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Strategies to Reduce Sodium Intake in the United States 5 Sodium Intake Estimates for 2003–2006 and Description of Dietary Sources There is no question that Americans exceed the recommended levels of sodium intake by significant amounts. High intake levels are evident regardless of life stage, gender, race/ethnicity, and income. Further, estimated intake has trended upward when compared to the first National Health and Nutrition Examination Survey (NHANES) conducted in 1971–1974. Very little sodium occurs naturally in foods, and the majority of sodium in the U.S. diet is from sodium added during food processing and by restaurants and other foodservice operations such as cafeterias and catering services. Salt is the greatest contributor of sodium to the diet, but data are inadequate to quantify with any certainty the proportions attributable to sodium chloride (i.e., salt) compared to other dietary sources of sodium such as sodium bicarbonate, sodium benzoate, and sodium ascorbate. The 2005 Dietary Guidelines for Americans recommends that persons 2 or more years of age consume less than 2,300 mg of sodium per day (USDA/HHS, 2005). These recommendations further specify that many persons will benefit from further reductions in salt intake, including people with hypertension, African Americans, and middle- and older-aged adults (DGAC, 2005). The Centers for Disease Control and Prevention (CDC) recently reported that these special at-risk persons now constitute approximately 69 percent of the U.S. adult population (CDC, 2009). The Institute of Medicine (IOM) established reference values for so-
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Strategies to Reduce Sodium Intake in the United States dium for the first time in 2005 (IOM, 2005). An Adequate Intake1 (AI) was established by the IOM ranging from 1,000 to 1,500 mg for persons 2 or more years of age depending on age, and is a value that reflects the recommended average daily intake level based on observed or experimentally determined approximations or estimates of nutrient intake.2 The IOM also established a Tolerable Upper Level of Intake3 (UL) for sodium ranging from 1,500 to 2,300 mg depending upon age, which is the highest daily intake level that is likely to pose no risk of adverse health effects to almost all individuals in the general population (IOM, 2005). In setting the stage for the committee’s deliberations, Chapter 2 provides an overview of existing information about sodium intake in relation to evaluating the effectiveness of the major national public health initiatives. This chapter presents the results of analyses4 conducted for the committee’s study using data from NHANES,5 a large nationally representative survey conducted by CDC. Specifically, data from the 2003–2006 NHANES period were analyzed in order to specify current sodium intake. These dietary intake data are collected in the component of the NHANES known as What We Eat in America, but for the purposes of simplicity this chapter refers to them as NHANES data. The 2003–2006 NHANES data were also used to characterize current contributions to the diet based on food categories and to examine contributions to intake made by foods “from home” versus those “away from home.” Issues of monitoring and surveillance of intake and related factors are also considered. Background information on the NHANES and the methodologies used 1 Adequate Intake: IOM reference value: the recommended average daily intake level based on observed or experimentally determined approximations of estimates of nutrient intake by a group (or groups) of apparently healthy people that are assumed to be adequate (IOM, 2006). 2 The AI of 1,500 mg for adults 19 through 50 years of age was derived based on the following rationale: a diet that provides an average of 1,500 mg/day of sodium can meet recommended intakes of other nutrients; this level exceeds the levels of sodium intake that have been associated with adverse effects on blood lipid concentrations and insulin resistance, and this level allows for excess sodium loss in sweat by unacclimitized persons who are exposed to high temperatures or who are moderately physically active (IOM, 2005). The AIs for children and adolescents 1–18 years of age (1,000 mg/day for 1–3 years of age; 1,200 mg/day for 4–8 years of age; and 1,500 mg/day for 9–18 years of age) were extrapolated down from the AI for adults using the average of median energy intake levels of the age groups for adults and for children as the basis for extrapolation. The AI for adults 51 years and older (1,300 mg/day for 51–70 years of age and 1,200 mg/day for > 70 years of age) was extrapolated from younger individuals based on energy intake (IOM, 2005). 3 Tolerable Upper Intake Level: IOM reference value: the highest average daily nutrient intake level that is likely to pose no risk of adverse health effects to almost all individuals in the general population. As intake increases above the UL, the potential risk of adverse effects may increase. 4 Analytical support provided by Mathematica Policy Research, Washington, DC. 5 Available online: http://www.cdc.gov/nchs/nhanes.htm (accessed November 17, 2009).
