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Dietary Responses to a Hypertension Diagnosis: Evidence from the National Health and Nutrition Examination Survey (NHANES) 2007–2010 a

Alexander N. Slade & Hyun Kim

a

a

University of Illinois at Urbana-Champaign Accepted author version posted online: 25 Jul 2013.Published online: 10 Feb 2014.

To cite this article: Alexander N. Slade & Hyun Kim (2014) Dietary Responses to a Hypertension Diagnosis: Evidence from the National Health and Nutrition Examination Survey (NHANES) 2007–2010, Behavioral Medicine, 40:1, 1-13, DOI: 10.1080/08964289.2013.826171 To link to this article: http://dx.doi.org/10.1080/08964289.2013.826171

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BEHAVIORAL MEDICINE, 40: 1–13, 2014 C Taylor & Francis Group, LLC Copyright  ISSN: 0896-4289 print/1940-4026 online DOI: 10.1080/08964289.2013.826171

Dietary Responses to a Hypertension Diagnosis: Evidence from the National Health and Nutrition Examination Survey (NHANES) 2007–2010 Alexander N. Slade and Hyun Kim

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University of Illinois at Urbana-Champaign

Dietary modification has been shown to substantially reduce blood pressure among people with hypertension. This article uses data from the 2007–2008 and 2009–2010 cross-sections of the National Health and Nutrition Examination Survey (NHANES) to examine the extent to which a hypertension diagnosis can influence individuals’ dietary choices. Several models were estimated to clarify the association of a hypertension diagnosis with dietary factors related to hypertension management. A comparison group of individuals at risk for developing hypertension was used. Results suggest that individuals who received a recent diagnosis of hypertension are more likely to have lower intakes of some dietary factors important in blood pressure management, including sodium. The results also highlight a discrepancy between added salt use and dietary sodium intake. While more recent hypertensive patients tended to consume lower levels of dietary sodium, patients diagnosed longer ago tended to use less added salt. Given that those diagnosed were more likely to have lower blood pressure profiles and improved diets, especially close to the time of diagnosis, the results of this study underscore the need for a prompt and accurate diagnosis of hypertension. Keywords: hypertension, dietary treatment, disease diagnosis, health investment, National Health and Nutrition Evaluation Survey

Heart disease, cancer, and stroke have been the leading causes of death in the United States from 1980 to 2009.1 Hypertension, or high blood pressure, is a major risk factor for heart disease and stroke, among other diseases. In fact, the World Health Organization recently identified hypertension as the single leading risk factor formortality worldwide.2 Approximately 73 million adults in the United States, or one out of every three adults, have high blood pressure, while another 59 million (one in four) adult Americans have prehypertension, or elevated blood pressure not high enough to be classified as hypertension, but high enough to increase the risk for developing hypertension.3 Like many other chronic health problems, the risk for and consequences of hypertension increase with age, making its management particularly important in older individuals.4 However, since hypertension is often substantially or completely asymptomatic, it is often undiagnosed or untreated in the general population.3,5 Correspondence should be addressed to Alexander N. Slade, University of Illinois College of Medicine at Urbana-Champaign, 125 Medical Sciences Building, 506 S. Mathews Avenue, Urbana, IL 61801. E-mail: [email protected]

If hypertension remains poorly controlled over a prolonged period of time, its complications are more likely to emerge throughout life. The long-term sequelae of hypertension can be severe, including heart and kidney disease, stroke, and blindness. A newly diagnosed hypertensive patient would typically be advised to adopt a healthful dietary regime, lower their sodium intake, and lose weight.6 Dietary modification is especially beneficial in the context of hypertension since these activities can reduce blood pressure both contemporaneously due to physiological changes (eg, sodium can directly increase blood pressure), as well as long-term, by promoting weight loss. Dietary and related lifestyle changes have long attracted attention as important modalities in the treatment of hypertension.7–10 Several specific dietary approaches have been studied in the context of mitigating hypertension, the most popular of which include the Dietary Approaches to Stop Hypertension (DASH) plan, the Mediterranean diet, and (especially lowcarbohydrate) variants thereof. Diets similar to the DASH diet, but substituting carbohydrates for either unsaturated fats or protein, have been studied and found to be efficacious

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in lowering blood pressure.11,12 A low-carbohydrate version of the Mediterranean diet, which substitutes carbohydrates with (mostly) unsaturated fatty acids has also been studied in the context of glycemic control and cardiovascular risk factors.13 Compared to the “typical” American diet, the DASH diet calls for a reduced intake of saturated fat, total fat, and cholesterol, and an increased intake of fiber and minerals, such as potassium, magnesium, and calcium.14 The Mediterranean diet calls for increases in the intake of plant-based foods, nuts, fish, and olive oil, among others, which offer higher levels of fiber, antioxidants, and favorable fatty acids (such as monounsaturated and omega-3 fatty acids).15 Unsaturated fatty acids, along with fiber and several minerals (including calcium, magnesium, and potassium), have been associated with lower systolic and diastolic blood pressure levels,16–18 part of the beneficial health effects of both the DASH and Mediterranean diets are believed to arise from changes in intake of these nutrients. Further, clinical trial evidence has established that the DASH diet can reduce blood pressure, holding total body weight constant.19,20 In addition to these lifestyle and dietary changes, anti-hypertensive oral medications can be very efficacious in the treatment of hypertension. Furthermore, new oral medications or combinations of medication are consistently being put forth which offer fewer side effects and improved blood pressure management for hypertensive patients. Despite the benefits of dietary and lifestyle modifications for hypertensive patients, adherence to these behaviors (which may create drastic changes for some individuals) proves to be a challenging task clinically.21–23 In fact, only 65% of diagnosed hypertensives report adhering to recommended treatment guidelines.24 Compliance may be further compromised by the possibility that medication may supplant a healthier diet and lifestyle, which is a frequent concern among clinicians.25 Research on the association between healthy habits and hypertension has focused primarily on the extent to which dietary and lifestyle behaviors can mitigate or exacerbate hypertension. Little research, if any, has investigated the association between information about hypertension and healthy behaviors or between anti-hypertensive medication and those behaviors. The objectives of this study are to examine whether a diagnosis of hypertension encourages better dietary health management activities. Likewise, we consider the role of medication on promoting these behaviors. Since hypertension is often less symptomatic with a slower, more insidious course than other chronic diseases, such as heart disease or diabetes, health management responses to hypertension have remained understudied. Several theoretical reasons suggest why hypertensive patients may change their behavior in response to their diagnosis. Grossman26 theorized that individuals gain utility from good health both directly through their enjoyment of better health, as well as indirectly through increases in available

