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Exercise is well known to be good for age-related brain health but, as of yet, the mechanism of these benefits is not understood. Physical exercise is associated with a reduced incidence of Alzheimer’s disease, the most common form of dementia (Buchman et al., 2012), and a sedentary lifestyle alone is believed to be responsible for over four million of these cases (Norton et al., 2014). 

Exercise can have benefits on cognition, and this is believed be a result of the physical activity positively influencing brain cell growth. Recently, a team in UC San Francisco has shown that when elderly people sustain levels of activity, they have higher levels of a type of protein which enhances the integrity of the connections between brain cells (also known as ‘neurones’) to prolong healthy cognition.

The brain is made up of approximately eighty-six billion neurones, all of which communicate with each other at junctions called synapses, where chemicals are released and travel across the gap to relay the message (also known as ‘firing’). Neurones form ‘networks’, in which they communicate with each other, as they become more mature, neurones form more synapses by extending branches or ‘dendrites’- when these branches are developing, factors to encourage their growth are required. Neuronal networks in adults are complex and this allows for complex cognitive processing such as recalling a memory or remembering how to perform an action.

In Dementia, plaques made from two types of protein form on the surface of the brain, these proteins are tau and amyloid. It is believed that amyloid accumulates first and then tau forms later on. Their aggregation interferes with synapses and causes them to deteriorate, thus interrupting communication within the brain’s networks. These actions are responsible for the cognitive decline seen in people with dementia.

Previous evidence had shown that physical activity was associated with increased synaptic strength, whether it was measured in the spinal fluid or brain tissue at autopsy and was proposed to interfere with the relationship that forms between amyloid and tau (Casaletto et al., 2017). However, a new study has proven that the number of proteins which maintain the integrity and functioning of synapses are increased in elderly people who stay active. Interestingly, these effects were not only found in the hippocampus (an area of the brain involved with memory) but also throughout other brain areas involved in cognitive function and processing (Casaletto et al., 2022). Maintenance of neurone and synapse integrity is vital to normal neuronal function and maintaining healthy cognition.

This revolutionary new study is the first to prove that synaptic protein levels are related to physical activity and propose a mechanism for how exercise exerts its protective effects on the brain. So whilst exercising may not be effective in preventing the initial onset of Alzheimer’s, it is likely a valuable tool in preventing the severity of the cognitive decline that accompanies it. This shows us how and why upholding a good routine of physical exercise in our daily lives could protect us from developing dementia in the future or experiencing cognitive decline.

References

Buchman, A. S., Boyle, P. A., Yu, L., Shah, R. C., Wilson, R. S., & Bennett, D. A. (2012). Total daily physical activity and the risk of AD and cognitive decline in older adults. Neurology, 78(17), 1323-1329.

Norton, S., Matthews, F. E., Barnes, D. E., Yaffe, K., & Brayne, C. (2014). Potential for primary prevention of Alzheimer's disease: an analysis of population-based data. The Lancet Neurology, 13(8), 788-794.

University of California - San Francisco. "Exercise alters brain chemistry to protect aging synapses: Enhanced nerve transmission seen in older adults who remained active." ScienceDaily. ScienceDaily, 7 January 2022. www.sciencedaily.com/releases/2022/01/220107100955.htm

Casaletto, K. B., Elahi, F. M., Bettcher, B. M., Neuhaus, J., Bendlin, B. B., Asthana, S., ... & Kramer, J. H. (2017). Neurogranin, a synaptic protein, is associated with memory independent of Alzheimer biomarkers. Neurology, 89(17), 1782-1788.

Kaitlin Casaletto, Alfredo Ramos‐Miguel, Anna VandeBunte, Molly Memel, Aron Buchman, David Bennett, William Honer. Late‐life physical activity relates to brain tissue synaptic integrity markers in older adults. Alzheimer's & Dementia, 2022; DOI: 10.1002/alz.12530