Physical activity and dementia risk – the evidence

There is growing evidence that physical activity may protect against cognitive decline and dementia in old age.

Several longitudinal studies have found that older people who exercise are less likely to experience cognitive decline or develop dementia.  For example, exercising at least 3 times per week in people over age 65 was associated with a 38% reduced risk of developing dementia after 6 years follow up [1].  In a randomised controlled trial of people aged 50 and over with subjective memory impairment, a 6 month program of physical activity resulted in improved cognition at the end of the trial and after 18 months follow up [2].

Regular exercise during midlife may also protect against later developing dementia.  In one study, exercising at least twice a week at midlife was associated with a 52% reduced risk of dementia at age 65-79 [3].

Several mechanisms have been proposed to explain the association between physical inactivity and cognitive decline [4,5].

• Inactivity increases the risk of vascular disease and vascular risk factors.  Vascular disease, in turn, increases the risk and severity of cognitive decline and dementia.
• Inactivity is associated with higher levels of inflammatory markers in the blood (e.g. C-reactive protein).  Inflammation has been associated with an increased risk of cognitive decline and dementia.
• Physical activity appears to stimulate neurogenesis, providing another pathway by which physical activity could protect against cognitive decline and dementia.

Regular physical exercise provides a range of health benefits.  The evidence supporting the beneficial effects of physical activity on brain health provides yet more reasons to encourage regular physical activity among people of all ages.

Additionally, there is a body of evidence that brief interventions in primary care practice can be effective in increasing the physical activity levels of patients [6].

References

1. Larson EB, et al. Exercise is associated with reduced risk for incident dementia among persons 65 years of age and older. Ann Intern Med, 2006, 144:73-81.
2. Lautenschlager NT, et al. Effect of physical activity on cognitive function in older adults at risk for Alzheimer’s disease. JAMA, 2008, 300:1027-1037.
3. Rovio S, et al. Leisure-time physical activity at midlife and the risk of dementia and Alzheimer’s disease. Lancet Neurol, 2005, 4:705-711.
4. Jedrziewski MK, et al. Physical activity and cognitive health. Alzheimers Dement, 2007, 3:98-108.
5. Hendrie HC, et al. The NIH cognitive and emotional health project. Report of the critical evaluation study committee. Alzheimer’s & Dementia, 2006, 2:12-32.
6. The Royal Australian College of General Practitioners. Physical activity. Policy endorsed by the 50th RACGP Council 9 February 2008. South Melbourne: RACGP, 2008.