This randomized controlled trial conducted with 1 year of follow-up extended the results of a previous independently conducted short-term follow-up study that compared the effects of different approaches to stress reduction on hypertension in African Americans during 3 months.25,26
The present trial evaluated a vital clinical question, that is, whether any of these lifestyle modification programs would remain effective in reducing BP during the relative long-term. The results of the present study support the feasibility and long-term efficacy of the use of a selected stress reduction approach in reducing BP in urban adult African Americans with stage 1 or 2 hypertension. During the 1-year duration of the study, the Transcendental Meditation program significantly decreased diastolic BP more than PMR or HE, and there was a trend for a greater reduction in systolic BP. Progressive muscle relaxation or HE did not differ from each other on any BP change comparison. Differences in compliance with treatment could not explain the results because when the BP results were adjusted for treatment compliance, the same pattern of results was found. In addition there was a significant reduction in antihypertensive medication use in the TM group compared to relaxation and education controls.
Although this study was not designed to evaluate gender differences in response to behavioral interventions, post hoc analysis of gender groups indicated that the TM group women had significantly greater reductions in both systolic and diastolic BP than women in both the relaxation and HE groups. These analyses showed that the women in the TM group had a significant reduction in systolic BP compared to both PMR and HE groups (−7.3 mm Hg v
0.7 mm Hg v
−0.7 mm Hg, respectively). These changes in systolic BP were somewhat similar to the reductions in systolic BP with these interventions reported earlier in the short-term study.25,26
The changes in diastolic BP in the three groups paralleled changes in the entire sample (−6.9 mm Hg v
−2.7 mm Hg v
−3.0 mm Hg for the TM, PMR, and HE women groups, respectively) with significant differences between TM and both PMR and HE. The greater reduction in systolic BP in the TM group women may have been related to lifestyle factors such as reductions in dietary sodium/potassium ratio or alcohol use. These effects remain to be confirmed and elucidated. The group of men in this study showed diastolic BP reductions of −4.7 mm Hg v
−3.1 mm Hg v
−2.0 mm Hg for TM, PMR, and HE, respectively, with a statistical trend for difference between TM and HE group men.
The magnitude of change for TM in diastolic BP within the overall sample group in the present study (−5.7 mm Hg) was similar to the previous short-term 3-month study (−5.7 mm Hg within group); however, there was a greater reduction in diastolic BP in the HE group in the present study compared to the previous trial (−2.6 mm Hg v
−0.8 mm Hg).25
Thus, the control-adjusted reduction in diastolic BP in the TM group was −3.1 mm Hg during 1 year of follow-up compared with control-adjusted change of −6.4 mm Hg after 3 months of follow-up in the previous study.25
In the short-term trial,25
TM decreased systolic BP more (−10.9 mm Hg within-group and −10.7 mm Hg control-adjusted) than the present trial (−3.1 mm Hg within-group and −2.2 mm Hg control-adjusted). The differences in results of the two independently conducted studies may have been due to one or more factors. As noted, the HE group showed a larger decrease in BP, suggesting the possibility of a more active lifestyle modification intervention. There was greater compliance in the previous study, 97% compared to 76% of the subjects in the present study regularly practicing the TM program. Also, the subjects in the current study were younger (ie, mean age 48.6 years v
66.6 years in the earlier study) and more likely to be in the workforce, which may have influenced compliance levels.
During the 1-year follow-up, the PMR and HE groups increased their use of BP medication compared to the TM group, which showed decreased antihypertensive medication use. These findings suggest that the effects of the TM program on reducing BP were not due to increased use of antihypertensive medication. The TM intervention also decreased BP at an earlier time period in the study compared to the other groups, with apparent differences by months 3 and 6. In contrast PMR and HE tended to reduce BP toward the end of the year but that effect may have been due to their increases in the use of antihypertensive medication. The long-term cost savings as well as prevention of adverse effects from drug therapy of using an effective nonpharmacologic approach such as the TM program are likely to be substantial from a public health perspective.38,39
The design of the present study addresses several methodological weaknesses identified in the literature.20
These include: 1) lack of adequate number of baseline BP measurements to control for habituation and regression to the mean; 2) lack of rigor in designing control treatments, balance of baseline characteristics, randomization, and blind data collection; 3) lack of comparison among different stress reduction techniques in the same experiment; 4) inadequate sample size; 5) inadequate length of follow-up; 6) medication changes not controlled or not carefully monitored; and 7) inadequate selection of appropriate patients for likelihood of response.
The validity of these results is supported by a randomized, single-blind design and multiple BP measures that were taken during five baseline visits. Regression to the mean was also statistically controlled by using pretest baseline systolic and diastolic BP as covariates in their respective analyses. The use of two stress reduction approaches in the same experimental setting allowed control for nonspecific intervention effects, with both active control groups given similar expectancy of benefits, attention from trainers, and time allowed for daily practice. External validity was enhanced by conducting the trial in a primary care center in a large inner city African-American community. The results could not be attributed to any of the pretest and demographic variables because the groups did not significantly differ on any of these variables.
