Animal research has demonstrated that physical activity encourages neurogenesis in the hippocampus's dentate gyrus, while human studies have demonstrated that it increases cerebral blood volume in the region. It has been shown that the volume of the hippocampal cortex predicts the progression of MCI into Alzheimer's disease. In animal studies, physical exercise has also been demonstrated to support neuronal survival following neurotoxic injury and neural functional recovery after ischemic insult. Circulating IGF-I (insulin-like growth factor), a potent neurotrophic factor that is suppressed by the administration of an antibody in mice, is one possible mediator of these effects. Exercise's protective impact against brain injury is then rendered ineffective. More generally, cerebral blood flow has been shown to increase and age-related cortical atrophy has been shown to decrease with cardiovascular fitness.
Although not in all studies, physical exercise is linked to a lower incidence of Dementia in observational studies of those without Dementia and those who have MCI. According to a meta-analysis of 21 longitudinal cohort studies on physical activity and dementia risk, persons without Dementia who engaged in more physical activity had a 14% reduced chance of developing Dementia than those who were lazy. Higher levels of physical exercise were also found to be protective against cognitive deterioration in a meta-analysis of 17 longitudinal cohort studies. It should be highlighted that a variety of studies were reviewed, with follow-up intervals for Dementia ranging from 1 to 26 years and for cognitive decline from 1 to 21 years.
According to the available research, it is unclear if one type of physical activity—aerobic versus weight training versus stretching/toning exercises like yoga or tai chi—is superior to another in terms of lowering dementia risk. Despite the overall suggestive nature of the evidence from prospective research, reverse causality is still a possibility. Following the onset of Dementia, physical deterioration and alterations to motor function are typical side effects of disease pathogenesis. Temporality must be clearly proven before physical inactivity may be considered a potential modifiable causal factor for Dementia. Furthermore, there is proof that a reduction in gait speed can occur up to 7 years before dementia symptoms appear.
Before Dementia or even MCI is diagnosed, there may be a preclinical prodrome that includes decreased physical activity. The association between the risk of Dementia and physical activity may also be complicated by other elements, such as genetic elements that may be protective or causative, or environmental elements like vitamin D levels and sunlight exposure. Nevertheless, a twin study in a Finnish population indicated that engaging in intense physical exercise was associated with lower risk of Dementia in later life after controlling for some of these potential causes or protective genetic variables. In a similar vein, a New York study discovered that MeDi and physical exercise were both independently linked to a lower risk of AD.
Mixed results have been seen in RCTs of physical activity treatments in persons with intact cognitive function. There were no differences in the cognitive outcomes between the groups in Lifestyle Interventions and Independence for Elders (LIFE), a randomised controlled trial (RCT) of 1635 older sedentary adults who were randomly assigned to either 24-months of moderate-intensity physical activity (walking, resistance training, and flexibility exercises) or health education. Smaller RCTs have discovered beneficial effects of weight training and aerobic exercise on cognition. The EXERT trial, a current study, is evaluating the effects of physical activity on cognition, functional status, brain atrophy, blood flow, and CSF biomarkers of AD. It randomly assigns 300 participants with mild memory issues and functional impairment (CDR 0.5) to either a moderate-to-high intensity aerobic training programme or a control group.
A recent AHRQ systematic review found that there is positive but inconclusive evidence that physical activity may prevent or decrease age-related cognitive decline based on an assessment of 19 RCTs categorized as having low or medium risk of bias. Despite intriguing links found in observational studies, it was also decided that there is inadequate evidence to say whether increasing physical activity prevents, delays, or slows MCI or clinical Alzheimer's-type Dementia. It's also important to note that just 18 of the RCTs in the review had a long duration (lasting 1 year or less). More research is needed that focuses on populations with intact cognitive function, includes longer follow-up, and makes a clear distinction between various types of physical activity.