Given the vast number of people in the United States who are
approaching 65 years of age, there is a need for interdisciplinary
research on factors influencing the trajectory of cognition and brain
aging in older adults. In a recent review published in Nutrients, researchers examine the collective effect of diet and exercise interventions on age-related cognition and brain health changes.
Study: Impact of Diet and Exercise Interventions on Cognition and Brain Health in Older Adults: A Narrative Review. Image Credit: Isarat / Shutterstock.com
Age-related cognitive decline
Reduced processing speed is one of the major cognitive deficits
observed in older adults, in addition to impaired semantic and episodic
memory. Likewise, working memory that actively maintains information in
the short term to enable goal-directed decision-making also declines
because of aging.
Reduced working memory results in a corresponding reduction in
executive functions in advanced age. Due to structural and functional
changes in the brain, aging also affects an individual's crystallized
and fluid intelligence.
Structural changes in the brain associated with aging include reduced
gray matter volume and cortical thickness. Gray matter volume, a
measure of neuronal and glial cell
bodies, declines in volume within multiple brain regions, including the
medial temporal lobe of the hippocampus and entorhinal cortex during
aging. Specifically, age-related reduction of hippocampal volume,
resulting from neuronal cell loss and a decrease in neurogenesis, is
associated with decreased cognitive performance on memory, spatial
learning, and emotional regulation tasks.
Effect of diet and exercise on aging
It is crucial to understand the relationship between nutrient
consumption and neuronal function, neurometabolic processes, and
cognitive decline.
There is growing evidence that nutrients from various foods across
multiple food groups have synergistic effects beyond the effects of
individual nutrients. For example, the absorption of vitamins from green
salad improves when served with olive oil and vinegar rather than a
fat-free ranch dressing.
To
date, the Mediterranean diet (MeDi), Dietary Approaches to Stop
Hypertension (DASH), and Mediterranean-DASH Intervention for
Neurodegenerative Delay (MIND) diets are most frequently referenced in
the literature. Each of these diets appears to improve neurological
signs of aging, including cell membrane and vascular integrity,
inflammation, resolution, and oxidation, as well as lipid and glucose
metabolism.
Considerable evidence suggests that the MeDi and MIND diets are
associated with both general and domain-specific facets of cognitive
ability. For example, several studies have associated the MeDi diet with
attention and long-term memory. Likewise, adherence to the MIND diet is
positively associated with visuospatial ability, perceptual speed, and
executive function.
The impact of the ketogenic diet (KD) and intermittent fasting (IF)
on cognition and brain function have also been widely studied, as weight
management diets appear to improve cognitive functioning. Likewise,
weight loss achieved through bariatric surgery enhances attention,
memory, and executive function.
In addition to diet, exercise positively affects cognition, as
demonstrated by a previous study in which overweight and obese adults
were enrolled in a one-year behavioral weight loss intervention. These
patients were on an energy-restricted diet, an energy-restricted diet
with 150 minutes of moderate-intensity exercise every week, or an
energy-restricted diet with 250 minutes of exercise every week.
Post-intervention, weight markedly decreased across both groups. More
specifically, the high-exercise group improved their performance on
Iowa Gambling Task (IGT) reward relative to the other two study groups.
Overall, more exercise with behavioral weight loss regimens had an
additional benefit on executive functioning, even with no weight loss
benefits.
Endurance exercise typically encompasses walking, jogging, running,
swimming, and cycling, with walking being the most practiced form among
older adults. Higher endurance fitness levels are associated with less
age-related brain volume decline.
Randomized controlled trials examining the role of endurance exercise
on cognition have led to mixed results. However, all evidence suggests
that endurance exercise in older adults improved cognitive performance,
visual attention, and memory, promoted brain plasticity, and weakened
hippocampal atrophy.
Similarly, a recent systematic review found that resistance training
positively affected older adults' executive and global cognitive
functions. This form of exercise also positively impacted memory, albeit
weakly, and did not significantly improve attention. Additionally,
tri-weekly, as compared to biweekly resistance training, positively
affected general cognitive abilities.
No evidence of an interference effect of aerobic and resistance
training has been reported. However, literature comparing resistance or
combined exercise to a non-exercise control is limited. Thus, it remains
unclear which exercises should be prescribed to maintain and enhance
cognition and brain health among older adults.
Behavioral interventions like yoga appear to mitigate age-related and
neurodegenerative decline. In one review examining the effects of
practicing yoga on brain structures, function, and cerebral blood flow,
yoga positively affected the structure and function of the hippocampus,
prefrontal and cingulate cortex, amygdala, and neuronal networks.
A recent literature review evaluating the effect of tai chi, a
traditional Chinese martial art, on brain structure and neurobehavior
changes found that this form of exercise also increased cortical grey
matter volume, improved neural activity and homogeneity, and increased
neural connectivity in the frontal, temporal, and occipital lobes,
cerebellum, and thalamus.
Conclusions
All diets evaluated in this review addressed factors associated with
aging and neurodegenerative diseases like Alzheimer's disease and
related dementias (ADRD). Depending on the type and intensity, exercises
were found to positively affect brain vascularization, neurotransmitter
regulation, growth factors, and neurogenesis.
Journal reference:
- Key, M. N., & Szabo-Reed, A. N. (2023). Impact of Diet and
Exercise Interventions on Cognition and Brain Health in Older Adults: A
Narrative Review. Nutrients 15(11);2495. doi:10.3390/nu15112495