A Cochrane review [Abstract] 1 included 29 studies, with eight weeks to five years follow-up, with a total of 1 602 subjects. Meta-analysis indicated that relaxation resulted in small, statistically significant reductions in systolic blood pressure, SBP (mean difference MD -5.5 mmHg, 95% CI -8.2 to -2.8) and diastolic blood pressure, DBP (MD -3.5 mmHg, 95% CI -5.3 to -1.6; 25 studies, n=1198) compared to control. The 9 trials that reported blinding of outcome assessors found a non-significant net reduction in blood pressure (SBP mean difference -3.2 mmHg, 95% CI -7.7 to 1.4, n=498) associated with relaxation. The 15 trials comparing relaxation with sham therapy likewise found a non-significant reduction in blood pressure (SBP mean difference -3.5 mmHg, 95% CI -7.1 to 0.2, n=564). The authors state that some of the apparent benefit of relaxation was probably due to the non-specific effects of treatment, such as frequent contact with treatment providers.
Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment and blinding) and by inconsistency (variability in results across studies). The combined sample was too small and the trials were too short-term to assess whether relaxation could reduce the risk of death, heart attack or stroke.
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