This is the largest, most carefully controlled trial of yoga in seniors conducted to date. The trial demonstrated that a 6-month yoga program did not produce any improvements in cognitive function. There were significant improvements in quality-of-life measures. There were also significant improvements in outcome measures specifically related to the intervention (eg, one-legged standing and seated forward-bending ability).
The subjects in the yoga and exercise intervention did not do better than the wait-list control group on the cognitive outcome measures, but this finding must be interpreted cautiously. Though exercise interventions in animals have been reported to show benefits to brain function and structure,47
the effect of a short-term randomized exercise intervention exercise on cognitive function in healthy seniors is not large, with the differences perhaps related to the intensity of the exercise intervention. Although most cross-sectional studies have suggested exercise is beneficial to cognitive function,48–51
data from exercise intervention studies are less clear.52,53
There have been several intervention studies with clear improvement in VO-2 max (ie, maximal rate of oxygen consumption) or other physiologic parameters, mood, and quality of life without a clear improvement in cognitive function.54,55
Additionally, exercise intervention may improve only certain aspects of cognitive function.56–58
Healthy seniors such as those who volunteered for this study may be functioning near their best and may not be able to demonstrate significant improvement during a 6-month study. This may contrast with seniors who are potentially not at their best—beneficial effects from exercise interventions in seniors with depression have been more consistent.59,60
The improvements in physical measures directly related to the yoga intervention are not surprising. Yoga practice involves training on poses very similar to these outcome measures. One-legged balance may have some health implications, such as risk of falls, and has been shown previously to be improved in healthy older people practicing tai chi, another mind-body technique of which balance exercises are a component.61,62
Though this study did show that yoga produced beneficial effects on quality-of-life measures, the mechanism of action of these improvements may not relate directly to the yoga. Socialization, placebo, and self-efficacy effects are other potential mechanisms. The exercise group controlled for socialization to some degree, but there was less of a class format in the exercise group. At least 1 previous study has suggested that exercise-related improvements in stress were secondary to class participation and not to improvements in fitness.63
Future yoga intervention studies will need to carefully control for the class aspect that may be beneficial to everyone, but especially seniors. There is also likely some placebo effect related to the yoga intervention. One group has already shown that psychological benefits of an aerobic exercise intervention in a group of healthy young adults could be increased simply by telling subjects that the exercise program was specifically designed to improve psychological well-being.64
The placebo effect, expectancy, and self-efficacy may have a significant impact65,66
and are difficult to adequately control for in behavioral interventions that are necessarily non-blinded. Even reported cognitive improvements related to transcendental meditation may be related to expectancy of subjects recruited for trials.67
Although there were many secondary outcome measures, we do not believe the findings are simply random results from multiple comparisons. The P value for the intervention effect on one of the SF-36 subscales was sufficiently low that it would have been significant even with a very conservative Bonferroni correction. However, these were secondary outcome measures, so these findings should be considered preliminary. Also, given power issues and size, the absence of statistically significant effects on the mood measures needs to be interpreted conservatively, and there remains a possibility that mood improvements contributed to these improvements in quality of life and fatigue. For example, given the correlation coefficient for baseline and 6-month CESD-10 of 0.4, the study was powered at only 0.8 to detect an effect of about 1 point.
Regarding the lack of effect on quality-of-life measures in the exercise group, most other randomized exercise intervention studies included only seniors who were consistently more sedentary than those in this study. Because the exercise class was primarily serving as a control group for the yoga intervention, we allowed subjects at entry to be doing aerobic exercise up to 3.5 hours per week (30 minutes per day). The seniors were more physically active at baseline than were subjects with multiple sclerosis in a concurrently performed 3-armed yoga and exercise intervention study in which the exercise intervention produced improvements in fatigue and quality of life comparable to those produced by yoga.23
In that study, there were also no effects on the cognitive outcome measures from either intervention. The exercise class in the current study was just once per week, in contrast to more frequent classes in most other exercise intervention studies in seniors.60,68
Additionally, in this study, the yoga intervention was considered more desirable by many of our participants, so there may be effects related to disappointment and expectancy, as well.
There are many issues related to design of a yoga or exercise intervention that are significantly different from the usual drug study and may affect generalizability. For future trial planning, these are mentioned briefly. Class scheduling logistics needed to address the issue of preferred times for each cohort of subjects. The yoga class was adapted for beginning seniors; thus, the results of this study may not be directly generalizable to a typical community yoga class. The other potential issue related to generalizability is that our subjects were a highly motivated group that was willing to volunteer for a research study. Subjects are necessarily non-blinded for these interventions, and there was a significant discussion at the time informed consent was obtained about the randomization process and the need for subjects to accept the randomization. Even with this measure, several subjects dropped out, probably because of disappointment with their randomized group assignment.
Healthy seniors participating in a 6-month yoga or exercise class showed no differences in cognitive function compared to a wait-list control group. The yoga intervention produced improvements in quality-of-life measures not seen in the exercise group and also improvements in physical measures related to the intervention itself (eg, timed 1-legged standing and forward-bending flexibility). The lack of effect on cognitive function does not necessarily imply that yoga or aerobic exercise is not beneficial to cognition but may relate to ceiling effects in this relatively healthy group of seniors or the relatively short intervention period of the study.