time and resources. Further, individuals are endowed with a health stock that depreciates over time. Importantly, people can make health investments (such as diet modification and medication) to increase one’s health stock or decrease the rate of depreciation. This model would predict that individuals who know that they have hypertension are more likely to make health investments, such as diet or lifestyle modifications and medication use, compared to those who do not know of their condition. In addition, health investments lower not only the risk of hypertension but also the risk of many other chronic diseases and complications that are related to hypertension. This awareness can further increase the incentive for people to invest in their health through better lifestyle practices. While studies frequently rely on Grossman’s conceptual framework, empirical studies testing the theoretical predictions of Grossman’s model are somewhat mixed. Several of these empirical tests are reviewed by Zweifel, Breyer, and Kifmann.27 For instance, Grossman’s model predicts that medical care is an input to produce optimal health, suggesting that health status be positively correlated with medical care. In practice, however, a negative correlation is often seen. However, Grossman’s model also predicts that the demand for health decreases as one ages, which is frequently observed in the literature. Thaler and Shefrin28 theorize that individuals are often unable to realize that their current behaviors might have negative consequences in the future. Individuals often behave in a time-inconsistent manner, and many of these inconsistent behaviors can represent a conflict between shortterm actions and long-term goals. In support of Thaler and Shefrin’s theory, several studies have demonstrated the effectiveness of strategies in which individuals pre-commit to healthier choices before they are exposed to potentially unhealthy ones.29,30 Other theoretical evidence has suggested that unhealthy behaviors, when done so over a long period of time, may be rational in the sense that the present benefit exceeds the discounted costs.31 Becker and Murphy’s model suggests that complementarity between present and future consumption of a behavior, such as smoking or sodium consumption among hypertensives, can explain addiction to a good. Empirical evidence regarding smoking behavior generally supports the rational addiction model.32,33 Based on this model, hypertensives may be willing to change their behavior if they believed that the future prices of healthy foods would decline. Conversely, if the long-term prices of anti-hypertensive medication declined, current hypertensives might not be willing to modify their behavior as much. Empirical evidence suggests that individuals may change their behavior (at least somewhat) after a new disease diagnosis. For instance, using British Panel data, Clark and Etil´e found that health shocks, through the diagnosis of a new disease or a decline in self-reported health status, can lower an individual’s propensity to smoke.34 Longitudinal data from the Health and Retirement Study (HRS) have been used to show that the development of acute or chronic health

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DIETARY RESPONSES TO A HYPERTENSION DIAGNOSIS

problems was associated with a decreased likelihood of smoking.35,36 Slade, using data from the HRS, showed that a new diabetes diagnosis, especially involving medication, can bring about significant behavioral change including losing weight, abstaining from alcohol, quitting smoking, and increasing exercise, but these changes can sometimes be shortlived.37 Finally, it was found that compared to undiagnosed diabetics who are unaware of their condition, diagnosed diabetics tended to make healthier lifestyle choices, such as decreasing intakes of carbohydrates and sugar products, abstaining from alcohol, and engaging in a higher frequency of exercise.38 This article extends the literature on investment behaviors in response to health information. Most importantly, we consider the role of hypertension, which remains understudied compared to other medical conditions in the context of health information. Additionally, we consider a rich set of dietary behaviors that are important in the management of hypertension and the reduction of its long-term medical consequences. METHODS Data and Sample Inclusion This article focuses on dietary choices that people with hypertension make that can aid in their blood pressure management. We use two cross-sections from the National Health and Nutrition Examination Survey (NHANES),39 which were collected between 2007 and 2008, and between 2009 and 2010. The NHANES is a stratified, multistage probability sample of the civilian, non-institutionalized US population. The data include sections derived from personal interviews, physical examinations, and laboratory tests. Importantly, NHANES contains detailed information on respondents’ food and nutrient intake on two non-consecutive days as well as clinical measurements, including repeated blood pressure measurements. Data on demographic information, such as age, gender, ethnicity and education, were also collected. We included individuals who were 20 years of age or older, and who completed the examination where blood pressure measurements were taken, and who completed at least one dietary recall interview. In the 2007–2008 and 2009–2010 cross-sections, 5935 and 6218 individuals age twenty or higher, respectively, responded to the survey. Of the 12,153 combined respondents, 4150 were excluded because of missing data from either the demographic, questionnaire, dietary or laboratory components of the survey. Measures

Dietary Outcomes The NHANES include a dietary component, which is obtained through 24-hour dietary recall interviews. We use the

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average of the nutrient values in our analyses. These data contain detailed dietary information about the composition of the various macro- and micro-nutrients in the diet consumed by the respondent over the 24-hour period(s). In order to evaluate the dietary components most germane to the management of hypertension, total daily energy intake and intake of several nutrients were used: cholesterol, sodium, alcohol, saturated fat, protein, carbohydrates, and sugars (in aggregate). In addition, respondents were asked the extent to which they use added salt in their diets. In the dietary survey, respondents are asked what type of salt is usually added to their food at the table. Those who report that they usually use any type of salt product at the table are classified as having used “added salt.” We considered if an individual used any added salt as a separate outcome variable in our analysis. Finally, we considered specific nutrients that are important to the DASH diet (including calcium, magnesium, and potassium), and the Mediterranean diet (including fiber and unsaturated fatty acids).

