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Department of Medicine, Division of Geriatrics, Palmetto Health Alliance/University of South Carolina, Columbia, SC 29203 and * Medical College of Wisconsin, Milwaukee, WI 53226
1To whom correspondence should be addressed. E-mail: ihab.hajjar{at}palmettohealth.org.
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ABSTRACT |
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 TOP ABSTRACT METHODSRESULTSDISCUSSIONLITERATURE CITED |
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KEY WORDS: • diet • blood pressure • south • geographic comparisons • NHANES-III
Observational studies across populations convincingly demonstrate an association between blood pressure level and nutrient consumption (1
–4
). Among studies, blood pressure is consistently related to dietary NaCl and alcohol consumption and inversely related to dietary potassium, calcium and magnesium (2
,3
). Within populations, however, it has been difficult to detect a direct correlation between blood pressure level and electrolyte intake, both because of the constricted range of electrolyte consumption within a population and because of the difficulty of estimating electrolyte consumption (5
). Results of clinical trials also document an effect of NaCl on blood pressure and more modest and less consistent effects of potassium, calcium or magnesium supplements (1
–3
,6
–8
). In cross-sectional population-based studies, age-related increases in blood pressure are augmented by NaCl consumption and attenuated by calcium intake (9
,10
). Population studies suggest that blood pressure is also related to the consumption of several macronutrients. Specifically there is limited and inconsistent evidence suggesting that blood pressure is inversely associated with dietary protein and positively associated with dietary cholesterol, saturated fatty acids and starch (1
,11
,12
).
For many decades, the southeastern region of the United States has had the highest stroke mortality rates in the country (13
–17
). This region has also had higher mortality rates from myocardial infarction, heart failure and end-stage renal disease than other regions (18
–20
). This may be due to the higher prevalence of hypertension and the somewhat lower rate of hypertension control, especially in males, in this area (21
). In addition, compared with other regions in the United States, hypertensive patients in the southeast have more severe disease (22
,23
) and are less responsive to antihypertensive agents (24
). The reason for these geographic differences is not well understood and is likely to be multifactorial. Variations of dietary intake among the different U.S. regions may explain some of this geographic variability.
We designed this analysis to describe regional variations in blood pressure and the reported consumptions of nutrients, focusing on those linked to blood pressure, in the United States based on data obtained from the National Health and Nutritional Examination Survey III (NHANES-III).2
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METHODS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONLITERATURE CITED |
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). We obtained data on all individuals 18 y or older. Information collected included age, gender, ethnicity, weight, height, blood pressure and dietary intake. Diet information was obtained with a 24-h questionnaire. We included both dietary factors that have been linked to blood pressure and additional factors for descriptive reasons. Therefore for our analysis we used data on macronutrients (protein, carbohydrates, total fatty acids, saturated fatty acids, monounsaturated fatty acids, polyunsaturated fatty acids, cholesterol and fiber), micronutrients (sodium, potassium, calcium, magnesium, zinc, copper and iron), vitamins (C, E, riboflavin, B-6, B-12, niacin and thiamin) and alcohol. In addition, daily energy consumption and frequency of "adding salt to food on the table" data were obtained. Regional classification for each participant was also obtained. NHANES-III divided the United States into four regions: northeast (Maine, North Hampshire, Vermont, Connecticut, Massachusetts, Rhode Island, New Jersey, New York and Pennsylvania), midwest (Ohio, Indiana, Michigan, Illinois, Wisconsin, Missouri, Iowa, Minnesota, Kansas, South Dakota, North Dakota and Nebraska), south (Delaware, Maryland, District of Columbia, West Virginia, Virginia, Kentucky, Tennessee, North Carolina, South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, Oklahoma, Arkansas and Texas) and west (Wyoming, Montana, Idaho, Nevada, Utah, Colorado, New Mexico, Arizona, California, Oregon and Washington). All participants in the NHANES-III survey provided an informed consent to participate. Comparisons among the four regions were performed using ANOVA. Multivariate analysis was performed using multiple weighted regression analysis to perform covariate adjustments. For each blood pressure or dietary factor studied, a model was developed to compare the regional differences with adjustments for age, gender, ethnicity, body mass index (BMI) and total reported energy consumption. The data presented in the tables are unadjusted values. Results are presented as means ± SEM.
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RESULTS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONLITERATURE CITED |
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shows demographic characteristics, BMI and blood pressure in the overall sample and in each of the four regions in the United States. Mean age was lower in the south and west regions than in the northeast and midwest regions (P < 0.005). There were differences in the gender and ethnic distributions of the four regions. BMI was greater in the south than in the other regions (P < 0.005).
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, the south had the highest systolic and diastolic blood pressures (SBP and DBP, respectively) (P < 0.005 for each). When adjusted for age, ethnicity, gender, BMI and total energy intake using multivariate analysis with the western region as the reference; the south region had the highest SBP (P < 0.05) and DBP (P < 0.005); the midwest region had the lowest SBP (P < 0.005) and the east region had the lowest DBP (P < 0.005).