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Strategies to Reduce Sodium Intake in the United States to analyze data for this study are described in Appendix E. Information from the analyses is summarized below, and more detailed data tables can be found in Appendix F. ESTIMATING SODIUM INTAKE Although data based on the “disappearance” of sodium in the food supply, as described in Chapter 2, can provide some information, two general methods of assessing the population’s intake of sodium are considered to provide reasonably accurate estimates: (1) dietary self-reports (interviews, food records, diaries, food frequency questionnaires of individuals) and (2) urinary sodium measures of individuals. The more accurate and reliable method of estimating sodium intake is the analysis of urine collected during a 24-hour period, which reflects about 90 percent or more of the ingested sodium (Clark and Mossholder, 1986; Luft et al., 1982; McCullough et al., 1991; Schachter et al., 1980). However, such measures are not currently included in national surveys carried out in the United States. Therefore, available information on the U.S. population’s sodium intake is based currently on national survey data derived from self-reported dietary intake of respondents. These large-scale national surveys provide representative estimates for the total population and large race/ethnic subgroups. However, NHANES data sets from 2003–2004 and 2005–2006 were combined for this study to provide larger sample sizes for subgroup analysis (see Appendix F). Clinical trials and smaller-scale studies can also provide dietary information for subgroups or special populations that cannot be gleaned from national surveys, but these cannot be relied upon to be representative. For population-level or group intake estimates, multiple 24-hour dietary recalls are the preferred method (IOM, 2000). Other methods are feasible, but require greater respondent effort and may alter behavior (e.g., food records and diaries) or overestimate food and energy intake (e.g., food frequency questionnaires) (Thompson and Subar, 2008). The strengths of the 24-hour dietary recall include the use of a standardized protocol to quantify the types and amounts of foods consumed over the course of a day, reduced respondent burden, and the provision of valid dietary intake estimates for groups and usual nutrient intake if two or more 24-hour recalls are collected for at least a subsample of the group. Also, individual intake data permit calculation of intake distributions for groups so that the prevalence of high and low intake can be estimated. Additionally, they reflect the sodium content of foods as consumed. The major limitation of any dietary intake method is that there is some degree of misreporting and measurement error (Thompson and Subar, 2008). For example, overweight persons may underreport intake, omitting certain foods or reducing the reported amounts; furthermore, parents may
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Strategies to Reduce Sodium Intake in the United States overreport their young children’s intake and be unable to estimate amounts accurately (Basch et al., 1990; Briefel et al., 1997; Devaney et al., 2004). Twenty-four hour recalls are also labor intensive to collect, and at least two non-consecutive days of data are needed to estimate usual intake. Over the years, improvements in methodologies have been made as part of the National Nutrition Monitoring and Related Research Program (Woteki, 2003), and the quality and validity of data from 24-hour recalls have been improved. Efforts have focused on training dietary interviewers to use standardized probes to elicit complete and accurate reports of intake, using appropriate measurement aids to help respondents report amounts, and developing statistical adjustments to allow better estimation of usual intake (Dwyer et al., 2003). Nonetheless, the intake estimates for sodium derived from NHANES are likely to underestimate the population’s true total intake. However, despite the inherent measurement errors in dietary data collection and the underestimation of true total intake of sodium by the population, these measures provide useful and relevant information. CURRENT SODIUM INTAKE OF THE U.S. POPULATION For the purposes of this study, intake data from the NHANES covering 2003–2006 (i.e., combination of the 2003–2004 and 2005–2006 surveys) were used and designated as “current.” For analyses related to quantitative sodium intake, estimates are provided as usual intake (see Appendix E); analyses related to food categories as well as non-food contributions to the diet are reported as 1-day means, as is sodium intake from earlier NHANES. As shown in Table 5-1, sources of dietary sodium include foods, salt added at the table, tap water, and dietary supplements. The sodium content of foods reflects salt added in cooking and food preparation. Methodologies for estimating table salt, tap water, and dietary supplements are described in Appendix E. Information on the contribution from medications was not available for the committee’s analysis. Drugs including anti-inflammatories, antacids, and laxatives can contribute to sodium intake.6 For example, sodium bicarbonate is often used to alleviate heartburn and acid indigestion.7,8 Although individuals with certain health conditions and their physicians may need to be concerned about the sodium content of some 6 Available online: http://www.megaheart.com/pdf/sodiuminmedications.pdf (accessed June 3, 2009). 7 Available online: http://www.medicinenet.com/sodium_bicarbonate-oral/article.htm (accessed November 11, 2009). 8 For example, commercial antacid tablets have 10 mg of sodium per two tablets (ingredient is sodium polyphosphate), according to the 2008 Nutrition Dietary System for Research database.
