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J Clin Hypertens (Greenwich). 2010;12:793-799. © 2010 Wiley Periodicals, Inc.
Consuming high amounts of dietary sodium is associated with hypertension. The authors analyzed the HealthStyles 2005 and 2008 survey for behaviors to lower blood pressure related to dietary sodium, including the reduction of sodium intake and reading food labels for sodium content among hypertensives. All estimates were based on self-reported data. The relative percent change (RPC) in the prevalence of these behaviors between 2005 and 2008 was assessed. During the 3-year period, there were increases in the prevalence of reducing dietary sodium (RPC=17.2%, 56.6% in 2008 vs 48.3% in 2005; P<.05) and reading food labels for sodium content (RPC=7.9%, 53.0% vs 49.1%; P<.05). In 2005, the proportion of hypertensive adults who reported reducing dietary sodium was higher for persons 65 years and older, for blacks, for those with income <$25,000, and for those with more than a high school education compared with those in their comparison groups. In 2008, those aged 65 years and older had the highest percentage, while Hispanics and blacks had essentially the same percentage for reducing sodium. Based on 2005 and 2008 HealthStyles surveys, about half of hypertensive patients reported reducing their intake of sodium and reading food labels for salt. Health care providers should emphasize the importance of knowing the daily recommended limit for dietary sodium to help adults lower this intake.
An elevated intake of dietary sodium is strongly associated with hypertension.1–4 In 2005–2006, 29% of US adults were hypertensive and an additional 28% were prehypertensive.5 Consuming elevated levels of dietary sodium also increases the risk for cardiovascular disease and stroke, while reducing dietary sodium lowers blood pressure (BP) and reduces the risk of hypertension and cardiovascular events. A lifestyle of consuming fast foods, prepackaged foods, and frozen foods high in sodium leads Americans to consume substantially more salt than is recommended or needed. In the 2005 Dietary Guidelines for Americans,6 the US Department of Health and Human Services and the US Department of Agriculture recommended that adults consume <2300 mg of sodium per day but restrict themselves to ≤1500 mg/d if they are in specific high-risk populations (ie, hypertensive, middle-aged or older, or black). In fact, almost 70% of the US adult population is in one or more of these high-risk groups.7 According to reports from the National Health and Nutrition Examination Survey (NHANES), the mean daily sodium intake among adults aged 20 to 74 years in 2005–2006 was 3531 mg,8 far above the recommended level for the upper limit of sodium intake.
Using efficient strategies to monitor and reduce intake of dietary sodium is crucial for achieving Healthy People 2010 objectives 12.9 (reducing the proportion of adults with high BP), 12.10 (increasing the proportion of adults with high BP who have it under control), and 12.11 (increasing the proportion of adults with high BP who are taking action to help control it.9 Hypertension is not only a major risk for heart disease and stroke, the first- and third-leading causes of death in the United States,10 but it’s also a major risk factor for end-stage renal disease, peripheral vascular disease, and adult disability.4
Self-reported awareness of hypertension has been assessed in several studies,11–13 but few studies have analyzed actions taken to lower high BP, such as reducing intake of dietary sodium and reading food labels for sodium content.14 Our study uses the 2005 and 2008 HealthStyles surveys to assess: (1) the proportion of hypertensive adults who took action to reduce their sodium intake and read food labels, and (2) the relative percentage change from 2005 to 2008 in the proportion of adults who took sodium-related action to control their high BP.
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HealthStyles is one of three annual mail surveys administered to about 10,000 randomly selected households in the United States by Synovate, Inc, an international research organization. The survey is designed to collect data about health beliefs, attitudes, social norms, and behaviors surrounding important public health concerns such as receiving advice from physicians to control BP and actions taken to make specific modifications in lifestyle such as reduce sodium, lose weight, increase physical activity, and stop smoking. The samples of HealthStyles 2005 and 2008 were weighted for age, sex, race, income, and household size to represent the US census population.
Definition of the Study Measurements
Respondents were classified as having self-reported hypertension if they answered “yes” to the question “Have you ever been told on two or more different doctor visits that you had high BP?” and did not answer “yes” to the question “Was this only during pregnancy?” In 2005, of the adults with self-reported high BP, 152 (11%) had it during pregnancy and, in 2008, the figure was 129 (7%); these women were excluded from our analysis. Reducing intake of dietary sodium for hypertension was defined as “yes” if respondents answered “yes” to both “Has a doctor or other health professional ever advised you to cut down on salt or sodium in your diet to help lower your BP,” and “Are you now following this advice to cut down on salt/sodium?” (asked only if the answer to the first question was “yes”). Reading food labels for sodium content was defined as “yes” if respondents checked “usually” or “always” for the question “How often do you read food labels or the nutrition facts for serving amounts of sodium?”