Hypertension Measures and Other Explanatory Variables A diagnosis of hypertension is generally made if systolic pressure is 140 mm Hg or higher, or if diastolic pressure is 90 mm Hg or higher. Prehypertension is generally considered to be systolic blood pressure in the 120–139 mm Hg range, or diastolic pressure in the 80–89 mm Hg range. In the NHANES, individuals in the sample were asked if they have ever been diagnosed with hypertension, along with their age when they received the diagnosis. We are precluded from using previous cross-sections of NHANES because the question regarding when the hypertension diagnosis occurred was not asked in NHANES before the 2007–2008 cross-section. To construct our independent variables of interest, the age at diagnosis was subtracted from the respondent’s current age at the time of the survey interview to ascertain how long ago the hypertension diagnosis occurred. A series of dichotomous variables was used to indicate those who have received a hypertension diagnosis (a) 0–2, (b) 3–5, (c) 6–10, (d) 11–20, or (e) 21 or more years before the survey. There was an approximately equal distribution of hypertensive patients in each of the five groups. The number of individuals in each group ranged from 389 for those diagnosed ≥21 years before the survey to 485 for those diagnosed between 11 and 20 years before the survey. Our analysis also included information about antihypertensive medication status, which is only germane to those who have already been diagnosed with hypertension. From NHANES, individuals were asked if they have been prescribed medication for their hypertension, which constitutes the majority of hypertensive patients. The results were controlled for demographic information, including age, agesquared, gender, ethnicity, education, marital status, and income level. We also controlled for diagnoses of other diseases

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that are frequently comorbid with hypertension, including diabetes, heart disease, and stroke.

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Empirical Strategy Given that the analysis deals with the effect of a hypertension diagnosis, the comparison group for diagnosed hypertensives should not be all non-diagnosed individuals in the NHANES, as many individuals have little appreciable risk for developing hypertension. Rather, we created a comparison group to capture individuals who are at risk for being diagnosed with hypertension, but who remain undiagnosed. We included in this group people who have been diagnosed with pre-hypertension or “borderline” hypertension, along with all individuals who had a measured average systolic pressure of 120 mm Hg or above, or a measured average diastolic pressure of 80 mm Hg or above, rendering them either pre-hypertensive or hypertensive. Including those in the “at risk” group as well as those diagnosed with hypertension, our sample was comprised of 4587 combined individuals from the 2007–2008 and 2009–2010 cross-sections of NHANES. While it is possible that individuals who have been diagnosed with pre-hypertension (or borderline hypertension) may be provided with dietary advice from their health care provider, our analysis focused on the association of a hypertension diagnosis with dietary outcomes; thus, individuals who were diagnosed with pre-hypertension are at an elevated risk for receiving a hypertension diagnosis and therefore may be included in the comparison group. The general estimation strategy we followed was similar to that of Kahn,38 who estimates the effect of being diagnosed with diabetes and medication on similar outcome measures, including dietary intake and lifestyle habits. However, unlike Kahn, we were able to ascertain when the diagnosis occurred relative to the survey interview when the dietary and lifestyle outcomes variables were collected. Specifically, we estimated Ordinary Least Squares (OLS) models to ascertain the role of a hypertension diagnosis at different points in the past on current dietary intake patterns. A logit model was estimated to consider the role of a hypertension diagnosis on whether or not an individual added salt to his or her food. Sampling weights were also included in all models to correct for differential propensities of selection into the NHANES. The first-day dietary recall weights are used to weight the estimates. Each of the two cross-section waves is given equal weights in the final analysis. We also considered the density of the nutrients in the respondent’s diet (i.e., the intake of the mineral or nutrient per 1000 kcal). The density of the nutrient intake is an important measure to consider because it reflects the relative composition of the diet; individuals may attempt to decrease their aggregate intake, but do so in a manner that may not be optimal in the management of their blood pressure. The full results for the nutrient density analyses are available from the authors upon request.

RESULTS Table 1 presents summary statistics for individuals based on their hypertension diagnostic status. More than half of the respondents in the NHANES sample (age 20 or above) are classified as “at risk” for hypertension, suffering from either pre-hypertension or hypertension, but remaining undiagnosed. Compared to at-risk individuals, diagnosed hypertensives are more likely to be female and substantially older than at-risk individuals. Importantly, individuals who received a diagnosis of hypertension (Column 3) are more likely to engage in “healthier” dietary choices. Notably, diagnosed individuals tend to consume lower aggregate levels of sodium, cholesterol, alcohol, total energy, total fat, saturated fat, protein, carbohydrates, and sugar. Somewhat surprisingly, diagnosed hypertensives consumed a lower level of anti-hypertensive nutrients such as potassium, calcium, magnesium, and fiber compared to those at risk. However, the differences in the intake levels of anti-hypertensive nutrients between the two groups are smaller than the intake differences observed for the more “harmful” nutrients, such as saturated fat or sodium. There is also a significantly lower use of added salt among diagnosed hypertensives compared to at-risk individuals. Diagnosed hypertensives are also much more likely to suffer from comorbid conditions such as diabetes, heart disease, or stroke, compared to the comparison individuals. Overall, diagnosed hypertensives have improved blood pressure profiles (especially diastolic pressure) compared to at-risk individuals: individuals at risk for hypertension have an average blood pressure of about 129/75 mm Hg, compared to 129/70 mm Hg among diagnosed hypertensives. This may be partly due to the fact that the vast majority (87.5%) of diagnosed hypertensives takes anti-hypertensive medication. Both of these groups of individuals had higher blood pressure measurements than the general NHANES sample, which had a mean blood pressure of approximately 120/70 mm Hg. While the blood pressure readings of diagnosed hypertensives do suggest room for improved blood pressure control (especially systolic pressure), this contrast underscores the importance of the information that one suffers from hypertension, and the damage that is potentially being done before an individual is diagnosed. Figures 1 and 2 show the raw, unadjusted average blood pressure measurements and dietary outcomes for groups of hypertensive patients after they have been diagnosed with hypertension. Considering systolic and diastolic blood pressure over time since the original diagnosis (Figures 1a and 1b, respectively), there is relatively little change in systolic pressure after a diagnosis. However, there is an increase in systolic pressure among individuals diagnosed with hypertension 21 years or more before the survey compared to those at risk. With regard to diastolic pressure, there is an almost 10 mm Hg drop in those who have been diagnosed with the disease for 21 or more years compared to at-risk individuals.