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Strategies to Reduce Sodium Intake in the United States TABLE 5-1 Mean 1-Day Sodium Intake from All Dietary Sources for Persons 2 or More Years of Age Dietary Source (mg/d) Total All Sources SE Fooda SE Table Saltb SE Tap Water SE Supplements SE All ages 2+ years 3,407 13.8 178 1.4 27 0.3 2 0.2 3,614 14.1 Children 2–5 years 2,388 26.4 33 1.5 9 0.3 1 0.1 2,432 26.6 6–18 yearsc 3,371 23.5 89 1.1 19 0.4 1 0.2 3,481 23.7 Adults Men, 19+ years 4,122 29.8 226 3.0 30 0.6 2 0.6 4,380 30.2 Women, 19+ yearsc 2,874 21.0 197 2.9 30 0.6 2 0.2 3,103 21.5 Total adults, 19+ yearsc 3,491 19.4 211 2.1 30 0.4 2 0.3 3,734 19.8 NOTES: Sodium intake from food is reported as a 1-day mean rather than usual intake to be consistent with reporting method for other dietary sources; d = day; mg = milligram; SE = standard error. aIncludes salt added in cooking and food preparation. bSalt added by the consumer at the table. cExcludes pregnant and lactating women; data for these persons are shown in Appendix F, Table F-1. SOURCE: NHANES 2003–2006. medicines (Szarfman et al., 1995; Ubeda et al., 2009), on a population level, medications overall contribute small amounts of sodium. The mean 1-day intake from all sources combined for persons 2 or more years of age during the 2003–2006 period is 3,614 mg/d, as shown in Table 5-1. The Dietary Guidelines for Americans recommends < 2,300 mg/d for this age group. Although recent data from 2009 are not available, indirect measures of estimating sodium intake (including trends in caloric intake, rates of obesity, observational studies, and the lack of consumer education) provide no indication that there is a decline in sodium intake since the 2003–2006 NHANES. Usual mean total sodium intake from all dietary sources (foods, table salt, tap water, dietary supplements9) increases with age from 2–3 years 9 Information on all prescription medicines and some over-the-counter medicines was collected in NHANES 2003–2006; however, no summary data on their sodium content were readily available for the committee’s analysis.
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Strategies to Reduce Sodium Intake in the United States FIGURE 5-1 Percentage contribution of dietary sources to total intake of sodium for persons 2 or more years of age. NOTES: Mean intake, 1 day, weighted 24-hour dietary recall data (n = 16,822); sodium intake from food is reported as a 1-day mean rather than usual intake to be consistent with the data available for other dietary sources. aIncludes salt added in cooking and food preparation. bSalt added by the consumer at the table. SOURCE: NHANES 2003–2006. through childhood and early adulthood, peaks at age 19–30 years, and then declines (Appendix F, Table F-1). On average, other dietary sources beyond foods provide an additional 207 mg/d of sodium, resulting in a mean total sodium intake of 3,614 mg for the population ages 2 years and older. More detailed information on mean intake and percentile distribution for usual intake is presented in Appendix F, Tables F-1 and F-2, respectively. Additional analyses reveal that the proportion of the population meeting the 2005 Dietary Guidelines for Americans recommendation of < 2,300 mg/d for sodium is only 10 percent (standard error [SE] = 0.5 percent); when only food sources are considered, 15 percent (SE = 0.6 percent) of the U.S. population ages 2 years and older meets the recommendation. Older women (71 years and older) are the most likely to meet the recommendation, but still only 36 percent (SE = 3 percent) consume < 2,300 mg/d. Foods contribute the vast majority of dietary sodium, estimated at 3,407 mg/d for persons 2 or more years of age for 2003–2006 (Appendix F, Table F-1). As shown in Figure 5-1, sources other than food contribute less than 6 percent of dietary sodium. For this reason, intake from food is discussed first.