Weighted frequency analyses provided information on the percentage of adults who had self-reported high BP with selected characteristics in 2005 and in 2008 by taking action to reduce sodium intake and reading food labels for sodium, respectively. Selected characteristics used in the analyses included sex, age (18–34, 35–44, 45–64, and ≥65 years), race/ethnicity (white, black, Hispanic, other), household income in thousands of dollars (<25, 25–39.9, 40–59.9, and ≥60), and education (less than high school graduate, high school graduate, some college, and college graduate or more). The chi-square test was performed to test differences, with an α level of 0.05 considered significant. Adjusted odds ratios (ORs) and 95% confidence intervals (95% CIs) were obtained from multivariate logistic models including two dependent variables: “took action to reduce sodium intake” and “read food labels for sodium.” Each model included 5 modifying variables: sex, age, race/ethnicity, household income, and education. All statistical analyses were performed with the statistical software package SAS, release 9.1 (SAS Institute, Cary, NC). Relative percent increase (RPI) with 95% CI was calculated to assess the changes in selected behaviors to improve BP among self-reported hypertensive adults between 2005 and 2008.
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In all, 6168 and 7000 eligible adults aged 18 years and older were mailed the HealthStyles survey in 2005 and 2008, respectively, of whom 4819 (78%) and 5399 (77%) responded by completing the survey. In both 2005 and 2008, 52% of respondents were women. When looking at middle-aged respondents in both survey years, there were more adults aged 45 to 64 years (32% in 2005 and 34% in 2008) than those aged 65 years or older (16% in both years).
Among adults with hypertension, the proportion who reduced sodium intake and read food labels for sodium content increased from 48.3% and 49.1% in 2005, to 56.6% and 53.0% in 2008, respectively (Figure 1). In both years, age group was directly associated with differences in the proportion who reduced sodium intake (P=.01 and P=.006, respectively) and read food labels for sodium content (P=.01 and .002, respectively) (Table I). Also in both years, a higher percentage of women read food labels than men (P=.045 and P<.0001, respectively). In 2005, blacks (63.9%) had the highest proportion among hypertensives of reducing dietary sodium intake, followed by Hispanics (56.8%), other groups (50.7%), and whites (43.7%) (P<.0001), while in 2008, Hispanics (64.1%) had the highest percentage followed by blacks (63.9%), whites (54.6%), and other groups (49.9%) (P=.03). In the first survey year (2005), those with the lowest household income had the highest percentage for reducing sodium intake (56.8%), followed by those with an income of $25,000 to $39,900 (51.6%), those with an income ≥$60,000 (43.2%), and those with an income of $40,000 to $59,900 (36.9%) (P=.0001). In 2008, the overall percentages of reporting reducing sodium intake were higher for each income level as compared with 2005, but differences among income groups were not significant.
Figure 1. Relative percent change in the proportion of persons with high blood pressure who engaged in selected behaviors to control blood pressure: HealthStyles, 2005 and 2008.
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Table I. Percentages of Hypertensive Adults Who Reported Specific Behaviors Regarding Their Sodium Intake: Healthstyles, 2005 and 2008
|Total||Reduced Dietary Sodium Intake||Read Food Labels for Sodium Content||Total||Reduced Intake of Dietary Sodium||Read Food Labels for Sodium Content|
|No.||No. (%)||P Value||No. (%)||P Value||No.||No. (%)||P Value||No. (%)||P Value|
|Overall||1277||636 (48.3)|| ||622 (49.1)|| ||1612||928 (56.6)|| ||877 (53.0)|| |
| Male||602||293 (48.4)||.99||269 (45.9)||.045||768||446 (56.6)||0.97||382 (47.1)||<.0001|
| Female||675||343 (48.3)||353 (52.3)||844||482 (56.5)||495 (59.6)|
| 18–34||101||40 (42.2)||.01||36 (44.0)||.01||90||33 (47.1)||0.006||38 (43.9)||.002|
| 35–44||219||86 (39.6)||84 (41.6)||181||86 (48.9)||80 (42.1)|
| 45–64||644||332 (48.9)||322 (48.3)||874||510 (57.5)||479 (54.8)|
| 65+||313||178 (54.4)||180 (56.3)||467||299 (63.5)||280 (59.8)|
| White||839||376 (43.7)||<.0001||386 (46.9)||.10||1097||598 (54.6)||0.03||565 (50.9)||.09|
| Black||223||144 (63.9)||118 (53.8)||252||168 (63.9)||151 (58.9)|
| Hispanic||143||78 (56.8)||82 (59.4)||159||108 (64.1)||92 (54.8)|
| Other||72||38 (50.7)||36 (47.5)||104||54 (49.9)||69 (63.2)|