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TABLE 1 Descriptive Statistics by Hypertension Status

Demographic characteristics Age ∗∗∗ Male ∗∗∗ Caucasian Black Hispanic Other race Highest grade: high school Highest grade: some college Highest grade: college or above Married ∗∗∗ Widowed ∗∗∗ Divorced or separated ∗∗ Live with a partner ∗∗∗ Income between $25,000 and $45,000 ∗ Income between $45,000 and $75,000 Income above $75,000 ∗∗∗ U.S. born Health characteristics Received a hypertension diagnosis 0–2 years before survey Received a hypertension diagnosis 3–5 years before survey Received a hypertension diagnosis 6–10 years before survey Received a hypertension diagnosis 11–20 years before survey Received a hypertension diagnosis 21 or more years before surve Currently taking anti-hypertensive medication Diagnosed with heart disease ∗∗∗ Diagnosed with stroke ∗∗∗ Diagnosed with diabetes ∗∗∗ Systolic blood pressure (mm Hg) Diastolic blood pressure (mm Hg) ∗∗∗ Dietary intake Total energy (kcal) ∗∗∗ Any added salt ∗∗∗ Sodium (mg) ∗∗∗ Cholesterol (mg) ∗∗∗ Alcohol (g) ∗∗∗ Total fat (g) ∗∗∗ Saturated fat (g) ∗∗∗ Mononunsaturated fatty acids (g) ∗∗∗ Polyunsaturated fatty acids (g) ∗∗∗ Protein (g) ∗∗∗ Carbohydrate (g) ∗∗∗ Sugar (g) ∗∗∗ Fiber (g) ∗ Potassium (mg) ∗∗ Calcium (mg) ∗ Magnesium (mg) ∗∗∗ Number of observations

(1) Entire NHANES sample

(2) At-risk, but undiagnosed

(3) Diagnosed with hypertension

45 (16) 48% 70% 11% 14% 5% 23% 31% 28% 54% 5% 13% 8% 27% 23% 36% 84%

47 (16) 60% 70% 10% 14% 5% 25% 32% 25% 56% 5% 13% 7% 27% 23% 36% 84%

58 (15) 48% 69% 15% 9% 5% 26% 32% 21% 61% 11% 15% 5% 31% 22% 28% 88%

4% 3% 4% 4% 3% 15% 2% 2% 6% 120 (16) 70 (12)

2% 1% 5% 129 (13) 75 (12)

21% 19% 21% 23% 16% 87% 8% 6% 20% 129 (19) 70 (15)

2129 (882) 72% 3533 (1575) 284 (195) 10 (23) 80 (41) 26 (15) 29 (16) 17 (10) 83 (36) 259 (113) 117 (71) 17 (9) 2729 (1132) 988 (541) 303 (133)

2242 (908) 73% 3665 (1597) 309 (213) 13 (26) 84 (42) 28 (15) 31 (16) 18 (10) 88 (38) 268 (116) 121 (72) 17 (9) 2829 (1136) 1004 (538) 312 (133)

1986 (798) 62% 3410 (1454) 277 (183) 9 (20) 76 (38) 25 (14) 27 (14) 17 (10) 79 (33) 238 (100) 107 (64) 16 (8) 2704 (1062) 949 (516) 290 (121)

8003

2851

1736

Notes: Stardard deviations in parentheses. Differences tested between the at-risk group and diagnosed hypertension group. A t-test is used for continuous variables, and a proportion test is used for dichotomous variables. The at-risk group comprises individuals undiagnosed with hypertension, but who suffer from either hypertension or pre-hypertension. ∗ p < 0.10. ∗∗ p < 0.05. ∗∗∗ p < 0.01.

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FIGURE 1 Blood pressure, added salt use, and sodium, cholesterol and alcohol intake after a hypertension diagnosis. Note. Vertical bars represent 95% confidence intervals of the mean. The “at risk” comparison group represents individuals who have not received a diagnosis of hypertension, but who suffer from prehypertension or hypertension. Significance stars represent differences from the “at risk” group. ∗ p < .10, ∗∗ p < .05, ∗∗∗ p < .01. (Color figure available online.)