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Strategies to Reduce Sodium Intake in the United States Intake from Foods By Age Usual mean daily sodium intake estimates from foods are about 2,200 mg at ages 2–3 years, peak at about 3,800 mg at ages 19–30 years, and decline slowly to about 2,600 mg above age 70 (see Figure 5-2 and Appendix F, Table F-5). Significant numbers within all age groups exceed the UL. Appendix F, Table F-3 contains more detailed information on usual intake percentile distributions for Dietary Reference Intake (DRI) age and gender subgroups. Median intake was compared to usual mean intake and found to be slightly lower, an average of 50–150 mg lower per day, but median intake tracks closely with mean intake (see Table 5-2 and Figure 5-2). More details on median values can be found in Appendix F, Table F-3. Usual mean sodium intake from foods exceeds the AI for all age groups, shown for children and adults in Figures 5-3 and 5-4, respectively. This indicates that there are no concerns about inadequate sodium intake in the U.S. population. Indeed, about 88 percent of Americans ages 2 years and older have excessive sodium intake from foods, that is, intake above the UL. As shown in Figure 5-5, sodium intake for a vast majority of people in all age groups exceeds the UL. Persons over 70 years are the largest percentage with intake below the UL; about one-third have usual sodium intake below the UL. FIGURE 5-2 Usual daily mean and median sodium intake from foods for persons 2 or more years of age. NOTE: d = day; mg = milligram. SOURCE: NHANES 2003–2006.
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Strategies to Reduce Sodium Intake in the United States TABLE 5-2 Usual Sodium Intake from Foodsa with Percentile Distributions for Persons 2 or More Years of Age Usual Intake Percentiles (mg/d) Excessive Intake 5th 10th 25th Median SE 75th 90th 95th % > UL SE All ages 2+ years 1,846 2,114 2,615 3,268 9 4,044 4,879 5,454 88 1 Children 2–5 years 1,455 1,619 1,922 2,311 16 2,767 3,250 3,579 87 2 6–18 yearsa 2,028 2,268 2,711 3,272 13 3,920 4,607 5,083 93 1 Adults Men, 19+ years 2,324 2,648 3,243 3,995 18 4,861 5,761 6,365 95 1 Women, 19+ yearsb 1,679 1,897 2,293 2,794 13 3,364 3,952 4,357 75 1 All adults, 19+ yearsb 1,845 2,126 2,654 3,344 13 4,166 5,048 5,652 86 1 NOTE: d = day; mg = milligram; SE = standard error; UL = Tolerable Upper Intake Level (see Appendix F, Table F-3). aIncludes salt added in cooking and food preparation. bExcludes pregnant and lactating women; data for these persons are shown in Appendix F, Table F-3 SOURCE: NHANES 2003–2006. FIGURE 5-3 Usual mean sodium intake from foods versus Adequate Intake (AI) for children. NOTE: d = day; mg = milligram. SOURCE: NHANES 2003–2006.
