Can aerobic exercise protect against dementia?

In 2005, in the US, 36 million persons were over 65. Strong evidence indicates that memory and other cognitive tasks start declining at age 50 [1]. Furthermore, in the US, the prevalence of dementia ranges from 5% to 10% [2,3] and that of mild cognitive impairment (MCI) ranges from 12% to 18% [4,5]. Cognitive decline is common in persons over 70 and has an important impact on quality of life. To improve the quality of life for older persons, it is imperative that we begin to understand which factors contribute to cognitive decline and brain atrophy. Furthermore, we need to determine which biomarkers or neurological measures can be used to predict these conditions and what therapeutic interventions can improve an individual's brain health. Recently, moderate exercise and improved fitness were shown to enhance cognition in cognitively normal older persons as well as in individuals who complain of memory difficulty [6].Additionally, fitness correlates with brain volume in persons who are cognitively normal [7] and in those with Alzheimer's disease (AD) [8]. In this paper, we shall discuss the following:1. The causes of cognitive decline in older persons and why exercise could be a broad-spectrum intervention for dementia.2. After this, we shall present epidemiological evidence that exercise may slow cognitive decline and decrease the chance of dementia.3. Then we shall discuss the randomized control trials that provide evidence that exercise has a positive effect on improving cognition.4. Following that, the paper will report the animal studies showing that exercise may be protective of the brain.5. Lastly, we shall discuss biomarkers, starting with imaging and moving onto telomeres, plasma measures, cerebrospinal fluid (CSF) measures, and inflammatory biomarkers.The three most common forms of dementia are AD, Lewy body disease (LBD), and vascular dementia (VaD) [9] and all contribute to cognitive decline and brain atrophy. Noting that mixed dementia (having overlappin