Though there are variations in average systolic and diastolic pressure across individuals who have been diagnosed at different points in the past, the overall measurements suggest relatively good control. It should be noted that within the at-risk group, there are individuals who had clinical hy-

pertension (≥140 mm Hg systolic pressure or ≥90 mm Hg diastolic pressure), and thus could potentially benefit from a hypertension diagnosis to help enable them to control their blood pressure. The other plots in Figure 1 show the average of added salt use, as well as sodium, cholesterol and

FIGURE 2 Macronutrient intake after a hypertension diagnosis. Note. Vertical bars represent 95% confidence intervals of the mean. The “at risk” comparison group represents individuals who have not received a diagnosis of hypertension, but who suffer from prehypertension or hypertension. Significance stars represent differences from the “at risk” group. ∗ p < .10, ∗∗ p < .05, ∗∗∗ p < .01. (Color figure available online.)

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alcohol consumption (Figures 1c, 1d, 1e, and 1f, respectively). Importantly, recently diagnosed hypertensive patients (those diagnosed 0–2 years before the survey interview) tended to eat less of each of these dietary items compared to “at risk” individuals. While compliance with added salt, sodium and alcohol consumption remained strong among individuals who have lived for many years with a hypertension diagnosis, cholesterol consumption has wider fluctuations among groups of patients according to their time living with the disease, suggesting that some individuals may have difficulty lowering their cholesterol consumption over a prolonged period of time. Figure 2 shows plots of the consumption of total energy, as well as the major macronutrients that comprise energy intake. As with the outcomes shown in Figure 1, individuals with hypertension tended to have lower intakes of energy and the related macronutrients compared to comparison individuals. Further, for total energy and the non-fat macronutrients (ie, protein and carbohydrates), consumption continues to decline over time. For total fat and saturated fat consumption, there is very little increase in intake over time. For the outcomes in Figure 1 and 2 taken together, there is little evidence of recidivism in dietary or blood pressure compliance over time, in that diagnosed hypertensives consistently tend to eat lower levels of several prohypertensive nutrients in their diets and have lower diastolic pressure profiles as compared to individuals in the “at risk” group. Though there are decreases in the “harmful” nutrients among patients who have been diagnosed with hypertension for a prolonged period of time, they may not necessarily be accompanied by increases in more “beneficial” nutrients. Indeed, Figure 3 shows patterns of intake of anti-hypertensive items such as potassium, calcium, magnesium, fiber and unsaturated fatty acids. Interestingly, the patterns shown in Figure 3 are similar to those depicted in Figures 1 and 2, in that more recently diagnosed hypertensives consume a lower aggregate level of the nutrients compared to the at-risk group. However, it is important to note the upward trends in the intakes of these items among those who have been diagnosed with hypertension. This suggests that individuals who have been diagnosed with hypertension for a long period of time may be more willing to change the composition of their diets in ways that better manage blood pressure, rather than simply lowering aggregate intake. Dietary Choices: The Value of a Hypertension Diagnosis To evaluate the value of a hypertension diagnosis, we compared the dietary choices of several groups of diagnosed hypertensive individuals (according to the length of time since their diagnosis) with a comparison group of at-risk individuals, after controlling for the demographic and health characteristics shown in Table 1. Anti-hypertensive medication was

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also controlled for in these models. The estimation results for the effect of a hypertension diagnosis on several key dietary variables, including added salt use and sodium consumption, along with cholesterol and alcohol consumption, are reported in Table 2. Table 2 shows that a hypertension diagnosis played a significant role in explaining differentials in the consumption of certain dietary items that tend to contribute little to energy intake, but that can have important physiological effects on blood pressure. Column 1 considers results from a logit model which predicted if a respondent ever adds salt to food at the table (on a usual basis). Individuals who were diagnosed with hypertension, regardless of how long ago they were diagnosed, tended to be less likely to add salt to food at the table compared to individuals who were at-risk or undiagnosed with hypertension. The association appears greater for individuals who have known they have had the disease for a long period of time. Compared to individuals in the comparison group, those who were diagnosed with hypertension for 11–20 years were approximately 35% less likely to add any salt to food at the table, whereas those who were diagnosed over 20 years were almost half as likely to add any salt. Both of these Odds Ratios were significant at the 5% level. While the direction of the Odds Ratio tended toward a lower likelihood of adding salt for those who were more recently diagnosed (i.e., 10 years or less), they remained insignificant. Medication status had no significant association with the propensity to add salt. We can compare the observation that hypertensives who have been aware of their disease for a prolonged period of time respond more strongly by adding less salt to the OLS results for actual sodium consumption (reported in Column 2). In this model, as in the previous model, diagnosed hypertensives tended to have lower dietary sodium consumption than comparison individuals. However, individuals who were the most newly diagnosed (i.e., 5 years or less) tended to have the lowest rates of sodium consumption. These newly diagnosed individuals tended to consume approximately 300 fewer milligrams of sodium compared to the comparison group. Individuals who were diagnosed longer tended to have a smaller (and insignificant) reduction in their sodium consumption. Another important result from this model comes from the positive, significant association of anti-hypertension medication status on sodium of about 270 mg. As only those who are diagnosed with hypertension are eligible to receive medication, this positive (harmful) effect must be added to the diagnostic effect for those hypertensives who are taking medication. This implies that for individuals were diagnosed five years before the survey and who are taking medication, there is no net association of a hypertension diagnosis on sodium consumption. In fact, for individuals who were diagnosed for a long period of time and who took anti-hypertensive medication (which constitutes a majority of this group), there is likely a net positive association on sodium consumption, suggesting that these individuals have higher sodium consumption than

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FIGURE 3 Anti-hypertensive nutrient intake after a hypertension diagnosis. Note. Vertical bars represent 95% confidence intervals of the mean. The “at risk” comparison group represents individuals who have not received a diagnosis of hypertension, but who suffer from prehypertension or hypertension. Significance stars represent differences from the “at risk” group. ∗ p < .10, ∗∗ p < .05, ∗∗∗ p < .01. (Color figure available online.)

