Dawn K. Wilson

Effects of Potassium on Blood Pressure in Salt-Sensitive and Salt-Resistant Black Adolescents

This study examined the effects of increasing dietary potassium on ambulatory blood pressure nondipping status (<10% decrease in blood pressure from awake to asleep) and cardiovascular reactivity in salt-sensitive and salt-resistant black adolescents. A sample of 58 normotensive (blood pressure, 101/57+/-9/4 mm Hg) black adolescents (aged 13 to 16 years) participated in a 5-day low sodium diet (50 mmol/24 h) followed by a 10-day high sodium diet (150 mmol/24 h NaCl supplement) to determine salt-sensitivity status. Participants showed a significant increase in urinary sodium excretion (24+/-19 to 224+/-65 mmol/24 h) and were identified as salt-sensitive if their mean blood pressure increase was >/=5 mm Hg from the low to high sodium diet. Sixteen salt-sensitive and 42 salt-resistant subjects were then randomly assigned to either a 3-week high potassium diet (80 mmol/24 h) or usual diet control group. Urinary potassium excretion significantly increased in the treatment group (35+/-7 to 57+/-21 mmol/24 h). At baseline, a significantly greater percentage of salt-sensitive (44%) compared with salt-resistant (7%) subjects were nondippers on the basis of diastolic blood pressure classifications (P<0.04). After the dietary intervention, all of the salt-sensitive subjects in the high potassium group achieved dipper status as a result of a drop in nocturnal diastolic blood pressure (daytime, 69 versus 67 mm Hg; nighttime, 69 versus 57 mm Hg). No significant group differences in cardiovascular reactivity were observed. These results suggest that a positive relationship between dietary potassium intake and blood pressure modulation can still exist even when daytime blood pressure is unchanged by a high potassium diet.

Socioeconomic Status and Blood Pressure Reactivity in Healthy Black Adolescents

Adolescents in low-socioeconomic-status environments are more susceptible to illnesses, such as hypertension and cardiovascular diseases. This study examined the influence of both neighborhood- and family-level socioeconomic status (SES) on blood pressure (BP) reactivity in a healthy sample of 76 black adolescents. It was hypothesized that a higher level of parental education and/or income would reduce the elevated BP reactivity associated with living in poorer neighborhoods. Census-derived data were obtained using each participants address. Neighborhood level of SES was based on percentage of households below the poverty line, female-headed households, owner-occupied housing, percentage vacant housing, and average number of persons per household. Family level of SES was based on self-reported level of parental education and annual family income. Adolescents participated in a competitive video game to establish their BP reactivity scores. As predicted, adolescents who lived in poorer neighborhoods had lower diastolic BPs if their parents were more (versus less) educated (P<0.05; 7+/-8 versus 13+/-6 mm Hg). Adolescents who lived in poorer neighborhoods also had significantly lower diastolic BP reactivity (P<0.05) if their family had a higher (versus lower) annual income (7+/-7 versus 12+/-8 mm Hg). These data are the first to demonstrate the buffering effect of family SES on the negative health consequences of living in low-SES neighborhoods in healthy black adolescents.

Ambulatory blood pressure nondipping status in salt-sensitive and salt-resistant black adolescents*

This study examined the relationship between salt sensitivity and ambulatory blood pressure in 53 healthy black adolescents. Salt sensitivity was defined as an increase in mean blood pressure greater than or exceeding 5 mm Hg from a 5-day low-salt diet (50 mmol/24 h) to a 10-day high-salt diet (150 mmol/24 h NaCl supplement). Sixteen subjects were salt sensitive and 37 subjects were salt resistant (showed < 5 mm Hg increase in mean blood pressure). Subjects were classified as dippers (> or =10% decrease in blood pressure from awake to asleep) based on their 24-h ambulatory blood pressure values. Nondippers showed higher systolic, diastolic, and mean asleep blood pressures than dippers (P < .05 for all). Salt-sensitive subjects showed greater daytime diastolic and mean blood pressures than salt-resistant subjects (P < .05 for both). A significantly greater percentage of nondippers were salt sensitive, compared with salt resistant for diastolic blood pressure (P < .001) and mean blood pressure (P < .05). For both of these blood pressure measures, 50% of the salt-sensitive subjects had a nondipping status, compared with only 5.4% of the salt-resistant subjects for diastolic blood pressure, and 18.9% of the salt-resistant subjects for mean blood pressure. These results are the first to indicate that salt sensitivity is associated with nondipper blood pressure status in a black normotensive adolescent population.