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Strategies to Reduce Sodium Intake in the United States FIGURE 5-4 Usual mean sodium intake from foods versus Adequate Intake (AI) for adults. NOTE: d = day; mg = milligram. SOURCE: NHANES 2003–2006. Sodium intake among children is often overlooked as a public health concern. Consistent with findings from NHANES 2003–2006, data from the Third School Nutrition and Dietary Assessment (SNDA-III) Study (Gordon and Fox, 2007), conducted in 2005 by Mathematica Policy Research and funded by the U.S. Department of Agriculture (USDA), show similar high intake estimates for school-age children. The SNDA-III data reveal a mean sodium intake from foods of 3,402 ± 46.4 mg among public school students on an average school day (Clark and Fox, 2009). Nearly 92 percent of all public school children (ages 6–18 years) were above the UL for sodium from food alone; this was highest among elementary school-age children (96 percent). Sodium intake for children younger than 2 years is not addressed by the Dietary Guidelines for Americans, but data collected and analyzed by Mathematica Policy Research for the 2002 Feeding Infants and Toddlers Study (FITS) indicate that high sodium intake begins early in life (Heird et al., 2006; Ziegler et al., 2006). Mean sodium intake, as estimated by this data set, exceeds the AI for infants ages 4–5 months (mean of 188 mg/d), infants 6–11 months (mean of 493 mg/d), and toddlers 12–24 months (mean of 1,638 mg/d) (Heird et al., 2006). Among toddlers, 58 percent exceed
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Strategies to Reduce Sodium Intake in the United States FIGURE 5-5 Percentage of persons 2 years of age or more exceeding the Tolerable Upper Intake Level (UL) for sodium from foods. SOURCE: NHANES 2003–2006. the UL for sodium. Preliminary findings from the 2008 FITS10 indicate that a large proportion of toddlers and preschoolers continue to have sodium intake above the UL. By Gender Beginning with the school-age period, boys have higher sodium intake than girls, a pattern consistent with higher energy intake (see Figure 5-6). Among older children and adults, women over 70 years have the lowest mean sodium intake (2,398 mg/d)—only preschoolers are lower. At each age group, the higher usual sodium intake by men is associated with a greater percentage with intake above the UL compared to women. Nine out of 10 adult men have excessive sodium intake. By Sodium Intake Density Sodium intake increases with increased calorie intake (Loria et al., 2001). As shown in Table 5-3, analyses for age and gender groups using 10 Nestle Nutrition Institute, presented at American Dietetic Association, Food & Nutrition Conference and Expo, Denver, CO, October 2009. Available online: http://www.foodnavigator-usa.com/Science-Nutrition/Preschoolers-diets-mimic-unhealthy-adult-eating (accessed November 9, 2009).
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Strategies to Reduce Sodium Intake in the United States FIGURE 5-6 Usual daily mean sodium intake from foods by gender. NOTES: d = day; mg = milligram; excludes pregnant and lactating women; data for these persons are shown in Appendix F, Table F-3. SOURCE: NHANES 2003–2006. NHANES 2003–2004 indicate correlation values for calories-to-sodium intake greater than 0.70 for most groups. Expressing sodium intake per 1,000 calories—sodium intake density—allows comparison of intakes without confounding related to associations between total calorie intake and total sodium intake. Appendix F (Table F-4) gives specific information for sodium intake density measures based on NHANES 2003–2006 for the DRI age and gender groups. Overall, other than children ages 2–8 years, sodium intake density values are quite similar, suggesting that many of the differences in sodium intake are a reflection of differences in calorie intake. Both men and women ages 50–71 years show the highest sodium intake density, while among adults, women 51–70 years of age show the highest sodium intake density. As would be expected, higher energy requirements are associated with higher sodium intake. Sodium intake density is considered relative to time trends in a later section. Intake from Foods for Subpopulations of Interest Race/Ethnicity As shown in Table 5-4, sodium intake levels are high among all racial/ethnic groups.
