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(Hypertension. 1996;28:228-237.)
© 1996 American Heart Association, Inc.
Articles |
Trial of Stress Reduction for Hypertension in Older African Americans
II. Sex and Risk Subgroup Analysis
the Department of Psychology (C.N.A., B.M.C., M.R., K.K., K.G.W.) and Center for Health and Aging Studies, Department of Physiological and Biological Sciences (C.N.A., R.H.S., J.S., K.K., K.G.W.), Maharishi University of Management, Fairfield, Iowa; Hypertension and Stress Management Research Clinic, West Oakland (Calif) Health Center (F.S., W.S., S.S.); Haight-Ashbury Free Medical Clinic, San Francisco, Calif (F.S.); and Medical University of South Carolina, Charleston (B.E.). Preliminary portions of this study were presented at the Society of Behavioral Medicine, San Diego, Calif, March 22-25, 1995, and at the Centennial Conference of the National Medical Association, Atlanta, Ga, July 29 to August 3, 1995.
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Abstract |
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Our objective was to test the short-term efficacy and feasibility of two stress-reduction approaches for the treatment of hypertension in older African Americans, focusing on subgroup analysis by sex and by high and low risk on six measures of hypertension risk: psychosocial stress, obesity, alcohol use, physical inactivity, dietary sodium-potassium ratio, and a composite measure. The study involved a follow-up subgroup analysis of a 3-month randomized, controlled, single-blind trial conducted in a primary care, inner-city health center. Subjects were 127 African American men and women, aged 55 to 85 years, with diastolic pressure of 90 to 104 mm Hg and systolic pressure less than or equal to 179 mm Hg. Of these, 16 did not complete follow-up blood pressure measurements. Mental and physical stress-reduction approaches—the Transcendental Meditation technique and progressive muscle relaxation, respectively—were compared with a lifestyle modification education control and with each other. Both systolic and diastolic pressures changed from baseline to follow-up for both sexes and for high and low risk level (defined by median split) on the six measures of hypertension risk. Compared with education control subjects, women practicing the Transcendental Meditation technique showed adjusted declines in systolic (10.4 mm Hg, P<.01) and diastolic (5.9 mm Hg, P<.01) pressures. Men in this treatment group also declined in both systolic (12.7 mm Hg, P<.01) and diastolic (8.1 mm Hg, P<.001) pressures compared with control subjects. Women practicing muscle relaxation did not show a significant decrease compared with control subjects, and men declined significantly in diastolic pressure only (6.2 mm Hg, P<.01). For the measure of psychosocial stress, both the high and low risk subgroups using the Transcendental Meditation technique declined in systolic (high risk, P=.0003; low, P=.06) and diastolic (high risk, P=.001; low, P=.008) pressures compared with control subjects, whereas for muscle relaxation, blood pressure dropped significantly only in the high risk subgroup and only for systolic pressure (P=.03) compared with control subjects. For each of the other five risk measures, Transcendental Meditation subjects in both the high and low risk groups declined significantly in systolic and diastolic pressures compared with control subjects. Effects of stress reduction on blood pressure were found to generalize to both sexes and diverse risk factor subgroups and were significantly greater in the Transcendental Meditation treatment group. These effects (along with high compliance) even in individuals with multiple risk factors for hypertension clearly warrant longer-term investigation in this and other populations.
Key Words: stress • risk factors • meditation • relaxation • blacks • blood pressure
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Introduction |
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The age-adjusted rate of hypertension in African American adults is more than 50% higher than for white Americans,1 and African Americans die from hypertensive diseases at substantially higher rates than do whites.2 3 These disparities in hypertension and related mortality may be partly due to the higher prevalence and severity of several hypertension risk factors in African Americans, including psychosocial stress, obesity, alcohol use, physical inactivity, and sodium sensitivity.1 When these risk factors occur in combination, they appear to produce a multiplicative effect, substantially increasing the likelihood of hypertension and subsequent cardiovascular disease.4 African Americans are 50% more likely than whites to display multiple risk factors for cardiovascular disease.1
There are also important sex differences in hypertension and related risk factors in African Americans. Elderly black women show the highest prevalence of hypertension (>75%) of any race/age subgroup,5 and their age-adjusted total mortality rate for heart disease is two thirds higher than for white women. Moreover, black women are twice as likely as both white women and black men to be obese.6 With respect to black men, the age-adjusted total mortality rate from heart disease is 33% higher than in white men. Moreover, compared with black women, there is evidence that black men have a higher drinking rate,7 lower compliance with antihypertensive medication,8 a lower leisure-time physical activity rate,1 and higher psychosocial stress on some indicators, as suggested, for example, by higher rates of suppressed hostility and suicide.9 10
Not only are African Americans exposed to more extreme socioenvironmental stressors than whites,11 but they also may show greater cardiovascular and sympathetic reactivity to such stressors.12 Psychosocial stress also may contribute indirectly to high BP by increasing the intensity and clustering of other maladaptive behavioral responses associated with an increased risk of hypertension (eg, obesity and alcohol abuse). Stress related to mounting socioeconomic and health problems later in life may particularly place elderly African Americans at multiple jeopardy for hypertensive disease.7 Moreover, there may be significant sex differences in the contribution of stress to hypertension. A recent study13 found that high levels of anxiety/tension predicted the subsequent development of hypertension in older men but not in older women in the general population; it was recommended that future studies assess this sex difference specifically for African Americans.
