Aerobic exercise improves cognition in older people
A randomised controlled trial from Australia has provided further evidence that aerobic exercise can improve cognitive function in older adults.
A total of 170 volunteers with subjective memory impairment, but no dementia, were randomly allocated to either a 24-week physical activity intervention or education and usual care. At 6 months, participants in the intervention group were walking about 9,000 steps a week more than those in the usual care group.
Cognitive function was assessed using the Alzheimer Disease Assessment Scale (ADAS-Cog). At the end of the intervention, the average scores for the exercise group had improved by 0.26 points whereas the scores for the usual care group had deteriorated by 1.04 points: a difference of 1.3 points. Twelve months after the end of the intervention, participants in the exercise group were still walking approximately 6,000 steps a week more than the controls and their ADAS-Cog scores were on average 0.69 points better.
Is this clinically significant? The authors refer to data from an independent sample of older adults with subjective memory impairment which showed an average annual decline of 3.5 points (compared with up to 5 points a year in patients with mild dementia).1 The 0.69 point advantage of the exercise group at the end of the follow-up period would therefore equate to a delay of only two months in the progress of cognitive decline.
However, an important limitation of the ADAS-Cog is that it does not measure attention and executive function.2 Kramer and colleagues randomised 124 previously sedentary older adults to a 6-month training programme of either aerobic (walking) or anaerobic (stretching and toning) exercise. At the end of the intervention, participants from the walking group performed significantly better on tests of executive function such as task switching but not on other cognitive measures.
A meta-analysis of 18 randomised intervention studies found that fitness training had a moderate beneficial effect on cognitive function in older adults without dementia (effect size 0.48).3 Again, the largest improvements were seen in executive control processes. A similar beneficial effect has been reported in dementia patients (effect size 0.57).
Cross-sectional studies have found an inverse relation between fitness levels and brain volume in older adults. Kramer and colleagues found that participants from their aerobic training group had a significant increase in grey matter volume in regions of the frontal and superior temporal lobes, compared with the stretching and toning controls. Their improved performance on a focussed attention task was associated with increased blood flow to the frontal and parietal regions which modulate attention.
The National Dementia Strategy is to recommend training for GPs in the recognition of early signs of dementia. This is based on evidence that earlier provision of home support and carer support can reduce admissions to care homes.4 However, we face the problem that, having made an early diagnosis of dementia, we have no treatment to offer which can alter the progression of the disease. A prescription for walking would be an attractive option, but it is not yet clear whether this can achieve a clinically significant effect.
Lautenschlager NT, Cox KL, Flicker L et al. Effect of physical activity on cognitive function in older adults at risk for Alzheimer disease. JAMA 2008;300:1027-37.
Erickson KI, Kramer AF. Aerobic exercise effects on cognitive and neural plasticity in older adults. Br J Sports Med 2008. doi:10.1136/bjsm.2008.052498.
Dr Phillip Bland