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Strategies to Reduce Sodium Intake in the United States TABLE 5-7 Top Five Food Contributors to Sodium Intake Within Food Categories for Persons 2 or More Years of Age Food Group Food Item Percentage of Sodium Contributed in Food Groupa Mixed dishes = 44% of total daily sodium Sandwiches (excluding burgers) 35.3 Pizza with meat 12.2 Hamburgers/cheeseburgers 8.5 Mexican entrées 6.9 Pasta dishes, Italian style 6.5 Sum 69.4 Meat, meat alternates = 15.5% of total Chicken 25.0 Cheese 15.3 Eggs 12.1 Bacon/sausage 10.6 Beef 7.7 Sum 70.7 Grains = 11.4% of total Bread 21.5 Cold cereal 18.5 Rice 10.9 Pancakes, waffles, French toast 9.6 Crackers 9.0 Sum 69.5 Vegetables = 9.3% of total Salad (greens)b 30.0 Cooked potatoes, not fried 16.7 Cooked potatoes, fried 15.2 Cooked tomatoes 9.2 Cooked green beans 4.3 Sum 75.4 Sweets = 5.0% of total Cookies 22.0 Cake/cupcakes 21.6 Ice cream 10.5 Pies/cobblers 9.3 Doughnuts 7.8 Sum 71.2 Condiments, oils, fats = 4.3% of total Catsup, mustard, relish, soy sauce 39.9 Gravy 12.3 Salad dressing 11.7 Garnishes such as pickles or olives 10.6 Margarine 7.4 Sum 81.9 Salty snacks = 3.4% of total Corn-based salty snacks 32.1 Popcorn 25.9 Potato chips 23.0 Pretzels/party mix 19.1 Sum 100.0
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Strategies to Reduce Sodium Intake in the United States Food Group Food Item Percentage of Sodium Contributed in Food Groupa Milk = 2.9% of total Unflavored 2% milk 28.8 Unflavored whole milk 19.2 Unflavored skim milk 12.9 Unflavored 1% milk 9.9 Yogurt 5.8 Sum 76.6 Beverages = 2.2% of total Noncarbonated sweetened drink 28.0 Regular soda 25.2 Sugar-free soda 12.8 Coffee 11.7 Beer 7.3 Sum 85.0 Beans, nuts, and seeds = 2.1% of total Baked or refried beans 37.6 Nuts 18.7 Beans 16.8 Protein or meal enhancement 12.4 Peanut or almond butter 6.9 Sum 92.4 Fruit = 0.1% of total Citrus juice 25.8 Non-citrus juice 24.5 Avocado, guacamole 13.8 Fresh melon 12.4 Other fresh fruit 4.5 Sum 81.0 aPercentage shown within each major category reflects the percentage of sodium contributed by that food item within the food category (e.g., sandwiches provide 35% of the sodium in the mixed dish category). bIncludes additions to salads such as salad dressing, cheese, meat, croutons, and other condiments. SOURCE: NHANES 2003–2006. comparisons of relative intake from different food supply sources are best expressed on the basis of sodium intake density, specifically as milligrams per 1,000 calories consumed. Currently, as shown in Table 5-9, mean sodium intake density is lowest for foods consumed at home (obtained at the store and prepared or consumed at home) and highest for foods consumed away from home, notably from restaurants and fast food establishments (as defined by NHANES). As discussed in Chapter 2, data collected between 1987 and 1995 (Lin et al., 1999) reveal sodium intake density measures for foods consumed at home to be similar to those from away-from-home sources (see Figure 2-4).
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Strategies to Reduce Sodium Intake in the United States TABLE 5-8 Sources of Sodium in Sandwiches and Hamburgers/Cheeseburgers by Percentage of Item for Persons 2 or More Years of Age Sandwiches (Excluding Burgers) Contribution to Total Sodium in Sandwich (%) Hamburgers/Cheeseburgers Contribution to Total Sodium in Hamburger (%) Cold cuts 23.9 Ground beef 36.7 Bread 19.2 Rolls 19.6 Cheese 11.2 Cheese 18.8 Hot dogs 9.2 Catsup, mustard, relish, etc. 8.1 Rolls 7.3 Garnishes such as pickles, olives 6.4 Bacon/sausage 4.1 Bread 4.9 Catsup, mustard, relish, etc. 2.7 Mayonnaise 1.8 Chicken 2.4 Bacon/sausage 1.7 Fish 2.3 Cooked tomatoes 0.5 Ham 1.8 Salad dressing 0.4 SOURCE: NHANES 2003–2006. Likewise, foods eaten at fast food restaurants and schools for that period show sodium densities similar to those classified as eaten at home, suggesting generally similar salt additions to foods in most food preparation and manufacturing locations, or similar food coding rules. The more recent data from NHANES 2003–2006 (see Table 5-9 and also Figure 2-4) reveal greater differences in the sodium intake density of foods obtained from the store (and prepared or eaten at home) versus all away-from-home sources. This suggests that within the U.S. food supply, away-from-home food sources are richer in sodium than foods consumed at home. Further, in the past two decades, the sodium intake density increased the most for fast food restaurants (see Figure 2-4). FIGURE 5-9 Percentage of sodium intake from home and away-from-home foods. SOURCE: NHANES 2003–2006.
