On several occasions, I have written about the anti-aging beneficial effects of exercise. New studies, confirm earlier findings of exercise benefit. Now, a new study shows that exercise reduces levels of the major inflammatory chemical, interleukin-6, and an associated enhancement of neural activity in the brain circuitry used to encode information and form memories.
In response to earlier studies by others showing that exercise improves mental function, a team from mostly German universities studied the effects of exercise on 32 subjects aged 52 to 71 years old. They were particularly interested in memory because prior studies by others made it clear that age usually impairs memories of names and faces, situations and events, which are categorized as episodic memory. Tests of recall of episodic memory show marked age decrements in many subjects, even if they are given reminder cues.
Other researchers had shown that exercise, particularly aerobic exercise, reduces decline of episodic memory. This group of researchers wanted to explore why this benefit occurs. They examined two possibilities for the benefit of exercise:
1. Reduction of inflammatory chemicals (interleukin-6), which is known to occur with aerobic exercise in younger people, and
2. Strengthened connection among neurons that encode and form episodic memories (in the hippocampus, thalamus, and medial prefrontal cortex).
In the experiment on day one, subjects completed a survey that revealed each person's level of physical activity over the past week and gave a blood sample for measuring the baseline level of interleukin-6. Each subject then took several standardized tests of episodic memory. Then each subject had their brains scanned with fMRI while they were asked to memorize a series of faces and their association with a profession (pilot, electrician, bus driver, etc.). After the scan, they were tested for recall. The purpose of the scan was to assess functional connectivity, that is, how strongly the activation correlated in the brain areas that participate in encoding and memory formation.
The exercise survey allowed subjects to be grouped on the basis of aerobic and non-aerobic exercise during the prior week. The aerobic group remembered more items on the episodic memory task. The aerobic group also revealed stronger functional connectivity among several areas in the memory network. Additionally, there was a correlation with levels of the inflammatory chemical: subjects showing strong functional connectivity had the lowest levels of interleukin-6.
Limitations of the study include a failure to distinguish the intensity of exercise. For example, one can jog three hours a week at high speed or rather leisurely. Also, actual fitness of each subject was not measured, just a log of their exercise activities during the prior week. Another factor is that only one inflammatory chemical was studied. Interleukin-6 is one of a large family of such chemicals known as cytokines, and there are other inflammatory chemicals as well. Moreover, the significance of interleukin was not evaluated. When brain is damaged (by stress, metabolic production of free radicals, or whatever), interleukin-6 is released as a defense mechanism.
Nonetheless, a strong correlation, consistent with prior studies, was demonstrated between aerobic exercise, inflammation, and mental function. The authors did not speculate on why these effects occurred. I will.
Two contributing factors are obvious. One obvious factor is that aerobic exercise improves cardiovascular function and likely improves blood flow through the brain. The other obvious factor is that aerobic exercise releases the "feel-good" endorphins. Endorphins alleviate stress. Stress, more specifically the cortisol released during stress, shrinks the synaptic connections between neurons, which of course can be expected to diminish functional connectivity and information processing efficiency. Stress increases the level of inflammatory chemicals like interleukin-6. The low level of interleukin-6 in the aerobic group indicates that these brains were somewhat protected from the ravages of stress and free radicals.
Bottom line: aerobic exercise is good for older people. In addition to the well-known cardiovascular benefits, aerobic exercise makes people more sharp mentally. How one gets the needed aerobic exercise probably doesn't matter, as long as the exercise is sufficiently intense and sustained. Jogging, bike riding, swimming, and fast-moving sports should all prove beneficial.
Readers of this column will be interested in "Memory Medic's" e-book, Improve Your Memory for a Healthy Brain. Memory Is the Canary in Your Brain's Coal Mine (available in all formats from Smashwords.com). The book, devoted exclusively to memory issues in seniors, includes review of many of the ideas in these columns over the last five years.
Sources:
Thielen, Jan-Willem et al. (2016. Aerobic activity in the healthy elderly is associated with larger plasticity in memory related brain structures and lower system inflammation. Frontiers in Aging Neuroscience. 26 December. doi.: 10.3389/fnagi.2016.00319
Erta, M., Quintana, A., and Hidalgo, J. (2012) Interleukin-6, a Major Cytokine in the Central Nervous System. Int. J. Biol. Sci. 8(9):1254-1266. doi:10.7150/ijbs.4679. Available from http://www.ijbs.com/v08p1254.htm
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