Given the contribution of stress to the etiology of hypertension in older African Americans, the application of behavioral methods for stress reduction would seem particularly relevant to this population. Yet with the exception of our own recent study,14 no trials have been reported on stress management in the treatment of hypertension in elderly African Americans.15 In our original randomized controlled trial in hypertensive older African Americans, we found that compared with a lifestyle education control (EC) group, the Transcendental Meditation (TM) technique, a mental technique for stress reduction, reduced systolic and diastolic BPs approximately twice as much as a physical relaxation approach, progressive muscle relaxation (PMR), after 3 months of follow-up.14 These results were consistent with recent statistical meta-analyses in primarily white populations indicating that the TM technique reduced several risk behaviors—including acute and chronic physiological arousal,16 alcohol and cigarette use,17 anxiety,18 and poor self-esteem19 —significantly more than other forms of relaxation.
In light of the significant contribution of sex differences and the increased frequency of hypertension risk behaviors in hypertensive African Americans, we reanalyzed data from our original study to address two clinically important questions: Will application of these stress-reduction techniques in older African Americans produce similar BP reductions for (1) both sexes and (2) individuals at high as well as low levels on several hypertension risk factors, including psychosocial stress, obesity, alcohol use, physical inactivity, sodium-potassium ratio, and a composite measure of risk?
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Methods |
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More detailed methods are described in the original study.14
Subjects
Criteria for subject selection included self-identification as African American, age 55 years and older, and hypertension initially defined as 90 to 109 mm Hg DBP and less than or equal to 189 mm Hg SBP based on three measures taken at the screening visit. BP and quality of life measures were assessed during four subsequent baseline visits over a 1- to 2-month period. Subjects were subsequently excluded from the study if their BP exceeded 104 mm Hg DBP or 179 mm Hg SBP on two successive baseline visits. Volunteers taking antihypertensive medications were eligible for the trial, as were individuals not taking BP medications, if they met the entry criteria noted above and if they did not change their medication regimen during either the baseline or treatment phase of the study. The trial was conducted at the West Oakland Health Center, a primary care community health center in Oakland, Calif. This study was approved by the institution's Committee for Protection of Human Subjects. All subjects gave informed consent to participate.
Treatments
After completing the baseline period, subjects were randomly assigned to one of three treatment conditions: (1) The TM program, the principle technology of consciousness of the Maharishi's Vedic Approach to Health, which has been recently described by Nader20 as a comprehensive, prevention-oriented system of natural health care brought to light by Maharishi Mahesh Yogi from the ancient Veda and Vedic literature21 22 ; (2) PMR, a widely studied physical approach, adapted by Bernstein and Borkovec23 from Jacobson's original technique for systematically relaxing the major muscle groups of the body24 ; and (3) a lifestyle-modification education control (EC) based on guidelines for nondrug treatment of hypertension recommended by the Joint National Committee.25 The two active stress-reduction procedures were matched for expectancy of benefits, teaching format, instructional time, and home practice (20 minutes twice a day), and neither required change in personal beliefs or lifestyle. Initial instruction occurred over 1 week, with 1.5-hour monthly follow-up meetings. To partially control for attention and expectancy, EC subjects also met with treatment providers for 1-hour follow-up sessions monthly and were given the expectation that their BP could be managed by adopting the lifestyle changes that were recommended.
Measures
BP follow-up took place monthly for 3 months. The final posttest assessment was based on the average of two BP measurements taken 1 week apart during the 11th and 12th weeks. BPs were measured with an automated BP monitor (model 300S, Vitastat Medical Services) with digital readout calibrated against a mercury sphygmomanometer at regular intervals. BP measurements (by testers blind to the subject's treatment status) were taken after subjects sat for 5 minutes without practicing any relaxation techniques. During each visit, three assessments were taken at 1-minute intervals using the first and fifth Korotkoff sounds, with the final reading based on the average of the last two measurements.
