Clinical trials clarify role of exercise in cognitive function and dementia
Four studies reported at the Alzheimer's Association International Conference 2012 describe the ability of targeted exercise training to promote improved mental functioning and reduced risk for cognitive impairment and dementia in cognitively healthy older adults and those with mild cognitive impairment (MCI).
The reports, from six- and 12-month randomized, controlled clinical trials, depict the beneficial effects of different types of exercise—resistance training, aerobic training and balance-stretching training—on a variety of cognitive abilities, brain structure, functional neural plasticity, growth factors and risk factors for cognitive decline such as depression and sleep quality.
"Currently, the strongest data for lifestyle-based Alzheimer's risk reduction is for physical activity, yet this data is generally observational and considered preliminary, said William Thies, Ph.D., Alzheimer's Association chief medical and scientific officer. "These new intervention studies are taking place over longer periods of time to begin to clarify exactly which types of physical activity are most effective, how much needs to be done, and for how long. In particular, where previously we had seen positive associations between aerobic activity, particularly walking, and cognitive health, these latest studies show that resistance training is emerging as particularly valuable for older adults."
"We need long-term studies in large, diverse populations, and we need the research funding to conduct those trials. For example, we have learned very practical lifestyle risk factors for heart disease from long-term research like the Framingham Study. Alzheimer's now needs its version of that research," Thies added.
Kirk Erickson, Ph.D., of the University of Pittsburgh and colleagues randomized 120 older adults without dementia who have been sedentary for the previous six months to a moderate intensity walking group or a stretching-toning group for one year. MRI was used to measure the size of a brain region associated with memory, known as the hippocampus, both before and after the exercise intervention. Blood was drawn to measure concentrations of brain-derived neurotrophic factor (BDNF), and a cognitive testing battery was conducted before and after the intervention.
The researchers found that, in this study group, one year of exercise training increased the size of the hippocampus by 2% in the walking group compared to the stretching-toning group. (Significant shrinking of the hippocampus is characteristic of Alzheimer's disease.) The increase in hippocampal volume was correlated with similar changes in BDNF.
"Our findings suggest that the aging brain remains modifiable, and that sedentary older adults can benefit from starting a moderate walking regimen," Erickson said.
Teresa Liu-Ambrose, Ph.D., PT, of the University of British Columbia and Vancouver Coastal Health Research Institute, was the principal investigator of the six-month, randomized controlled EXCEL (EXercise for Cognition and Everyday Living) study, which compared the effects of both twice-weekly resistance training (weight lifting) (n=28) and twice-weekly aerobic training (walking) (n=30) with twice-weekly balance and tone exercises (n=28) on executive cognitive function in women aged 70-80 with probable MCI.
Compared with the balance and tone group, the resistance training group significantly improved performance on the Stroop Test, which measures selective attention and conflict resolution, and a memory task. Resistance training also led to functional changes in three brain regions involved in memory. In contrast, the aerobic training group did not show similar improvements.
"MCI is a critical window to intervene against dementia," Liu-Ambrose said. "We found that twice-weekly resistance training is a promising strategy to alter the trajectory of cognitive decline in seniors with MCI."
Liu-Ambrose and colleagues at the University of British Columbia used multi-state modeling to investigate the simultaneous effect of exercise training and baseline factors on changes in executive cognitive function, and the effect of exercise training on an individual's probability for cognitive improvement, maintenance or decline.
They performed a secondary analysis of a 12-month randomized, controlled clinical trial conducted in Vancouver of 155 community-dwelling women 65 to 75 years old who were randomly assigned to either resistance training or balance and tone training. The primary outcome measure was performance on the Stroop Test.
They found the probability of improving or maintaining results of the test were higher with resistance training among the study participants with higher function at beginning of the study; resistance training and balance and tone exercises had similar effect among those with lower function at baseline; and overall, those in the balance and tone group demonstrated a significantly lower probability for improved performance on the Stroop Test, and a significantly higher probability of decline.
Hiroyuki Shimada, Ph.D., and colleagues at the National Center for Geriatrics and Gerontology in Japan conducted a randomized trial to test the impact of a 12-month, supervised, multicomponent exercise on cognitive function among older adults with amnestic (memory-related) MCI. The exercise program included aerobic exercise, muscle strength training, and postural balance retraining.
The study population consisted of 47 older adults with amnestic MCI, 65 to 93 years old. Participants were randomized either to multicomponent exercise (n = 25) or an education control group (n = 25). People in the multicomponent exercise group exercised under the supervision of physiotherapists for 90 minutes a day, two days a week, 80 times for 12 months. People in the control group attended three education classes about health during the 12-month period. Measurements of cognitive function (Logical Memory II subtest of the Wechsler memory scale-revised, letter and category fluency, digit symbol coding, and Stroop color word test) were administered after six and 12 months.
The scientists found the multicomponent exercise and educational program improved performance on Logical Memory II subtest of the Wechsler memory scale-revised. Additionally, there was a significant interaction effect for letter fluency test between groups.