Exercise and Brain Aging
The brain is a pliable organ. Its pliability makes it versatile – allowing the body to easily respond to the external environment and at the same time permit a variety of other cognitive as well as emotional and motor functions. But, over time, it ages like the rest of us.
A child's brain is most malleable. The brain, in fact, grows dramatically in size during the childhood years, as shown by the rapid gains in intelligence of a child. Brain volume begins to diminish at age 30.
Similar to an automobile, the apparent health of the human brain and its maximal efficiency also depend on a lot of factors. The most profound among them is the presence of aerobic activity, or to put it more simply, exercise. According to recent studies, exercise greatly affects brain aging by slowing cognitive decline. Studies like this can be revolutionary for neurodegenerative diseases such as Alzheimer's disease.
How does aging affect the brain?
As I've already said, by age 30, the brain begins to shrink. This happens gradually but eventually increases its pace by age 60 or 70.
The diminishing size is brought about by the enlargement of the lateral ventricles and widening of the brain sulci which later on will present with neurological deficits, as in the form of degenerative diseases. Most noticeable also is the atrophy of the limbic system, which is largely responsible for memory. The pace of atrophy, however, is minimized with healthier, older individuals in contrast to individuals with Alzheimer's disease. By the age of 70, a significant decrease in the number of neurons will be noted, particularly in the neocortex. Neuronal loss can also be seen in other parts of the brain, such as the locus ceruleus, substantia nigra and also the nerve cells and myelinated fibers of the spinal cord. These losses are subtle, occurring minimally by the decade. However, this process accelerates by age 60.
A study explained that verbal intelligence begins to decline very gradually by the age of around 60. Profound age-related effects are seen with learning, memory, and problem solving. These might be due to the slowing of the speed in analyzing information. By age 70, the ability to process, memorize, and obtain new data as well as focus and recall names diminishes. However, although recalling names and specific dates becomes difficult, the memory of the experience itself is preserved.
While all these observations are backed by solid data and years of research, it is still worthy to note that the effects of aging on mental abilities varies tremendously among individuals. Certain individuals in history such as Goethe, Picasso and Humboldt continued to be productive and creative until late in their lives. However, these personalities only continued works that had been started earlier on in their lives and no, or little, new work was started in older age. In these situations, the effects of old age may have been compensated by above average intelligence, stringent work environment, and certain personal lifestyles.
Motor and gait changes are the most obvious manifestations of the effects of aging. By age 30, agility begins to decrease, brought about by diminishing neuromuscular control. This can be seen especially in athletes who usually retire by age 35. Urinary incontinence is also seen in the aging population. The decline in gait brings about a more common occurrence of falls in the elderly. These are usually caused by worsening visual acuity and vestibular function.
The inability to compensate for the drastically changing posture in the elderly also causes the frequency of falls, often occurring while performing day-to-day activities such as walking and moving down the stairs. Age-related neurological diseases such as stroke and proteinopathies as seen in Alzheimer's disease can also cause both cognitive and motor impairments in the elderly.
How does exercise affect the brain?
There have been various studies that indicate the beneficial effects of aerobic exercise to the brain. One study showed that greater physical activity in the elderly is associated with greater brain volume in the frontal, temporal, parietal lobes and the hippocampus, decreasing their risks for Alzheimer's-related dementia by 50%. Individuals who already have mild Alzheimer's-related cognitive impairment also showed increased brain volumes. A significant improvement in cortical connectivity and activation was observed in one study using functional brain MRI. In line with this, elderly individuals who are physically fit performed better in cognitive testing than their unfit counterparts with similar amounts of exercise.
Exercise also increases levels of Brain-Derived Neurotrophic Factor (BDNF). BDNF is predominantly seen in the brain but its values cannot be directly assessed. The circulating levels of BDNF in blood serum gives an approximate value of BDNF in the brain. BDNF has been widely studied in animals, indicating its role in neuroplasticity and against neuronal atrophy. A study has shown that BDNF level is decreased in individuals with Alzheimer's dementia. It is also observed that increased BDNF levels are observed in young, healthy individuals with short-term vigorous and long-term endurance exercise. This clearly suggests that younger individuals who are consistently active and do exercise or any form of sport have significantly decreased risk for developing dementia in their old age.
It is also important to note that certain lifestyles and genetic predispositions affect the normal aging process of the brain. A study has noted that increased total serum cholesterol in late middle-aged adults accelerates brain processes related to normal aging. Along with other factors, this increases the risk for development of Alzheimer's dementia. Exercise, therefore, is one way to minimize this risk.
Exercise can become a cost-effective prophylactic therapy for neurodegenerative diseases such as dementia and Alzheimer's. The type of exercise regimen does not matter as long as it suits the physical requirements and interests of the individual. Aside from the cognitive effects that can be brought about with exercise, beneficial effects can also be observed for cardiovascular and skeletal reasons. In general, routine physical activity in both young and old individuals is important factors in decreasing mortality rates and public burden. Nevertheless, more studies are needed to suggest specific interventions aimed at slowing down aging in the general population.
Ahlskog, J., Geda, Y., Graff-Radford, N., & Petersen, R. (2011). Physical Exercise as a Preventive or Disease-Modifying Treatment of Dementia and Brain Aging Mayo Clinic Proceedings, 86 (9), 876-884 DOI: 10.4065/mcp.2011.0252
Brown, B., Peiffer, J., & Martins, R. (2012). Multiple effects of physical activity on molecular and cognitive signs of brain aging: can exercise slow neurodegeneration and delay Alzheimer's disease? Molecular Psychiatry, 18 (8), 864-874 DOI: 10.1038/mp.2012.162
Raji CA, Merrill DA, Eyre H, Mallam S, Torosyan N, Erickson KI, Lopez OL, Becker JT, Carmichael OT, Gach HM, Thompson PM, Longstreth WT, & Kuller LH (2016). Longitudinal Relationships between Caloric Expenditure and Gray Matter in the Cardiovascular Health Study. Journal of Alzheimer's disease : JAD PMID: 26967227
Reiman, E., Chen, K., Langbaum, J., Lee, W., Reschke, C., Bandy, D., Alexander, G., & Caselli, R. (2010). Higher serum total cholesterol levels in late middle age are associated with glucose hypometabolism in brain regions affected by Alzheimer's disease and normal aging NeuroImage, 49 (1), 169-176 DOI: 10.1016/j.neuroimage.2009.07.025
Willey, J., Gardener, H., Caunca, M., Moon, Y., Dong, C., Cheung, Y., Sacco, R., Elkind, M., & Wright, C. (2016). Leisure-time physical activity associates with cognitive decline: The Northern Manhattan Study Neurology DOI: 10.1212/WNL.0000000000002582
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