There were no differences in the total reported energy consumption among the four regions (Table 2
). Based on dietary self-report, the south region consumed more fatty acids than the other regions (P < 0.005). The west region consumed the largest amount of carbohydrate (P < 0.005) and protein (P < 0.005). Both the west and south regions consumed more cholesterol per day than the other regions (P < 0.005). The west region also consumed a higher amount of fiber than the other regions (P < 0.005). In the multivariate analysis, the south region consumed the most monounsaturated fatty acid, polyunsaturated fatty acid and cholesterol (P < 0.05 for all). Also, the south consumed the least amount of fiber in the multivariate analysis (P < 0.005). Reported alcohol consumption was greatest in the midwest (P < 0.005). In the multivariate analysis, the east consumed the least amount of total fatty acid (P < 0.001) and saturated fatty acid (P < 0.005).
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). After covariate adjustments, the south remained the region that consumed the most sodium per day; reported sodium consumption was 100 ± 0.2 mg greater in the south than in the west (P < 0.005). The south also consumed the least potassium, calcium, phosphorous, magnesium, copper and iron. The differences between the southern and western regions persisted in the multivariate analysis for potassium (P < 0.001), calcium (P < 0.001), phosphorous (P < 0.001), magnesium (P < 0.001), copper (P < 0.001) and iron (P < 0.001). The northeast consumed less zinc than the other regions (P < 0.05). Frequency of "adding salt to food on the table" did not differ among regions. The south consumed the least riboflavin, niacin and vitamins A, C and B-6 (P < 0.005). There were no differences in reported vitamin B-12 or thiamin consumption among the four regions.
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DISCUSSION |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Furthermore our analysis suggested that the increased cardiovascular disease in the "stroke belt" may be associated with relatively higher reported cholesterol consumption, as well as by dietary patterns that may contribute to higher levels of blood pressure. Individuals in the southern region of the United States consume the highest reported amount of sodium and the lowest reported amounts of potassium, calcium, phosphorus, magnesium, copper, iron and fiber. This analysis of NHANES III data suggests that nutritional patterns previously shown to be associated with higher blood pressure levels in across-population studies and in clinical trials are most common in the southern region of the United States (27
–29
). This could in part be associated with the higher prevalence of hypertension and the lower rate of hypertension control in this region. Although the differences in blood pressure and nutrient consumption among the four regions are relatively small, the trends are remarkable given the magnitude and diversity of the four geographic regions, the day-to-day variability of nutrient intake and the difficulty of assessing nutrient consumption. On a population level, even these small differences in blood pressure can account for a large proportion of the regional differences of cardiovascular risk profiles in the United States.
Our observations were consistent with previous reports demonstrating relatively high intakes of sodium and relatively low intakes of potassium in the southeastern United States (30
–32
). Furthermore the CARDIA study documented impressive regional differences in changes of blood pressure in a cohort of young adults at each of four sites followed periodically over 7 y. In this study although there were no regional differences at baseline, the highest incidence and prevalence of elevated blood pressure at 7 y were observed in Birmingham, Alabama, compared with Chicago, Minneapolis and Oakland, California. Estimated sodium intakes were higher and potassium and magnesium intakes were lower in Birmingham than in the other three cities (33
). The present report extended these studies by investigating variations in diet and blood pressure among different regions of the United States in a population-based survey.
Dietary factors have also been linked to stroke and stroke mortality (34
–38
). Specifically, a low potassium diet may be associated with a higher stroke mortality rate (35
–39
). Our finding of a lower potassium intake in the southern region of the United States, in addition to the higher blood pressure, may in part be associated with the higher stroke mortality rate in this region.
In a short-term controlled-feeding trial, the Dietary Approaches to Stop Hypertension (DASH) trial shows that feeding a diet high in fruits, vegetables and low-fat dairy products resulted in reductions in blood pressures in individuals with either high normal blood pressure or mild hypertension (40
). Although the DASH trial was not designed to evaluate the effects of specific nutrients on blood pressure, it is noteworthy that this diet contains 3.0 g of sodium, 4.7 g of potassium, 1240 mg of calcium, 500 mg of magnesium and 27% fatty acids. In a subsequent trial, reduction in sodium intake augments the effect of the DASH diet on blood pressure (41
). Compared with the DASH diets, the U.S. population consumes more sodium and less potassium, calcium and magnesium. This dietary pattern is particularly true for the southern region. The practical implication of these observations is that advice about nutrition and blood pressure should address the impact of the overall diet rather than focusing on any single nutrient.
We found that the southern region of the United States, which includes the "stroke belt," has dietary patterns that are associated with cardiovascular disease. We suggest that the higher intakes of fatty acids, cholesterol and sodium and the lower intakes of potassium, magnesium, calcium and fiber may be associated with the high prevalence of hypertension in the south region. Interventional strategies to lower dietary fatty acids, cholesterol and sodium and to increase dietary potassium, calcium, magnesium and fiber should be a priority to reduce these risks in the southern United States.
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FOOTNOTES |
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Manuscript received 12 August 2002. Initial review completed 26 August 2002. Revision accepted 23 September 2002.
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LITERATURE CITED |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONLITERATURE CITED |
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