|Household income, in thousands of dollars|
| Under 25||461||270 (56.8)||.0001||239 (52.7)||.32||509||309 (57.5)||0.18||291 (55.4)||.35|
| 25–39.9||198||104 (51.6)||97 (50.0)||204||108 (54.3)||107 (52.4)|
| 40k–59.9||177||68 (36.9)||75 (44.1)||260||168 (64.0)||145 (57.3)|
| 60+||441||194 (43.2)||211 (47.3)||639||343 (53.5)||334 (49.8)|
| <High school graduate||119||72 (59.6)||.035||58 (47.9)||.24||108||68 (59.6)||0.69||52 (50.0)||.33|
| High school graduate||360||184 (49.6)||164 (44.1)||450||271 (58.5)||224 (49.7)|
| Some college||434||217 (49.0)||220 (52.5)||586||331 (55.4)||350 (56.3)|
| College graduate or more||330||144 (42.7)||161 (48.8)||455||249 (54.7)||243 (52.2)|
Among the hypertensive patients, the RPI from 2005 to 2008 for reporting reducing dietary sodium was 17.2% (95% CI, 10.2%–29.0%) and for reading food labels for sodium content was 7.9% (95% CI, 5.0%–13.0%) (Figure 1). Among hypertensive patients who reduced dietary sodium in 2005 and those who did so in 2008, the percentage who also read food labels increased from 64.0% to 69.1%, respectively (RPI, 8.0%; 95% CI, 5.0%–12.8%) (Figure 2).
Figure 2. Relative percent change from 2005 to 2008 in reading food labels among hypertensive adults who reduced dietary sodium: HealthStyles, 2005 and 2008.
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Multiple logistic regression analyses show that the two youngest age groups (18–34 years and 35–44 years) were only about half as likely to reduce sodium intake or to read food labels as those aged 65 years and older in both 2005 and 2008 (Table II). The proportion of female respondents who read food labels was significantly higher than their male counterparts in 2008 but not in 2005. Additionally, the proportion of black and Hispanic hypertensive adults who reduced sodium intake was significantly higher than whites in 2005, but in 2008 only blacks had a significantly higher proportion than whites. In 2005, only Hispanics had a higher proportion who read food labels for sodium compared with whites, but there was no difference in 2008.
Table II. Adjusted Odds Ratios for Sodium-Reducing Behaviors Among Hypertensive Adults: 2005 and 2008
|Characteristic||Adjusted Odds Ratio (95% Confidence Interval)|
|Reduced Sodium Intake||Read Food Label for Sodium||Reduced Sodium Intake||Read Food Label for Sodium|
| 18–34||0.49 (0.27–0.87)a||0.54 (0.30–0.97)a||0.46 (0.24–0.89)a||0.47 (0.25–0.85)a|
| 35–44||0.51 (0.34–0.77)a||0.48 (0.32–0.72)a||0.48 (0.32–0.72)a||0.43 (0.28–0.64)a|
| 45–64||0.80 (0.58–1.09)||0.67 (0.49–0.91)a||0.77 (0.59–0.99)a||0.78 (0.61–1.01)|
| Female||0.86 (0.66–1.12)||1.31 (1.00–1.71)||0.97 (0.74–1.28)||1.68 (1.28–2.19)a|
| Black||2.32 (1.59–3.39)a||1.25 (0.87–1.80)||1.60 (1.12–2.29)a||1.35 (0.97–1.88)|
| Hispanic||1.70 (1.06–2.73)a||1.95 (1.22–3.11)a||1.44 (0.93–2.24)||1.38 (0.89–2.15)|
| Other||1.88 (1.08–3.28)a||1.14 (0.67–1.96)||0.78 (0.46–1.31)||1.53 (0.90–2.61)|
|Household income, in thousands of dollars|
| Under 25||1.44 (1.01–2.07)a||1.12 (0.78–1.61)||0.98 (0.70–1.38)||1.07 (0.77–1.48)|
| 25–39.9||1.23 (0.83–1.82)||1.02 (0.69–1.52)||0.86 (0.57–1.28)||1.07 (0.73–1.56)|
| 40–59.9||0.69 (0.45–1.05)||0.74 (0.49–1.11)||1.52 (0.95–2.42)||1.29 (0.84–2.00)|
| <High school graduate||1.32 (0.78–2.25)||0.71 (0.42–1.20)||1.11 (0.64–1.93)||0.72 (0.42–1.24)|
| High school graduate||1.16 (0.80–1.67)||0.71 (0.49–1.02)||1.09 (0.76–1.58)||0.76 (0.53–1.10)|
| Some college||1.16 (0.82–1.63)||1.05 (0.75–1.49)||1.04 (0.71–1.51)||1.15 (0.81–1.63)|
| College graduate or more||Reference||Reference||Reference||Reference|
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Reducing the intake of sodium in the diet is associated with reductions in BP. In addition, the Dietary Approaches to Stop Hypertension (DASH) diet is widely recommended by physicians to reduce BP among adults who have either hypertension or prehypertension.2,15–17 The DASH diet increased the amount of fresh fruit and vegetables consumed, which reduces the intake of processed foods and thus sodium intake. Lifestyle modifications to adequately reduce dietary sodium rely on reading food labels for sodium content. Per the present study, there appears to have been an improvement in the rate of behaviors to lower BP among hypertensive adults from 2005 to 2008, as indicated by the results reported in the present study for reducing dietary sodium intake and reading food labels for sodium content. Even so, the new estimates for reducing dietary sodium (57%) and reading food labels for sodium content (53%) remains insufficient for maximum public health impact.
