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Introduction
There is considerable interest in the potential modification of the relative risk for developing dementia and its preclinical syndromes such as mild cognitive impairment (MCI). Dementia represents a substantial health, social, and economic burden in developed countries such as Australia, with estimates of over 245,000 Australians, or approximately 1.1% of the population, currently living with dementia. Despite difficulties in diagnosis, dementia is the leading cause of disability in adults older than 65 years (Access Economics, 2009). With the demographic passage of the "baby boomer" generation coupled with increased life expectancy, it has been predicted that by 2050 the incidence and frequency of dementia will increase dramatically with approximately 940,000 Australians, or 2.8% of the population, having dementia (Deloitte Access Economics, 2011). In 2002-2003, a total of AUS$3.85 billion or 4.5% of government health and aged care spending was expended on dementia (Access Economics, 2009). It is estimated that by 2060, health spending on dementia will be greater than that for any other health condition, with projected costs of AUS$83 billion or 11% of the expenditure in the entire health and residential aged care sector (Access Economics, 2009). Dementia has recently been identified by the Australian Government as a national health priority. It has furthermore been estimated that delaying the onset of dementia by just a few months will produce future health savings in the order of billions of dollars by mid-century (Access Economics, 2004). Hence, strategies that delay dementia onset, and/or increase resistance to aging-related cognitive decline, would have significant health and economic benefits.
Age-related decline in cognitive function, most notably information processing speed, attention, concentration, and memory performance, has been well described (Salthouse et al., 1996; Bisiacchi et al., 2008; Johnson et al., 2009). Other studies indicate that pathological changes to the brain are also associated with aging, with progressive cortical shrinkage, reduction to gray matter volume in several regions, and white matter loss in the prefrontal cortex being documented (Beason-Held et al., 2008). Despite the evidence of these age-related changes to the function and structure of the brain, considerable variability is observed across individuals of approximately the same age and in the presence of brain structural changes that appear similar in...