grain mixtures and breads).

The findings in this report are subject to at least four limitations. First, NHANES data are restricted to the noninstitutionalized population. Thus, the results from this study are not generalizable for residents of nursing homes, prisons, and other institutionalized populations. Second, calorie and sodium consumption estimates are based on self-reported intake data and thereby are subject to recall bias, misreporting of foods and portion sizes, and/or inaccurate or incomplete food composition tables, which can lead to underestimates of overall intake, but might not affect percentages. Third, the study did not account for sodium intake from salt added at the table or while cooking, and from medications and drinking water, resulting in underestimation of daily sodium intake and overestimation of the proportion of the population meeting dietary guidelines for sodium intake. Finally, availability of only two dietary recalls might overestimate variance in sodium and caloric intake and result in underestimation of the reported results.

Sodium intake largely comes from processed and restaurant foods. Some foods, such as cured meats or canned soups, are easily recognized as salty, but many other frequently consumed foods, such as breads and cookies, are not. Given the considerable overconsumption of sodium by most adults and the effect of sodium on blood pressure, policy and environmental changes are needed to reduce sodium intake across the U.S. population. In the United States, for example, a nationwide coalition led by New York City initiated discussions with food manufacturers to set voluntary benchmarks for lowering sodium content of specific food products. The first set of benchmarks was released in April 2010. Sixteen companies committed to meet at least one target.§ Also in April, the Institute of Medicine published recommendations for reducing sodium consumption (10), including a recommendation for mandatory national standards for the sodium content of foods, an interim strategy of voluntary action, and a series of supporting strategies, which includes ensuring and enhancing sodium-related monitoring.

References

1. Institute of Medicine. Dietary reference intakes for water, potassium, sodium, chloride, and sulfate. 1st ed. Washington, DC: The National Academies Press; 2004.
2. Bibbins-Domingo K, Chertow G, Coxson P, et al. Projected effect of dietary salt reductions on future cardiovascular disease. N Engl J Med 2010;362:590--9.
3. US Department of Health and Human Services, US Department of Agriculture. Dietary guidelines for Americans 2005. 6th ed. Washington, DC: US Department of Health and Human Services, US Department of Agriculture; 2005. Available at http://www.health.gov/dietaryguidelines/dga2005/document/pdf/dga2005.pdf. Accessed June 17, 2010.
4. CDC. Application of lower sodium intake recommendations to adults---United States, 1999--2006. MMWR 2009;58:281--3.
5. National Cancer Institute. Sources of sodium among the U.S. population, 2005--2006. Bethesda, MD: National Cancer Institute; 2010. Available at http://riskfactor.cancer.gov/diet/foodsources/sodium. Accessed June 14, 2010.
6. US Department of Agriculture. What we eat in America. Washington, DC: US Department of Agriculture; 2010. Available at http://www.ars.usda.gov/service/docs.htm?docid=15044. Accessed June 14, 2010.
7. Lloyd-Jones D, Adams R, Brown T, et al. Heart disease and stroke statistics---2010: a report from the American Heart Association. Circulation 2010;121:e1--170.
8. American Heart Association. Sodium (salt or sodium chloride). Dallas, TX: American Heart Association; 2010. Available at http://www.americanheart.org/presenter.jhtml?identifier=4708. Accessed June 14, 2010.
9. Mattes RD, Donnelly D. Relative contributions of dietary sodium sources. J Am Coll Nutr 1991;10:383--93.
10. Institute of Medicine. Strategies to reduce sodium intake in the United States. Washington, DC: The National Academies Press; 2010.

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