their counterparts in the comparison group. The results from this model also suggest that individuals taking medication may view their medication as a substitute for lowering sodium consumption, and therefore choose to increase their sodium consumption believing that the medication will nullify its effect on blood pressure. Several important demographic factors were associated with added salt use and sodium consumption that are not depicted in Table 2. Specifically, Black individuals are about 20% less likely to add salt and had an average of 315 fewer milligrams of aggregate sodium intake in their diets. While

age was positively correlated with both aggregate sodium intake and cholesterol intake (an extra 24 and 6 grams per year, on average, respectively), age-squared was negatively correlated with these outcomes (approximately 0.5 and 0.07 fewer milligrams per year-squared, respectively). Those who were born in the US consumed an average of 269 more milligrams of sodium. The other outcomes considered in Table 2, cholesterol and alcohol consumption, were largely unrelated to hypertension diagnostic status or medication use. However, those with a heart disease diagnosis consumed, on average, 24 fewer milligrams of cholesterol, while those

TABLE 2 The Role of a Hypertension Diagnosis on the Added Salt, Sodium, Cholesterol, and Alcohol Consumption

Received a hypertension diagnosis 0–2 years before survey Received a hypertension diagnosis 3–5 years before survey Received a hypertension diagnosis 6–10 years before survey Received a hypertension diagnosis 11–20 years before survey Received a hypertension diagnosis 21 or more years before survey Currently taking anti-hypertensive medication Number of observations R2

(1) Any added salt

(2) Sodium (mg)

(3) Cholesterol (mg)

(4) Alcohol (g)

0.74 (0.20) 0.69 (0.20) 0.79 (0.19) 0.65∗∗ (0.13) 0.52∗∗ (0.13) 0.95 (0.24) 4648

−286∗∗ (124) −302∗ (169) −159 (146) −126 (124) −57 (187) 270∗∗ (109) 4680 0.205

−27 (24) −12 (26) 17 (27) 15 (23) 8 (30) 6 (19) 4680 0.108

1 (2) 1 (3) 2 (3) 0 (3) 1 (4) −2 (3) 4680 0.080

Note: All models control for age, age2, gender, race, education, marital status, income, U.S. birth status, a interview period dummy, and diagnoses of heart disease, diabetes, and stroke. The reference group comprises individuals undiagnosed with hypertension, but who suffer from either hypertension or pre-hypertension. Odds ratios presented for the specification shown in Column 1. Standard errors in parentheses. ∗ p < 0.10. ∗∗ p < 0.05. ∗∗∗ p < 0.01.

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DIETARY RESPONSES TO A HYPERTENSION DIAGNOSIS

with a diabetes diagnosis consumed about 4 fewer grams of alcohol. In considering the density of aggregate sodium intake, individuals who were diagnosed between 11 and 20 years before the survey had a 100 mg/1000 kcal reduction in their sodium reduction. However, individuals taking antihypertensive medication (which constitutes a majority of hypertensive patients) had a 109 mg/1000 kcal increase in their sodium intake. Therefore, those diagnosed between 11–20 years before the survey who do not take medication seem to have the strongest decrease in the density of sodium intake in their diets. The association between a hypertension diagnosis and the density of cholesterol or alcohol intake was not statistically significant. Table 3 presents dietary outcomes that are related to energy intake. Specifically, we consider total energy consumed (column 1), as well as the major macronutrient components that comprise total energy intake: fat, protein, and carbohydrates (columns 2, 4, and 5, respectively). Specific kinds of these macronutrients are also of importance for the management of hypertension, namely saturated fats and aggregate sugar intake (columns 3 and 6, respectively) are considered, as well. In all models presented in Table 3, more recent patients tend to respond more and eat less of the respective nutrients than individuals who have lived longer with a hypertension diagnosis. Overall, there is a marginally significant, approximately 134 kcal decrease in total energy consumed by individuals who are very recently diagnosed with hypertension (two years or less before the dietary recall survey). Considering the potential macronutrients that are driving this energy reduction, total fat is highly significantly reduced in these patients, with individuals diagnosed with hypertension between 0 and 2 years before the survey consuming approximately 7 fewer grams of fat. There was also a sharp reduction in protein consumption among the most recently diagnosed group, with an approximately 7 gram reduction in daily protein consumption compared to individuals in the comparison group. Carbohydrate consumption was not significantly associated with hypertension diagnostic status, though the coefficients were negatively signed for more recently diagnosed individuals. In individuals diagnosed 0–2 years before the survey, saturated fat was marginally reduced, while sugar consumption was unaffected. It should be noted that significant associations for hypertension diagnoses on the outcomes presented in Table 3 were not seen in individuals who were diagnosed three or more years after the survey interview. In fact, the sign of the coefficients changed from negative (protective) to positive (harmful) for many of the dietary outcomes considered. Demographic and health variables that are associated with energy intake include gender (males consume a higher number of energy—about 630 kcal more than females—and higher levels of associated macronutrients), age (energy intake de-

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clines on average with age), and race (Black individuals tend to consume about 114 kcal less energy and fewer related macronutrients than Caucasians). In terms of how other diseases influence dietary behavior, diabetics tend to reduce their aggregate energy, carbohydrate, and sugar intakes by about 134 kcal, 27 g, and 24 g, respectively. Individuals with heart disease also report an average of 6 fewer grams of total fat consumption. There was no significant relationship between a hypertension diagnosis and the intake densities of any of the nutrients presented in Table 3. Finally, we considered specific nutrients that are important to the clinical efficacy of the DASH and Mediterranean diets in Table 4. Specifically, these nutrients include potassium, calcium and magnesium (which are especially important for the DASH diet), and unsaturated fatty acids and fiber (which are important components of the Mediterranean diet). From the results presented in Table 4, there is little evidence to suggest that hypertensive patients adhere to either of these dietary regimens. In fact, the results presented in Columns 5 and 6 suggest that hypertensive patients who were more recently diagnosed tended to eat 2 to 3 fewer grams of mono- or poly-unsaturated fatty acids, which are nutrients that can potentially lower blood pressure. Further, the intake density of polyunsaturated fatty acids decreased by 1 gram/1000 kcal among those diagnosed between 3 and 5 years before the survey. Additionally, those diagnosed between 11 and 20 years before the survey consumed 1 g/1000 kcal less fiber. Similarly, the results in Column 3 suggest that more recently diagnosed hypertensive patients consume marginally less magnesium compared to “at risk” individuals, forgoing a mineral that can potentially aid in their blood pressure management.