Six factors related to hypertension risk were measured at pretest. Subjects were not stratified on these variables before randomization. Instead, they were divided into high and low risk levels on each of these parameters for subsequent subgroup analysis. This method not only controlled for potential differences between groups on each risk factor but allowed assessment of the generalizability of treatment effects across risk level for the various factors (see "Data Analysis"). The six risk factor measures were as follows: (1) Obesity: Subjects were weighed without shoes or outdoor garments on a balance scale that also measured height (Healthometer, 402KL). BMI was calculated from weight and height (kilograms per meter squared). (2) Alcohol consumption: The number of drinks per week (with one drink defined as 12 oz of beer, 5 oz of wine, or 1.5 oz of liquor) was assessed by a short questionnaire adapted from the Multiple Risk Factor Intervention Trial (MRFIT).26 (3) Physical exertion level: The number of hours per day of moderate or vigorous physical activity was assessed by a questionnaire adapted from MRFIT.26 (4) Dietary sodium-potassium: Intake of sodium and potassium was estimated from the Trials of Hypertension Prevention Health Habits Questionnaire and was calculated with a normative database of standard portion sizes and nutrient contents.27 Because some researchers consider low potassium intake (in addition to high sodium intake) to be a contributor to hypertension risk28 and to control for response differences in the ability of subjects to recall all foods eaten, the ratio of sodium intake to potassium intake was used as the outcome measure. (5) Psychosocial stress: A battery of psychosocial measures of quality of life was administered verbally and individually to each participant over three pretest sessions and again at posttest. The battery included the personal efficacy subscale from the National Survey of Black Americans29 ; trait anxiety and trait anger subscales from the State-Trait Personality Inventory30 ; the Rosenberg Self-Esteem Scale; well-being as measured by the Affect Balance Scale31 ; global score on the Nottingham Health Profile, which contains four subscales measuring physical health and two measuring psychosocial health32 ; total score on the short-form Duke University Multidimensional Health Profile, which contains five subscales assessing general health, symptoms, and physical, social, and emotional functioning; and total score on the health problems and impact subscale of the Index of Illness. Because of the large number of quality of life measures, we performed a principle components analysis to identify a smaller number of underlying quality of life factors, thus reducing the probability of a type 1 error.33 The first factor, which accounted for the largest proportion of variance (28%), was taken as an indicator of psychosocial stress. It was composed of high scores on trait anger and anxiety and low scores on self-esteem, well-being, and personal efficacy (with factor loadings 
0.50). Both anger and anxiety have been implicated in high BP,34 35 and more recently, psychosocial "cushioning" factors such as self-esteem have been seen to protect against hypertension.36 37 (6) Multiple risk factors: The prevalence of multiple risk factors was determined by score on a weighted composite index for the above five risk factors as determined by multiple regression (see "Data Analysis").
Data Analysis
Baseline characteristics of the three groups were compared by MANOVA and ANOVA. The baseline characteristics included age, sex, BMI, BP, medication status, and psychological and behavioral/lifestyle characteristics. Significance was set at a value of P<.05 for these and all other statistical comparisons.
Treatment outcomes were assessed by ANCOVA, with treatment status as the independent variable, changes in SBP and DBP as the dependent variables, and baseline SBP and DBP and other baseline characteristics that significantly differed between the groups as covariates. Change in BP was defined as 3-month posttreatment BP minus baseline BP. Additionally, two types of intent-to-treat analyses were performed for determination of whether lost data due to dropouts altered the results. First, missing BP change scores were treated as missing at random, and the BMDP 5V routine33 was applied for estimation of group means from all available data. Second, more conservatively, the maximum increase in BP observed in any subject was applied as the missing value for all subjects.
For assessment of treatment outcomes in relation to sex, separate ANCOVAs were performed within sex subgroups using the same independent variable, dependent variables, and covariates as in the analysis of outcomes for the entire sample. Also, repeated measures ANCOVAs based on all three posttest visits examined monthly BP change within the sex subgroups.
Similar to the within-subgroups analyses for sex, treatment effects were separately assessed by ANCOVA comparing each high and low risk subgroup, formed by median split on each risk factor. In addition to examination of the five individual risk factors taken separately, these factors were used in combination to create an index of overall hypertension risk. This was accomplished by performing regression analysis on the data for the control group alone to predict BP change over 3 months. Separate regression models were constructed for SBP and DBP as the dependent variables, with the pretest levels of the five risk factors as the explanatory or independent variables. The two regression models accounted for 29.8% of the SBP change score and 25.9% of the variance in DBP change, respectively. The coefficients from these models yielded two regression equations from which were constructed two composite indexes for relative risk of increase in SBP and DBP. As with the individual risk factors, the sample was divided by median split on the two composite indexes. The same ANCOVAs as for the separate risk factors were performed on the overall high and low risk subgroups, based on the composite SBP risk index for SBP change and the composite DBP index for DBP change.
Planned contrasts allowed pairwise comparisons of the three treatment groups on BP outcomes. These contrasts were one-tailed because of directionality of predictions. Given our initial findings on the effects of stress reduction on BP reduction in African Americans14 and previous research suggesting the generalizability of effects (especially of the TM technique) across sex and in various high-risk populations,38 it was hypothesized that for each sex and for each risk level (ie, high and low) on the various risk factors, both active interventions would be more effective than the EC intervention and that the TM group would show greater reductions in BP than the PMR group. Two-tailed tests were used for statistical comparisons that did not evaluate effects of treatment (eg, on outcome differences by sex or risk level within each treatment group).