The Role of Gender and Family Support on Dietary Compliance in an African American Adolescent Hypertension Prevention Study

Social support experiences vary markedly across gender groups, and little is known about the role of social support in promoting healthy dietary compliance in African American adolescents who are at increased risk for developing hypertension. This study examined the relation between gender, dietary social support, and compliance to a low sodium diet. Casual blood pressures were also examined in relation to dietary compliance and gender. One hundred eighty-four healthy African American adolescents (83 boys, 101 girls) participated in an intensive 5-day low sodium diet (50 mEq/24 hr) as part of a hypertension prevention program. Emotional dietary social support from family members and friends was measured at baseline. Compliance was defined as urinary sodium excretion of≤ 50 mEq/24 hr at postsodium restriction. The results indicated a significant Gender × Compliance effect for positive family support (p > .05). Girls who were compliant reported higher levels of dietary support from family members (19.2 ± 7.8) than boys who were compliant (16.9 ± 7.0). In contrast, boys who were compliant reported lower levels of dietary support from family members (16.9 ± 7.0) than boys who were not compliant (20.2 ± 7.5). Systolic blood pressure showed a trend toward decreasing in compliant participants (104.4 ± 8.4 vs. 101.7 ± 8.0, mm Hg, p > .06), but the effect diminished when Quetelet Index (kg/m2) was controlled for in the analyses (p > .12). These results suggest that higher levels of emotional dietary support from family members are associated with better adherence to short-term sodium restriction for African American girls as compared to boys. Further research is needed to determine the long-term impact of social support on sodium restriction in adolescent populations.

The influence of gender and emotional versus instrumental support on cardiovascular reactivity in African-American adolescents

Research suggests that females seek out, prefer, and are more receptive to emotional support (encouragement), and that males seek out, prefer, and are more receptive to instrumental support (problem-solving). Thus, we hypothesized that boys would show lower blood pressure (BP) reactivity in response to instrumental than emotional or no support, and that girls would show lower BP reactivity in response to emotional than instrumental or no support. Forty-eight healthy African-American adolescents (50% males) participated in a role play conflict task and were randomized to receive either emotional, instrumental, or no support (presence only) from a confederate. Boys showed lower systolic blood pressure (SBP) reactivity in the instrumental than in the emotional or no support conditions and lower recovery SBP as compared to boys in the emotional or no support conditions. A similar pattern of results was demonstrated for diastolic blood pressure (DBP) reactivity. Girls, however, did not demonstrate lower BP reactivity in response to emotional as compared to instrumental support. These findings suggest that instrumental and emotional support differentially influence cardiovascular (CV) reactivity in African-American boys versus girls.

Variability in Salt Sensitivity Classifications in Black Male Versus Female Adolescents

Salt sensitivity (changes in blood pressure in response to alterations in salt intake) may be a risk factor for hypertension. In the present study, we examined the prevalence of salt sensitivity based on two different classifications in healthy black male and female adolescents (aged 13 to 16 years). A total of 135 black adolescents participated in a 50 mmol/24 h low sodium diet for 5 days and a 150 mmol/24 h NaCl supplement for 10 days. Dietary compliance was defined as sodium excretion less than or equal to 50 mmol/24 h for the low sodium diet and greater than or equal to 165 mmol/24h for the high NaCl supplement. Salt sensitivity was defined by two classifications: (1) as a decrease in mean blood pressure greater than or equal to 5 mm Hg from baseline to the low sodium diet, and (2) as an increase in mean blood pressure greater than or equal to 5 mm Hg from the low sodium diet to the high NaCl supplement. With classification 1, 14% of boys were identified as salt sensitive compared with 22% of girls. With classification 2, however, 31% of boys were identified as salt sensitive compared with 18% of girls. Analyses based on changes in systolic pressure demonstrated similar findings across sex, although overall classifications based on systolic pressure yielded a greater percentage of salt-sensitive subjects. These sex differences in classification patterns were not due to differences in other important variables, such as changes in sodium excretion, potassium excretion, or Quetelet index. These results suggest that the prevalence of salt sensitivity differs by sex depending on the type of protocol used for the classification of salt sensitivity in a black pediatric population.