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Strategies to Reduce Sodium Intake in the United States TABLE 5-9 Sodium Density for Foods from Home and Away for Persons 2 or More Years of Age Source of Food Sodium Density (mg/1,000 kcal) Home 1,422 Away (total) 1,825 Restaurants 1,925 Fast food/pizza restaurants 1,805 School 1,629 Other 1,466 NOTE: “Home” includes foods purchased at the store and prepared at home; “restaurants” includes those with waiters/waitresses and bar/tavern/lounge restaurants; and “other” includes foods from child or adult care centers, soup kitchens, Meals on Wheels, community food programs, vending machines, food gifts, mail order purchases, street vendors, etc. kcal = calorie; mg = milligram. SOURCE: NHANES 2003–2006. Other Approaches to Characterizing the Sodium Content of the Food Supply Other approaches can be used to describe the sodium content of the food supply beyond examining the main contributors of sodium to the diet on the bases of food category and types of eating establishments. However, as a general matter, the food supply as a whole has not been systematically tracked or monitored through surveys designed for this purpose. Alternatively, the sodium content of the food supply can be described using salt disappearance data (which can also be used to derive gross estimates of sodium intake). So-called “market basket” studies, such as the survey conducted by the Food and Drug Administration (FDA), could also be useful, although currently it is designed primarily for other purposes. The national databases related to food composition—which include sodium content and are maintained by USDA—cannot themselves characterize the sodium content of the food supply, but are instead a key component of the process of estimating sodium intake based on dietary recalls from a nationally representative sample of the U.S. population. However, selective comparisons of changes in food composition over time within these databases could provide some useful trend data on changes in sodium in the food supply. The only available study of this type did not include information on sodium (Ahuja et al., 2006). Salt Disappearance Data Monitoring intake from disappearance data allows for a reasonably accurate estimate of time trend patterns because common methods of collecting and accounting for use have remained similar over time. Salt disap-
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Strategies to Reduce Sodium Intake in the United States pearance data can be used to estimate time trend patterns in the availability of sodium for human consumption, with the understanding that there are losses and wastage that cannot be accounted for. As described in Chapter 2, the annual per capita salt disappearance data show a steady increase in per capita availability between 1983 and 1998. While this does not definitively indicate that there has been an increase in the overall sodium content of the food supply, it is suggestive. More recently, values appear to be leveling off or decreasing slightly. The peak levels in 1998 indicate that approximately 5,700 mg of sodium were available per person per day. Although the pattern of use over time suggests that early educational and program initiatives (such as in the early 1980s) were associated with a reduction in salt use, subsequent programs, including the implementation of a mandatory declaration of sodium content on all food labels in 1993 and multiple calls for food processors and food service operators to reduce the sodium content of foods since 1969, appear to have had little or no impact on salt availability for human use. Market Basket Study: FDA’s Total Diet Study The Total Diet Study (TDS) is an ongoing FDA program that determines levels of various contaminants and nutrients in foods.15 From this information, dietary intake of those substances by the U.S. population can be estimated. Since its inception in 1961 as a program to monitor radioactive contamination of foods, the TDS has expanded to include pesticide residues, industrial chemicals, and toxic and nutrient elements. The TDS involves purchasing samples of food throughout the United States, preparing the foods as they would be consumed (table-ready), and analyzing the foods to measure the levels of select contaminants and nutrients. Dietary intake of these substances by the U.S. population is then calculated by multiplying the levels found in TDS foods by the average consumption amounts for each food. The outcomes for sodium are reported as milligrams per kilogram of food. The number of different foods sampled in the TDS has increased from 82 food items when the study was initiated in the early 1960s to about 280 foods in the current program. Sample collections (also referred to as market baskets) are generally conducted four times each year, once in each of four geographic regions of the country (West, North Central, South, and Northeast). Food samples are purchased by FDA personnel from supermarkets, grocery stores, and fast food restaurants in three cities in each region and are shipped to a central FDA laboratory. 15 Available online: http://www.fda.gov/Food/FoodSafety/FoodContaminantsAdulteration/TotalDietStudy/default.htm (accessed November 18, 2009).