We performed power analyses to assess the statistical power to conduct the above subgroup analyses. In the original study,14 with 37 subjects per treatment group, effect size differences between treatments were as follows: TM-EC=0.88 for SBP and 0.94 for DBP; PMR-EC=0.38 for SBP and 0.49 for DBP; TM-PMR=0.49 for SBP and 0.46 for DBP. Assuming that effect size differences between treatments were the same for both women and men; that cell sizes were 21.3 and 15.7 subjects, respectively; and that ANCOVA with one-tailed planned comparisons at the 5% significance level were used, power for treatment comparisons in women was as follows: for TM versus EC, 88% to 92%; TM versus PMR, 43% to 47%; and PMR versus EC, 34% to 47%. In men it would be as follows: TM versus EC, 77% to 83%; TM versus PMR, 35% to 38%; and PMR versus EC, 28% to 38%. Power for comparisons at different risk levels was similar to that for these sex comparisons. Assuming identical effect size differences between treatments for both the high and low risk subgroups and all cell sizes of 18.5 due to median split on each risk factor, the power for treatment comparisons for both risk levels would be as follows: for TM versus EC, 83% to 88%; TM versus PMR, 39% to 43%; and PMR versus EC, 31% to 42%. Thus, given the large effect size differences between TM and EC, there was ample power for detection of differences between these treatment conditions in the various subgroup analyses. Given the smaller effect size differences for the other treatment comparisons, the power for detection of differences was correspondingly reduced.
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Results |
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Baseline Characteristics
As previously described,14 127 subjects were randomized to treatment groups. There was a 12.6% attrition rate over 3 months of treatment, resulting in a final sample of 111 subjects. Of the 16 subjects lost to follow-up, 11 dropped out because of change in hypertensive medication (2 in the TM group; 3, PMR; 6, EC); the 5 others dropped out primarily because of change in residence (2 in the TM group; 2, PMR; 1, EC). There was no sex difference in attrition rates. Pooling across sex, MANOVA showed no overall significance between treatment groups on the 19 baseline physiological and quality of life variables. Univariate ANOVA indicated that only age significantly differed between groups (TM=63.7 years, PMR=69.2 years, EC=67.4 years; P<.01). However, in this sample, age was not found to be significantly correlated with SBP or DBP either at baseline or with change in BP over time.
Table 1
presents baseline BP and demographic characteristics separately for women and men for each treatment group. In the total sample, 58% were women (n=74) and 42% (n=53) were men. Women (mean age, 67.9 years) were significantly older (P<.05) than men (mean age, 64.8 years). Also, BMI was significantly higher for women than for men (P=.015), and as assessed by 
2 analysis, significantly more women (45%) were obese (BMI >30.0 kg/m2) than men (23%). Approximately half of the total sample was taking hypertensive medications (55.4% of the women, and 41.5% of the men). Baseline SBP for women (150.1 mm Hg) was significantly higher (P<.05) than for men (143.5 mm Hg); DBP did not differ significantly between sexes.
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Participants' monthly reports indicated high compliance rates for the active treatments: 97.1% of the TM group and 81.1% of the PMR group practiced their programs twice daily or almost twice daily. By test of proportion, compliance rates did not significantly differ between these two groups. Both groups rated their instructors as "excellent" (3.9 on a 4-point scale).39 The groups also did not differ on a measure of expectancy of positive outcomes from treatment. All three groups expected to change substantially, as indicated by high scores on a 4-point scale (3.2 for the TM group; 3.1 for PMR; 3.1 for EC). Also, there were no sex differences for compliance rate or expectancy.
BP Changes in Women and Men
Pooling across treatment groups, ANCOVA indicated that the change in SBP in women (-6.7 mm Hg) was significantly greater (P<.05, two-tailed) than in men (-3.3 mm Hg) over the 3-month period; however, there was no significant sex difference in DBP change. For each treatment group, Table 2 presents, separately for women and men, the raw SBP and DBP change scores and change scores adjusted for age and baseline SBP and DBP covariates. Compared with EC women, TM women showed an adjusted decrease of 10.4 mm Hg in SBP (P<.01) and 5.9 mm Hg in DBP (P<.01). Compared with EC women, PMR women showed a nonsignificant decrease of 4.8 mm Hg in SBP and 1.9 mm Hg in DBP. Compared with PMR women, TM women showed nonsignificant decreases of 5.6 mm Hg in SBP and 4.0 mm Hg in DBP. Compared with EC men, TM men showed significant adjusted decreases of 12.7 mm Hg in SBP (P<.01) and 8.1 mm Hg in DBP (P<.001). Compared with EC men, PMR men showed a nonsignificant reduction of 6.1 mm Hg in SBP and a significant reduction of 6.2 mm Hg in DBP (P<.01). Compared with PMR men, TM men showed a significant reduction of 6.6 mm Hg in SBP (P<.05) and a nonsignificant decrease of 1.9 mm Hg in DBP. Probability values for the two intent-to-treat analyses were consistent with those from the primary BP analyses. Also, continuing subjects and dropouts did not differ significantly in baseline BP, demographics, and quality of life variables.