Introduction to the special issue: Innovative approaches to health behavior change

The promotion of healthy life-styles is especially important for reducing mortality from cardiovascular diseases, obesity, diabetes mellitus, cancer, and human immunodeficiency virus (HIV) (1-3). Risk factors such as poor diet, lack of physical activity, smoking, substance abuse, and sexual risk behaviors have all been linked to disease progression. For example, intake of specific nutrients such as dietary fat, cholesterol, and sodium have been linked to elevated blood cholesterol, obesity, and high blood pressure (4). Behaviors such as lack of physical activity and cigarette consumption have also been linked to the development of cardiovascular disease and cancer (5,6). Sexually transmitted diseases and HIV also pose a significant threat to individuals who engage in unprotected sex (7). Over the past several decades, the field of behavioral medicine has demonstrated that modifying behavioral risk factors is an effective method for preventing disease (8-10). Theoretical-based innovative approaches to behavior change, however, are still not firmly established within the field. This special issue highlights a series of articles that focus on theoretically-based innovative approaches to health behavior change. The papers were all selected as representing exceptional work presented at the Eighteenth Annual Society of Behavioral Medicine Conference held in San Francisco in 1997. The articles included in this series are unique in that they highlight approaches for promoting health behavior change that are creative and feasible in public health settings. Many of the studies also test competing theoretical approaches to modifying behavior. In short, each study gives a well-designed theoretically-based approach that clearly advances on past research. The lead article, Kaplans Presidential Address, reflects an innovative perspective on decision-making which advocates a more active role on the patients behalf. In particular, Kaplan highlights the fact that many medical procedures that may effect biological processes may not address important issues such as life expectancy or life quality. In his address, he advocates a model known as the outcomes model which emphasizes quality of life and life duration instead of clinical measures of disease process. This approach has important implications for the organization, financing, and delivery of health care. In the next three articles by Eitel and Friend, Hendy, and Miller et al., a set of unique methodologies are employed to test the

Cardiovascular reactivity in Black and White siblings versus matched controls.

Elevated cardiovascular (CV) reactivity may be a marker or mechanism for the early development of essential hypertension (EH) and may contribute to the greater prevalence of EH observed in Black adults. Previous research has demonstrated that Black children show greater CV reactivity than White children to psychological stressors, however, the role of heritability in understanding these racial differences is still unknown. Evidence which supports a genetic influence on CV reactivity comes from animal studies, research on family history of EH, and from twin and sibling studies. The present study expands on previous findings by examining racial differences in CV reactivity in 15 pairs of Black siblings, 15 pairs of age-and sex-matched unrelated Black control subjects, 17 pairs of White siblings, and 17 pairs of age-and sex-matched unrelated White control subjects. Systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) measurements were obtained at rest and during a stress task (competitive video game). Black siblings demonstrated a significantly higher intraclass correlation for DBP reactivity than Black controls or White siblings (r=0.73, versus 0.16, 0.14, respectively). Additionally, Black siblings demonstrated a steeper rise and then a plateau in DBP and HR reactivity to the video game task, while White siblings showed a more gradual increase in these measures over the course of playing three video games. The results for DBP and HR reactivity, however, were not consistent among either of the matched control groups. These results expand on previous research by suggesting a stronger genetic influence of CV reactivity in Black than in White children.