The increase from 2005 to 2008 in reading food labels for sodium intake among hypertensive persons who took action to reduce their intake of sodium is encouraging, but the final percentage was just 69%. This is discouraging since all hypertensive patients should be actively reducing their sodium intake to the recommendation of ≤1500 mg/d for special groups (hypertensives, blacks, middle-aged adults). Reading labels for sodium content is paramount to successfully reduced sodium intake.6,8 Furthermore, it has been reported that the proportion of the population to whom this lower recommendation applies has increased within recent years, from 64% in 1999–2000 to 69% in 2005–2006 (per NHANES).7 This increase was generally reflected in the increased presence of special populations in the HealthStyles survey that we used. Health care professionals, community health workers, and public health agencies need to effectively inform the public about the recommended dietary intake of sodium and how to read food labels for sodium content when they are advising reduction. Providing information about reading food labels for sodium and the differences in sodium content between fresh fruits and vegetables and processed foods is important to include during counseling.
Risk factors for hypertension include excess body weight; excess intake of dietary sodium; inadequate physical activity; inadequate intake of fruits, vegetables, and potassium; smoking cessation; and excess intake of alcohol.4,15,16 Among population groups with hypertension, blacks have a higher prevalence, earlier onset, more severe outcomes, and more clinical sequelae than non-Hispanic whites.4 Mexican Americans have lower control rates than non-Hispanic whites and blacks.4 Sociodemographic factors such as education and income may affect people’s ability to buy fresh, low-sodium foods. Students in schools near fast-food businesses are less likely to consume low-sodium foods, a problem that is associated not only with obesity in our nation’s youth but also with increasing the likelihood of poor eating habits.17,18 Several studies have reported the benefits of reducing dietary sodium intake on hypertension or cardiovascular disease,1,2,16–20 and in the Trials of Hypertension Prevention (TOHP),1,18 even prehypertensive participants who reduced their sodium intake during the study period were 25% to 30% less likely to experience a cardiovascular event than were comparable participants with no restrictions on dietary sodium. Close communication with health care professionals should always include discussion of individually tailored health management, especially among high-risk individuals taking medications that increase the excretion of sodium.
The findings reported in this study should be viewed in light of several possible limitations. First, because HealthStyles is a mail survey, it reaches a sample population in which minority and low-income households may be underrepresented. Even so, the HealthStyles survey is based on a national sample and its findings correlate well with surveillance data from the Behavior Risk Factor Surveillance System of the Centers for Disease Control and Prevention. Second, because the survey requires literacy in the English language, some households would not be able to participate. Lastly, the self-reported data might not provide complete or accurate findings on intake of dietary sodium or advice received from a health care provider.
Conclusions/Public Health Impact
In 2008, based on self-reports, just over half of US adults with hypertension reported reducing their intake of dietary sodium or reading labels for sodium content. For the monitoring of sodium intake among those wishing to control their BP, emphasis should not be placed solely on reducing sodium intake but also on reading food labels for sodium content. Increased public education of reading food labels for sodium content cannot occur without also educating about the US Department of Agriculture’s recommendation of <2300 mg/d of sodium) for the general population but also about the restricted intake of ≤1500 mg/d for special populations. Knowing the recommended sodium intake per day is vital to be able to take proper action in reducing sodium intake and reading food labels. Additionally, more attention needs to be placed on the key high-risk populations (hypertensive persons or normotensive blacks and normotensive middle-aged and older adults) as well as on those with prehypertension. Strategies to increase the population’s proper ways to read food labels and their knowledge of the recommended sodium intake should also be developed and implemented to address gaps in knowledge between specific groups. Overall, US adults became more likely to decrease their dietary intake of sodium in 2008 than in 2005, but this behavior, as well as other behaviors to lower BP, needs to continue to increase to reduce the prevalence of hypertension and its associated outcomes in the United States.