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Fig 1 shows SBP (top) and DBP (bottom) changes adjusted for baseline levels and age for the 60 women with complete data for each of the three monthly follow-up visits. Fig 2 presents the same BP changes for the 44 men with complete data. Compared with EC women, TM women showed a significant decrease in SBP (P<.01) and DBP (P<.009), whereas PMR women did not. Compared with PMR women, TM women showed a decline in DBP (P<.07, trend) but not SBP. Compared with EC men, TM men showed significant decreases in SBP (P<.0004) and DBP (P<.00005), and PMR men in DBP (P<.02) but not SBP. Compared with PMR men, TM men showed a significant decline in SBP (P<.01) and DBP (P<.08, trend).
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Moderating Role of Risk Factors for Hypertension
In Table 3, change scores in SBP and DBP for the three treatment groups are separately presented (covarying for baseline BP and age) by low and high level on the various hypertension risk factors.
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Psychosocial Stress
The composite psychosocial stress score (Z-score sum of scores) for the high risk subgroup was greater than or equal to -0.13 SD units. Fig 3 shows adjusted SBP (top) and DBP (bottom) change scores for the high and low risk subgroups in each treatment grouping. For both high and low risk subgroups, the TM group had significantly lower SBP (ie, adjusted mean change; high, P=.0003; low, P=.06, trend) and lower DBP (high, P=.001; low, P=.008) compared with the EC group. For the PMR group, only the high risk subgroup had significantly lower SBP (P=.03) compared with the EC group. Compared with PMR subjects, TM subjects had lower SBP (high, P=.06, trend; low, P=.05) and lower DBP (high, P=.05; low, P=.06, trend).
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Obesity
As determined by median split, BMI for the high risk subgroup was greater than or equal to 28.8 kg/m2 for women and greater than or equal to 26.1 kg/m2 for men. For both the high and low risk subgroups, TM subjects had significantly lower SBP (high, P=.002; low, P=.007) and lower DBP (high, P=.006; low, P=.0004) compared with EC subjects. For the PMR group, the low risk subgroup had significantly lower SBP (P=.04) and the high risk subgroup had lower DBP (high, P=.03; low, P=.08, trend) compared with the EC group. Compared with PMR subjects, TM subjects had significantly lower SBP in the high risk subgroup (P=.01) and lower DBP in the low risk subgroup (P=.02). When obese versus nonobese subgroups were formed according to standard BMI criteria for women and men (rather than using the BMI medians), similar results were obtained.
Alcohol Use
Because about half the members of each group reported total abstinence from alcohol, the high risk alcohol-use subgroup was composed of all reported drinkers. For the high and low risk subgroups, TM subjects had significantly lower SBP (high, P=.00005; low, P=.02) and lower DBP (high, P=.00005; low, P=.02) compared with EC subjects. PMR subjects had significantly lower SBP (P=.0004) and DBP (P=.0002) in only the high risk subgroup compared with EC subjects. Compared with PMR subjects, TM subjects had significantly lower SBP (P=.01) and lower DBP (P=.02) in the low risk but not the high risk subgroup.
Physical Inactivity
The number of hours per day spent in either moderate or vigorous physical activity by the high risk subgroup (ie, less physically active) was 2 hours or fewer. For both the high and low physical inactivity subgroups, TM subjects had lower SBP (high, P=.07, trend; low, P=.0001) and lower DBP (high, P=.005; low, P=.001) compared with EC subjects. Only the low physical inactivity subgroup of the PMR group had significantly lower SBP (P=.04) and lower DBP (P=.04) compared with the EC group. Compared with PMR subjects, the low physical inactivity TM subgroup had lower SBP (P=.03) and DBP (high, P=.09, trend; low, P=.09, trend).
Dietary Sodium-Potassium
The ratio of dietary sodium to potassium intake was greater than or equal to 1.11 for the high risk subgroup. For both high and low risk subgroups, TM subjects had significantly lower SBP (high, P=.06, trend; low, P=.0009) and lower DBP (high, P=.001; low, P=.003) compared with EC subjects. Compared with EC subjects, PMR subjects had significantly lower SBP (P=.02) and DBP (P=.01), but for the low risk subgroup only. Compared with PMR subjects, TM subjects showed a significant decrease in both SBP (P=.04) and DBP (P=.003) in the high risk but not the low risk subgroup.