It is unlikely that the results of this study could be due to attrition, as the intent-to-treat analyses yielded similar conclusions as analyses based on subjects who completed follow-up. Also, the attrition rates in each treatment group were similar. The reduction in high BP observed in the current study with the TM program were consistent with findings reported in previous randomized controlled trials in older and younger subjects using clinic BP25,26,40
or ambulatory BP measurements.41,42
Previous studies in adults, older adults, and adolescents have reported that PMR practice is associated with modest reductions in BP.20,43,44
These findings are somewhat similar to reductions found with PMR, particularly for diastolic BP, in the current trial. The general approach of PMR is to reduce muscular tension and thereby induce psychophysiological relaxation.36,45
There is some evidence for acute reductions in salivary cortisol, heart rate, and state anxiety with PMR practice.46
Meta-analyses have found evidence for the usefulness of PMR in insomnia and headache.47–49
However, a range of neurophysiologic stress changes reported for TM practice (eg, increased electroencephalographic coherence, cerebral blood flow, reductions in respiratory activity, alterations in a range of neuroendocrine stress markers, reductions in sympathetic nervous system tone, and increases in parasympathetic tone50,51
have generally not been reported for PMR practice. A meta-analysis, which directly compared effects of PMR to those of TM on anxiety reduction, found almost twice the effect size for TM.52
However, few studies have previously assessed the effects of both interventions in the same experimental setting.
A systematic review of meta-analyses of behavioral stress reduction approaches suggests that the TM technique may be distinctively effective in modifying several clinically relevant physiological and psychological outcomes.22
This is consistent with meta-analyses of the effects of behavioral stress reduction methods on BP, which indicate a heterogeneity of effects of various stress reduction techniques.20,21
These latter findings may contribute to an explanation of the differential effects on BP of TM and PMR behavioral interventions observed in the present study.53
Reductions in BP of the magnitude seen in the present study were similar to and sometimes greater than BP reductions reported in systematic reviews of other lifestyle modifications for hypertension. For example, the most recent review of clinical trials on long-term effects of dietary sodium intervention reported that the average reductions in systolic and diastolic BPs were −2.5 mm Hg and −1.2 mm Hg for intermediate-term follow-up of 6 to 12 months.54
For long-term follow-up of 13 to 30 months, the BP reductions were −1.1 mm Hg systolic and −0.6 mm Hg diastolic. Hooper et al54
concluded that intensive dietary sodium interventions were “unsuited to primary care or population prevention programs, provide only small reductions in BP and sodium excretion, and effects on deaths and cardiovascular events are unclear” (pg. 628). Meta-analysis of trials on aerobic exercise reported reductions in BP of −3.84 mm Hg systolic and −2.58 mm Hg diastolic during a median duration of 12 weeks.55
However, by 24 weeks or longer, the average systolic BP reduction was −2.0 mm Hg with no significant change in diastolic BP.55
Systematic review of randomized controlled trials (RCTs) with interventions lasting longer than 6 months in adults aged 45 years or more with hypertension found no significant changes in BP with aerobic exercise.16
In terms of weight loss, a meta-analysis reported that when antihypertensive drug regimens did not vary, loss of approximately 5 kg of weight reduced BP by −3.0 mm Hg systolic and −2.9 mm Hg diastolic.56
Two subsequent RCTs reported that weight reduction of 2 to 4 kg reduced systolic BP by about −1 mm Hg during 1 to 3 years of follow-up.57,58
A systematic review on RCTs on effects of moderating alcohol consumption found reductions of −3.3 mm Hg systolic and −2.0 mm Hg diastolic among fairly heavy, predominately male alcohol drinkers (≥ 3 drinks/d) for a median of 8 weeks follow-up.
The results of change in BP in the present study are clinically significant. For example, even a 2 mm Hg reduction in diastolic BP would be associated with a 17% decrease in the prevalence of hypertension, 6% reduction in risk for CHD, and 15% reduction in risk for stroke and transient ischemic attack.59
Slightly larger CVD preventive effects have been calculated from antihypertensive clinical trials and major prospective observational studies.10,60
Mechanisms through which TM practice reduces BP may be via reductions in acute and chronic sympathetic nervous system tone37,61,62
and possibly modification of other neuroendocrine and neurophysiologic mediators of stress.37,63
In addition, long-term practice of the TM program has been associated with reductions in other cardiovascular and behavioral risk factors (eg, oxidized lipids,64
and psychological well-being), which may contribute to hypertension and CVD risk.66
Studies on effects of the TM program on CVD surrogate end points, morbidity and mortality, have reported regression of carotid atherosclerosis,67
reduced myocardial ischemia,68
and lower mortality rates.
Particularly relevant to the mechanisms of effects of the TM program on hypertension are the results of studies suggesting restoration of adaptive mechanisms.37,63,70
Adaptive mechanisms involve the autonomic nervous system, neuroendocrine axes, and the cardiovascular system and result in physiological adaptability and stability during stressful events.71
These mechanisms are altered by chronic stress leading to physiologic disorder including CVD.71,72
Allostatic load is the term applied to the pathophysiologic set of alterations of these adaptive mechanisms.71,72
From the perspective of the traditional Vedic system of natural health care from which the TM program originates, this approach enhances an integrated set of endogenous homeostatic and self-repair biochemical and physiologic mechanisms traditionally called the body’s inner intelligence.31,33,73
It has been proposed that the effects of the TM program on adaptive mechanisms are consistent with reduction of allostatic load.37,39
In conclusion, the present clinical trial suggests that a selected stress reduction approach, the TM program may be effective in reducing hypertension in African-Americans adults when used as an adjunct to usual care, at least during 1 year. Finally, the results of this trial suggest that all techniques of stress reduction do not have the same effects, consistent with the results of several meta-analyses and previous randomized trials.22,25,65,66,74
These data contribute to bridging the gap between biomedical and biobehavioral research and medical practice.75