The Potential Mediation of the Effects of Physical Activity on Cognitive Function by the Gut Microbiome

Abstract

The population of older adults is growing dramatically worldwide. As older adults are at greater risk of developing disorders associated with cognitive dysfunction (i.e., dementia), healthcare costs are expected to double by 2040. Evidence suggests dementia may be slowed or prevented by lifestyle interventions, including physical activity (PA). PA is associated with improved cognitive function and may reduce risk for dementia by mitigating known risk factors (i.e., cardiovascular diseases) and/or by enhancing neurochemical processes. An emerging area of research suggests the gut microbiome may have similar neuroprotective effects. Altering the gut microbiome has been found to target physiological processes associated with dementia risk, and it influences gut-brain-microbiome axis signaling, impacting cognitive functioning. The gut microbiome can be altered by several means (i.e., disease, diet, prebiotics, probiotics), including PA. As PA and the gut microbiome independently influence cognitive function and PA changes the composition of the gut microbiome, cognitive improvement due to PA may be partially mediated by the gut microbiome. The present article provides an overview of the literature regarding the complex associations among PA, cognitive function, and the gut microbiome, as well as their underlying biological mechanisms. A comprehensive, theoretical model integrating evidence for the potential mediation is proposed.

Systematic Review of the Effects of Exercise and Physical Activity on the Gut Microbiome of Older Adults

“…PA/exercise might be a way to improve the gut microbiome during ageing since it influences several organs, cells, and tissues, and involves several molecular pathways. Previous studies have shown that PA/exercise have several benefits during the ageing process such as improvements in cognitive function [ 55 , 56 ], promotion of cardiovascular health [ 57 ] and improvements in the musculoskeletal system [ 58 , 59 , 60 ], making it a precious tool to counteract the age-associated changes that occur in those systems. Besides the benefits mentioned previously, recent studies [ 61 , 62 , 63 , 64 ] on the effects of exercise on the gut microbiome of older people have suggested that exercise might beneficially affect its composition and even reverse some age-associated taxonomical changes, ultimately leading towards healthy ageing.…”

Can physical exercise help people with irritable bowel syndrome? How substantial is the evidence?

“…Physical exercise is classified according to the type and intensity into dynamic and static, and based on muscle metabolism, into aerobic and anaerobic [36,37]. Most static exercises, such as muscle building, weightlifting, Tai Chi, and Yoga and Benson relaxation, are performed anaerobically, while dynamic exercises lasting for more than several minutes require increased heart and breathing rates to maintain exercise sessions, and could be low-tomoderate, such as walking, jogging, and cycling, and vigorous exercise, like football, treadmill running and swimming [37][38][39].…”

“…Furthermore, metabolic equivalent units (METs) are often used to classify aerobic physical exercise as light-to-mild, moderate, or vigorous, where METs refer to the amount of oxygen consumed during exercise compared to the rest status, and 1 MET typically equals 3.5 ml O 2 /kg body weight/ minute [36]. Accordingly, the low-to-mild, moderate, and vigorous exercises equal (1.6-2.9 METs), (3-6 METs), and (> 6 METs), respectively [38].…”

“…In contrast to vigorous exercise, light-moderate exercise can increase the secretion of secretory immune globulin A, which plays a significant role in boosting the immune system and providing protection against different pathogens [57,58]. Increasing physical activity is also associated with enhanced intestinal immune function due to increased microbial diversity resulting in increased short chain fatty acids (SCFA), which can modulate energy balance, increase nutrient availability, and promote intestinal barrier maintenance and homeostasis [12,38,59,60].…”

“…Exercise can improve brain health by regulating neurogenesis and neuroplasticity by affecting BDNF and serotonin production, reducing inflammatory markers, and improving BGA signaling [28,38,96]. During moderate aerobic exercise, brain functions are modulated, and areas such as the frontal lobe and the parietal cortex are activated, which, in turn, results in escaping excessive nervous activity, regulating brain balance, and thus effectively relieving the pain [16,47,[51][52][53].…”