Multiple Risk Factor Index
Subjects at high risk for a rise in BP were those with a predicted increase, based on all five risk factors, of greater than or equal to 0.94 mm Hg for SBP and greater than or equal to 0.37 mm Hg for DBP. For both high and low combined risk levels, TM subjects showed significant decreases in both SBP (high, P=.00005; low, P=.06, trend) and DBP (high, P=.0001; low, P=.004) compared with EC subjects. Compared with EC subjects, PMR subjects also showed significant decreases in SBP (P=.001) and DBP (P=.0004) but only for the high risk subgroup. Compared with PMR subjects, TM subjects showed significantly lower SBP (P=.04) and DBP (P=.002) for the low risk but not the high risk subgroup alone (see Table 3
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Although smoking is not a major risk factor for hypertension, it is for congestive heart disease. Thus, for the purposes of exploratory analysis, a high risk (for congestive heart disease) smoking subgroup was composed of all self-reported smokers. For both high and low risk smoking subgroups, TM subjects showed significant decreases compared with EC subjects in both SBP (high, 15.4 mm Hg, P=.013; low, 10.0 mm Hg, P=.003) and DBP (high, 9.7 mm Hg, P=.02; low, 5.2 mm Hg, P=.002). Compared with EC subjects, PMR subjects showed a significant decrease only for the low risk subgroup in DBP (2.4 mm Hg, P=.05). Compared with PMR subjects, TM subjects showed decreases in SBP for high risk (P=.09, trend) and low risk (P=.05) smoking subgroups and in DBP for the low risk subgroup (P=.07, trend).
To further assess the generalizability of treatment effects across high and low risk levels, we determined within each treatment group whether the effects on BP were similar (or different) for high and low risk subjects for each risk behavior. Within the TM group, the reduction in SBP or DBP did not differ significantly for subjects at either high risk or low risk on five of the six hypertension risk factor outcomes. The only exception was on the overweight factor: TM subjects who were of normal weight reduced DBP significantly more (P=.01) than those who were overweight; however, there was no difference in SBP. Also, for PMR subjects, there was no difference between subjects at high and low risk on the various risk factors. In contrast, for the EC group, subjects at high levels on four of the six risk variables showed a significant increase in SBP and DBP compared with subjects at low levels, including psychosocial stress (SBP, P=.01; DBP, P=.07, trend), physical inactivity (SBP, P=.004; DBP, P=.004), alcohol (SBP, P=.0002; DBP, P=.0003), and the overall index (SBP, P=.0004; DBP, P=.0003). For the obesity and sodium-potassium risk factors, SBP/DBP reduction did not differ by risk level for the EC group.
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Discussion |
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Our original study was the first randomized controlled trial directly comparing the effects of mental and physical stress-reduction methods on hypertension in African Americans.14 To our knowledge, this follow-up study is the first to systematically investigate the applicability of stress-reduction techniques to different hypertension risk factor subgroups among African Americans. Moreover, few, if any, such risk factor subgroup studies have been conducted with behavioral approaches, even in the general elderly population.
The results of our subgroup analyses indicate the feasibility and short-term efficacy of the use of stress-reduction approaches in the treatment of hypertension in older African Americans of both sexes who are at high as well as low risk for six hypertension-related measures of risk: obesity, alcohol use, psychosocial stress, dietary sodium-to-potassium ratio, physical inactivity, and presence of multiple risks. After 3 months of follow-up, the TM technique significantly decreased SBP and DBP in both men and women compared with the EC group, whereas PMR significantly decreased DBP in both women and men but did not reduce SBP in either sex. For both women and men, the TM stress-reduction approach appeared to have an effect size approximately twice that of PMR. Furthermore, pooling across sexes, for both high and low risk factor subgroups, the TM technique decreased both SBP and DBP significantly more than the EC group for all six hypertension risk factors. For both high and low risk subgroups, PMR decreased SBP and DBP significantly more than the EC group for approximately half of the risk subgroup outcomes. For both high and low risk levels, the TM technique again reduced SBP and DBP approximately twice as much as PMR across the various risk factors.
These findings are likely to be internally valid because a randomized, single-blind design was used and multiple BP measures were taken during four baseline visits to minimize regression to the mean or white coat effects. Moreover, the use of two behavioral approaches in the same experimental setting allowed control for nonspecific intervention effects, with both active groups given similar expectancy of benefits, attention from trainers, and time allotted for daily practice. External validity was enhanced by conducting the trial in a major primary care center in a large inner-city African American community, thus increasing the likelihood of the generalizability of results to other such community settings. In addition, the baseline sex differences found in this study, including higher BMI and SBP in women and lower use of antihypertensive medication in men, are consistent with those seen in the larger older African American population.40 41 However, it should be noted that within each sex taken separately, ie, for men as well as women, the TM technique reduced BP more than PMR or EC. This was not simply because of differences in adherence to treatment, because compliance was high in both active treatment groups. Also, all subjects were included in the analysis irrespective of compliance levels.
The potential effects of methodological constraints in this study deserve examination. First, despite randomization, age significantly differed across groups at pretest. On the other hand, statistically covarying for age did not significantly alter treatment outcomes. Also, with 19 demographic and quality of life variables, one variable would be expected to be significant because of chance alone. Second, with the exception of obesity, all other risk factors were assessed by self-report, which may be less reliable than more objective methods of assessment. Although the "absolute" levels on the self-report measures may not be fully accurate, we used median splits to divide subjects into subgroups that were at least "relatively" higher or lower on the risk factor in question. The efficacy of this approach was supported by the finding that baseline differences on these risk measures tended to predict subsequent change in BP, as assessed by the multiple regression model. Third, because of the division into subgroups for analysis, sample size and hence statistical power was reduced in some cases. Power to detect differences between the TM and EC groups remained high (77% to 92%) but was lower for detecting differences between the stress-reduction approaches (35% to 47%) and between the PMR and EC groups (28% to 47%). However, significant differences in BP declines between the stress-reduction approaches and between PMR and EC were nevertheless found. Repeated measures ANCOVA of the subgroup data over the 3-month treatment period tended to yield more significant results because this statistical analysis enhances statistical power by reducing within-subject variance.