DISCUSSION Management of blood pressure can be difficult for many patients; even with medication, adherence to a proper dietary regime is an important component of the self-management of the disease. Our results are optimistic in the sense that groups of diagnosed hypertensives have dietary compositions more consistent with improved blood pressure management as they age with their disease. This is true of total energy intake, as well as several of the dietary macronutrients, such as fats and proteins. However, for the results considering sodium intake, there is a discrepancy between adding salt to food and actual consumption of sodium. The difference in the results reported in columns 1 and 2 of Table 2 present a contrast between an attempt to reduce sodium consumption (added salt to food at the table) and actual sodium consumption. The results of both models suggest that hypertensives may desire to reduce their sodium consumption; however, the results in column 2 suggest that

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SLADE AND KIM TABLE 3 The Role of a Hypertension Diagnosis on Energy Intake and Major Macronutrient Intake

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Received a hypertension diagnosis 0–2 years before survey Received a hypertension diagnosis 3–5 years before survey Received a hypertension diagnosis 6–10 years before survey Received a hypertension diagnosis 11–20 years before survey Received a hypertension diagnosis 21 or more years before survey Currently taking anti-hypertensive medication Number of observations R2

(1) Energy intake (kcal)

(2) Total fat (g)

(3) Saturated fat (g)

(4) Protein (g)

(5) Carbohydrates (g)

(6) Sugars (g)

−134∗ (73)

−7∗∗∗ (3)

−2∗ (1)

−7∗∗ (3)

−12 (11)

2 (8)

−84 (91)

−6 (4)

−1 (1)

−2 (4)

−7 (13)

4 (8)

−6 (84)

−2 (3)

−0 (2)

1 (4)

−1 (15)

2 (9)

45 (62)

2 (3)

1 (1)

2 (3)

5 (9)

8 (5)

20 (102)

0 (5)

0 (2)

−0 (4)

1 (14)

4 (7)

8 (70) 4680 0.229

3 (3) 4680 0.168

0 (1) 4680 0.154

2 (3) 4680 0.218

−3 (11) 4680 0.151

−7 (7) 4680 0.089

Note: All models control for age, age2, gender, race, education, marital status, income, U.S. birth status, a interview period dummy, and diagnoses of heart disease, diabetes, and stroke. The reference group comprises individuals undiagnosed with hypertension, but who suffer from either hypertension or pre-hypertension . Standard errors in parentheses. ∗ p < 0.10. ∗∗ p < 0.05. ∗∗∗ p < 0.01.

reducing the aggregate amount of sodium in the diet may be elusive for many patients. Additionally, more recently diagnosed patients may respond more by consuming less sodium than those diagnosed more distantly in the past. However, patients who have had the disease for a longer period of time

tend to add less salt to food at the table than more recent patients, suggesting that the mechanism by which more recent patients reduce their sodium consumption is likely not related to the addition of salt to food, but rather by avoiding sodium-rich foods and beverages.

TABLE 4 The Role of a Hypertension Diagnosis on Anti-hypertensive Nutrient Intake

Received a hypertension diagnosis 0–2 years before survey Received a hypertension diagnosis 3–5 years before survey Received a hypertension diagnosis 6–10 years before survey Received a hypertension diagnosis 11–20 years before survey Received a hypertension diagnosis 21 or more years before survey Currently taking anti-hypertensive medication Number of observations R2

(1) Potassium (mg)

(2) Calcium (mg)

(3) Magnesium (mg)

(4) Fiber (g)

(5) Monounsaturated fatty acids (g)

(6) Polyunsaturated fatty acids (g)

−129 (129)

−39 (68)

−20∗ (10)

−1 (1)

−3∗∗ (1)

−2∗∗∗ (1)

−76 (148)

9 (71)

−16 (15)

−2 (1)

−2 (1)

−2∗∗∗ (1)

1 (138)

61 (88)

1 (10)

−1 (1)

−1 (1)

−1 (1)

67 (150)

26 (65)

4 (12)

−1 (1)

1 (1)

0 (1)

20 (136)

58 (50)

−8 (12)

−1 (1)

0 (2)

−0 (1)

4 (122)

−46 (56)

1 (8)

1 (1)

1 (2)

1 (1)

4680 0.135

4680 0.109

4680 0.140

4680 0.097

4680 0.171

4680 0.100

Note: All models control for age, age2, gender, race, education, marital status, income, U.S. birth status, a interview period dummy, and diagnoses of heart disease, diabetes, and stroke. The reference group comprises individuals undiagnosed with hypertension, but who suffer from either hypertension or pre-hypertension. Standard errors in parentheses. ∗ p < 0.10. ∗∗ p < 0.05. ∗∗∗ p < 0.01.

