Sleep and physical activity as modifiable risk factors in age-associated cognitive decline

The number of older adults over the age of 65 is rapidly increasing. This change in demographics will not only increase the prevalence of chronic medical issues, but also result in higher rates of age-associated cognitive decline. Mechanisms for age-related cognitive decline are unclear, although many persons show Alzheimer's disease pathology, changes to cerebral blood flow, inflammation, and structural changes such as atrophy and increased white matter lesions. Increased levels of physical activity and exercise have been found to benefit older adults' cognitive functioning through changes in brain volume and cerebral blood flow. However, these studies are unable to explain the cognitive benefits of physical activity and exercise in the absence of improvement in brain structure or blood flow, suggesting other moderating factors. An unexamined factor that may link physical activity/exercise and cognition in older adults is improved sleep. Poor sleep has already been found to contribute to cognitive decline and to improve through increased physical activity or exercise in older adults. To date, few studies have examined the relationship among cognition, physical activity/exercise, and sleep. It is unknown if sleep is a moderator for the cognitive benefits of physical activity in older adults. This review proposes sleep as a potential moderator between cognitive function and physical activity/exercise by way of cerebral blood flow. Clinical implications and future areas of research will also be discussed.