A final methodological concern is the relatively short (3 months) duration of the study. A critical question is whether these treatments will remain effective in reducing BP in both sexes and in the various risk factor subgroups over the long term. Studies of lifestyle modification approaches, particularly strict dietary regimens, have found it difficult to sustain generally more modest BP reductions over the long term.42 Intensive exercise programs, on the other hand, produce BP reductions similar to those found here in the TM group, but such programs appear to have lower compliance rates.43 44 We are currently conducting randomized controlled trials on the longer-term effects of these stress-reduction techniques on both hypertension and hypertensive heart disease in African Americans.
The results of many of the subgroup analyses are not only statistically significant, they are also potentially clinically significant. For example, the BP reductions through TM in the high psychosocial stress subgroup (11.3/5.3 mm Hg) and in the low psychosocial stress subgroup (11.4/6.4 mm Hg) are similar to those reported in antihypertensive drug trials.45 Comparable BP reductions in drug trials over the long term are associated with 35% to 40% less stroke and 20% to 45% less congestive heart disease morbidity.46 This is consistent with the results of a recent follow-up study47 of our randomized controlled trial with white elderly subjects39 showing lower cardiovascular and all-cause mortality rates and longer survival time over 8-year and 15-year periods in the TM group compared with two other mental techniques and usual care.
The results in this study also compare well with those reported for lifestyle-modification approaches. For example, meta-analyses show BP reductions of approximately 6/3 mm Hg in controlled trials of weight loss,48 dietary sodium reduction,49 and aerobic exercise.43 44 50 However, although these lifestyle modifications are known to at least moderately reduce BP if practiced regularly, adherence to such lifestyle regimens tends to be low over the long term.51 If overeating and alcohol misuse represent maladaptive attempts to cope with stress, then difficulties in altering such behaviors over the long term without enhancing underlying psychosocial well-being would not be surprising.52 53 54 In contrast, at least over the short term, compliance with the stress-reduction techniques studied here was quite high—97% for TM and 81% for PMR.
Possibly the most clinically relevant finding of these subgroup analyses was that BP reductions through the TM program, and to a lesser degree PMR, generalized across a wide range of risk conditions. Despite substantial differences in hypertension risk patterns, both African American men and women showed significant decreases in BP. Also, the high risk subgroups—ie, subjects who were psychologically distressed, obese, or physically inactive; used higher amounts of alcohol; consumed high sodium relative to potassium; or were at high risk on multiple factors—appeared to benefit from these treatments approximately as much as the low risk subgroups. It is noteworthy that even on the multiple risk factor variable, which accounted for 26% to 29% of the variance in BP change, high combined risk subjects changed as much as low risk subjects through the TM technique. (It should be noted that in the regression model, the regression coefficient for each risk factor was in the predicted direction except for the physical inactivity variable. Contrary to findings with other populations,50 higher physical activity was associated with an increase in BP in this minority elderly sample. Nevertheless, because our regression model was empirically derived, this variable was included. This made little difference in the outcome, however, because when the physical inactivity variable was excluded from the model, the BP differences between [and within] treatment groups remained essentially the same. The unexpected direction of association between physical inactivity and BP change may have been an artifact of the measure used and should be investigated more thoroughly in future studies.) The only exception was that DBP changed less in obese than in nonobese TM subjects. DBP nevertheless decreased significantly in obese TM subjects compared with EC subjects. In contrast, within the EC group, high risk subjects for most of the risk variables, including the multiple risk variable, significantly increased in BP relative to low risk subjects even over a 3-month period. This suggests that stress reduction may be most useful for preventing the progression of hypertension and subsequent cardiovascular disease in those who are at greatest risk.
The Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure (JNC V) recognized the contributions of sex, obesity, physical inactivity, alcohol consumption, dietary sodium, and psychosocial stress to the risk for hypertension and subsequent cardiovascular disease.25 The report also recommended lifestyle modification for all hypertensive individuals as either monotherapy or adjunctive therapy. JNC V additionally recommended that lifestyle modification be targeted to the particular behavioral disorder (eg, weight reduction for obese hypertensive individuals). Although the present findings do not negate these recommendations, they do suggest that stress reduction, at least with the TM technique, may be sufficient to reduce BP in older African Americans displaying various risk profiles.