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Strategies to Reduce Sodium Intake in the United States The TDS analyzes sodium on composites, reports these as milligrams per kilogram of food, and does not convert the results for composites back to representative diets, thereby limiting the utility of the data on sodium relative to the food supply. Further, it is unclear whether the sampling scheme, food preparation, and documentation of product samples are sufficient or appropriate for sodium. For example, issues related to the proportioning of the sampling of vegetables among fresh, frozen, and canned may require a different approach for sodium (which should be based on how consumers consume them), given that the current focus is on contaminants and pesticides. National Food Composition Databases In theory, national food composition databases offer the opportunity to monitor changes in the sodium content of the food supply, but interpretation of such data is problematic. There can be a confounding effect due to improvements in the food composition data and changes in the approaches used to determine the listings for the sodium values of foods. Currently, about 70 percent of the sodium values in the food composition database used to code and assess sodium in NHANES 2003–2006 are analytical values, 5 percent are from food labels, 11 percent from manufacturers, and 15 percent imputed. Moreover, during the time dietary trends have been measured, the food composition database has been updated and expanded to include more brand names and fast food items as well as a few other restaurant foods.16 Maintaining an up-to-date database on the sodium content of foods is a challenging but essential task. Ahuja et al. (2006) examined the effect of improved food composition data on intake estimates in the United States through a reanalysis of data using multiyear versions of the tables of food composition. Sodium was not included in their analysis, but for the more than 25 nutrients and food components examined, results showed minor but statistically significant differences in mean intake estimates for most nutrients. MONITORING Monitoring intake of sodium and describing the nature of sodium sources in the food supply is fundamental to implementing and sustaining strategies to reduce sodium intake. While estimates of sodium intake based on dietary recall methodologies are useful and readily reveal the high intake levels among the U.S. population, more accurate methods for estimating intake are available, including the 24-hour urine sample. 16 Personal communication, J. Holden, USDA, Washington, DC, September 11, 2009.
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Strategies to Reduce Sodium Intake in the United States The collection of 24-hour urine specimens to assess sodium intake reflects the gold standard for estimating sodium intake, however this method has not been included in the NHANES because of the complexity and cost of such collections. NHANES has collected “casual” urine specimens to assess environmental analytes, determine the possibility of pregnancy, and measure kidney function and iodine status.17 However, these have not been analyzed for sodium, and it is recognized that casual specimens are not likely to provide a desirable level of accuracy for the purposes of estimating intake. Nonetheless, because surplus collections of these samples have been stored since NHANES became a continuous survey in 1999, these samples offer the opportunity to carry out pilot studies relative to comparisons, given that NHANES plans to collect a second urine specimen as part of the recently initiated 2009–2010 survey. All of the usual improvements frequently called for relative to estimating intake through dietary recall methods also apply to sodium. These include advances in recall methods and probing techniques, enhancement of food composition tables for sodium content of foods, and timely, userfriendly releases of data. More frequent analysis and reporting of distributions of usual sodium intake (and energy for calculations of sodium density) and food sources of sodium are warranted to better monitor sodium intake and initiatives to reduce sodium. Of particular importance in the case of sodium for food composition tables is the ability to incorporate into such tables the sodium content of menu items offered by the major chain restaurant/foodservice operations. Finally, there is considerable utility to be gained through the implementation of appropriate market basket studies and innovative approaches to characterizing the sodium content of the food supply. The committee considered these in more depth as described in Chapter 8. REFERENCES Ahuja, J. K. C., J. D. Goldman, and B. P. Perloff. 2006. The effect of improved food composition data on intake estimates in the United States of America. Journal of Food Composition and Analysis 19(Supplement):S7-S13. Azoulay, A., P. Garzon, and M. J. Eisenberg. 2001. Comparison of the mineral content of tap water and bottled waters. Journal of General Internal Medicine 16(3):168-175. Basch, C. E., S. Shea, R. Arliss, I. R. Contento, J. Rips, B. Gutin, M. Irigoyen, and P. Zybert. 1990. Validation of mothers’ reports of dietary intake by four to seven year-old children. American Journal of Public Health 80(11):1314-1317. Bradshaw, M. H., and G. M. Powell. 2002. Sodium in drinking water. Manhattan, KS: Kansas State University Agricultural Experiment Station and Cooperative Extension Service. 17 Available online: http://www.cdc.gov/nchs/nhanes/nhanes_questionnaires.htm (accessed November 18, 2009).
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