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DIETARY RESPONSES TO A HYPERTENSION DIAGNOSIS

While there does appear to be a dietary response to a hypertension diagnosis that is generally favorable, the dietary changes may be indiscriminate, and are not necessarily optimal in terms of adherence to dietary therapy such as the DASH diet. Results from Table 4 suggest that hypertensives make few limited changes in their intakes of important minerals such as potassium, magnesium, and calcium, as well as fiber. Unsaturated fatty acid intake, which is a critical component to the Mediterranean diet, is actually decreased. However, the decreases in pro-hypertensive nutrients such as saturated fat and sodium presented in Table 3 suggest that while patients desire to make a change to help their condition, they may lack the education to implement more efficient dietary regimens to control their blood pressure. Additionally, some of the changes made may not have a clinically detectible influence on blood pressure. While patients who were diagnosed 21 years or more before the survey were about half as likely to add salt to their diet (a sizeable decrease), the largest estimate in the sodium intake reduction was approximately 300 milligrams per day among recently diagnosed (five years or less), non-medicated hypertensives. Using the estimates from a DASH diet study,20 a 300 mg reduction in sodium intake in this sample would translate into an approximately 1.5 mm Hg decrease in systolic pressure and a 0.75 mm Hg decrease in diastolic pressure, which are unlikely to be clinically significant. Perhaps more clinically important in this context are the reductions in total energy and pro-atherogenic nutrients such as saturated fat. Given that heart and vascular disease is an important complication of hypertension, reductions in saturated fat may help reduce the incidence or severity of vascular or heart disease in these patients. Lower energy intake can promote weight loss, which can further lower blood pressure and the risk of developing hypertensive complications. Overall, the observation that individuals respond to a hypertension diagnosis may present what Keenan refers to as a “window of opportunity” that disease information may be able to serve as an impetus for individuals to continually strive for better dietary and lifestyle habits. Furthermore, based on Figure 1, diagnosed hypertensives, on average, tended to have reasonably good blood pressure control, even many years after diagnosis, suggesting that the dietary habits (and medication) that they participate in may be sufficient to control blood pressure. Our results largely parallel those of Kahn,38 who performed a similar analysis, but considered the role of diabetes information using earlier versions of the NHANES. Kahn found that diagnosed diabetics tended be compliant with dietary factors implicated in glycemic control. Specifically, Kahn found that diagnosed diabetics tended to consume less energy, carbohydrates, sweets, and alcohol relative to undiagnosed diabetics. While carbohydrates and sugars are critically important for glycemic control among diabetics, these nutrients might not be as critical to the management of blood pressure in hypertensive patients, which may potentially ex-

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plain why we found little significance in these measures. Additionally, our results are similar to Slade,37 who found that diabetics tended to change unhealthy habits such as curbing drinking and increasing exercise initially, but individuals tend to revert back to poor habits and gain weight as time elapses since the initial diabetes diagnosis. However, in contrast to these two studies that found sharp declines in alcohol consumption subsequent to a diabetes diagnosis, we do not find that hypertensives tend to substantially modify their alcohol consumption.

CONCLUSIONS Hypertension is a common disease that remains a major risk factor for morbidity and mortality worldwide. There is a substantial fraction of hypertensives who are unaware of their condition, and many more who are “at risk” and suffer from pre-hypertension. Proper nutrition, as well as a healthy lifestyle, is essential to maintaining good health, especially among hypertensive individuals. This study analyzes how a hypertension diagnosis can affect dietary choices. The results show that compared to individuals who are either undiagnosed with hypertension, or at risk for developing the disease, diagnosed hypertensives tend to modify their diet by consuming less sodium and using less added salt. However, newly diagnosed hypertensive patients tend to respond more by consuming less sodium, whereas hypertension patients who have been diagnosed for a prolonged period to time tend to be less likely to add any salt to food at the table. This discrepancy highlights the contrast between desire to reduce sodium consumption and the true sodium consumed as part of the diet. Additionally, we find that newly diagnosed hypertensives (those receiving diagnoses 0–2 years before the survey) tend to decrease their consumption of total energy, protein, fats, and saturated fats. There is little evidence to suggest that changes in dietary intake patterns are associated with those recommended by popular dietary therapies for hypertension, including the DASH and Mediterranean diets. Notwithstanding some dietary non-compliance, diagnosed hypertensives tend to be in better control of their blood pressure (especially diastolic pressure) compared to undiagnosed and at-risk hypertensives. Understanding the role of information about one’s hypertension status in modifying diet can help policy makers reduce the number of individuals who are unaware of their hypertension status. The results of this study support this in two ways. First, diagnosed hypertensive individuals make healthier food choices than undiagnosed and “at risk” hypertensive individuals. Second, blood pressure control can be improved in those who are diagnosed compared to those who are undiagnosed. Thus, receiving a diagnosis of hypertension is essential to lowering the risk of chronic disease complications that can be caused by hypertension. This suggests that individuals (especially those “at risk” such as minorities and

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SLADE AND KIM

older individuals) can benefit from more frequent screenings for hypertension and other chronic diseases, and should be given rapid and accurate diagnoses by a health professional to better manage their health. If hypertensives modify their diet and lifestyle habits, they may be able to control their blood pressure without the need for medication, which may have both cost benefits and health benefits (to the extent that these medications carry side effects). This study has several limitations. The data come from self-reported data. Though the NHANES survey instrument attempts to minimize misreporting of food items, there is likely to be some discrepancy between the reported and actual dietary intake levels, most likely in the downward direction. Further, we used cross-sectional data from the NHANES. Future studies can benefit from the use of longitudinal data for hypertensive individuals. Rather than relying on reports of when a patient was diagnosed with hypertension, one would be able to follow hypertensive individuals after they are diagnosed, and observe how these individuals change their behaviors over time and whether their dietary habits improve (or decline) as individuals transition into and through hypertension status. The availability of this data would also enable more causal estimates because individual-level unobserved heterogeneity could be more easily isolated.

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