Although JNC V acknowledged the contribution of stressors to hypertension, it questioned whether stress-reduction techniques have been shown to reduce or prevent high BP. One reason for the apparent disparity between our particular findings and their general conclusion is that JNC V did not focus on potential differences in the effects of specific approaches to stress reduction. Their conclusions were based on a narrative (ie, nonquantitative), selective review that emphasized the results of two prior randomized trials showing that muscle relaxation (in combination with one or more other stress-management approaches) did not significantly lower BP compared with controls.55 56 In contrast, the current study showed differential effects for TM compared with both PMR and EC. Thus, our data support the hypothesis that stress-reduction approaches are not homogeneous in their effects; that is, different techniques may produce different effects on BP, as well as on other clinical outcomes. Our findings are consistent with recent quantitative meta-analyses indicating that the TM technique is associated with effects approximately twice as large as found with other approaches—including PMR, other forms of muscle relaxation, electromyographic biofeedback, and techniques explicitly devised to induce a "relaxation response"—for chronic anxiety,18 poor self-esteem,19 and alcohol misuse,17 controlling for the strength of experimental design.
It is unlikely that changes in BMI, exercise, and dietary sodium-potassium accounted for the BP reductions in the present study because (1) subjects with low levels of these risk conditions at baseline showed BP reductions similar to those in subjects with high risk levels, and (2) other data from this study indicate that these factors did not change significantly over the 3-month period.57 With regard to changes in alcohol use, consumption did significantly decline among alcohol users in the TM group (by 6.5 and 4.6 drinks per week compared with EC and PMR, respectively), and this may have contributed to the decrease in BP in the alcohol users. However, the TM nonusers of alcohol also showed significant BP reductions, indicating that other mechanisms are likely to be involved.
With regard to psychosocial stress as a mechanism for the effects of stress reduction on BP, the finding that the subjects in low stress subgroups also showed significant declines in BP does not preclude the possibility that people who perceive that they are low in stress can still experience further declines in BP. Indeed, it was found that for the subjects who reported fewer stressful problems at baseline (as determined by median split), there was still a significant decline on the psychosocial stress factor for TM subjects compared with EC and PMR subjects combined. Decreased stress as a mechanism was also supported by the finding of a significant decrease on a second psychosocial factor, termed perceived health, in TM subjects compared with EC and PMR subjects combined. This factor was composed of total scores on three measures of perceived physical and mental health (see "Measures") that have been shown in the literature to be stress related.58 59
Thus, a decrease in psychosocial stress appears to have contributed to the effect of the mental technique on BP. From the perspective of the Maharishi Vedic Approach to Health, of which the TM technique is a key part, stress itself arises from a lack of integration of major physiological systems with the holistic "inner intelligence" of the body.20 This lack of integration from a contemporary perspective would appear to correspond to alterations of homeostatic mechanisms that have been related to hypertension.52 54 A growing body of research suggests that such alterations may be corrected or prevented through the TM technique, as indicated by decreased sympathetic activation,54 60 decreased hypothalamic-pituitary-adrenocortical activation,52 54 enhanced neurophysiological function,61 62 63 and enhanced serotonin metabolism.53 54 Such global physiological changes may have contributed to the reduction in BP seen across all sex and risk factor subgroups. Alternatively, there may be a different physiological mechanism specific to each risk subgroup. Further research to investigate the mechanisms for BP reduction in such diverse subpopulations is warranted.
Future studies also will be necessary to confirm and extend the current findings on the generalizability of these stress-reduction approaches, especially the TM technique, for the treatment of hypertension in diverse risk subgroups. Design features to incorporate in future research include longer-term follow-up of at least 1 year, larger subgroup sample sizes, assessment of additional objective risk factors (eg, sodium and potassium excretion, family history of hypertension, renin subtyping), stratification on key demographics before randomization, comparison with other lifestyle-modification approaches, and inclusion of other ethnic groups.
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Selected Abbreviations and Acronyms |
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Acknowledgments |
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This work was supported by grants from the Retirement Research Foundation (Nos. 88-95 and 88-96), Chicago, Ill, and the Lancaster Foundation, Bethesda, Md. Preparation of this manuscript was supported in part by National Institutes of Health grant 5R01HL-48107. Transcendental Meditation and TM are service marks registered in the US Patent and Trademark Office licensed to Maharishi Vedic Education Development Corp and used under sublicense. The authors are grateful to the following individuals for their helpful advice and/or editorial comments: Brian Hofland, PhD; R. Keith Wallace, PhD; David Orme-Johnson, PhD; Robert Cooper, MD; Carolyn Gaylord King, PhD; and for technical assistance, Linda Heaton.
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Footnotes |
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Reprint requests to Charles N. Alexander, PhD, Center for Health and Aging Studies, Maharishi University of Management, FB 1028, Fairfield, IA 52557-1028.
Preliminary portions of this study were presented at the Society of Behavioral Medicine, San Diego, Calif, March 22-25, 1995, and at the Centennial Conference of the National Medical Association, Atlanta, Ga, July 29 to August 3, 1995.
Received October 3, 1995;
first decision October 27, 1995; first decision February 21, 1996;
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