The wider the brain's neuronal circuits, the lower the risk of dementia in old age.
“Dementia is by no means an inevitable consequence of reaching retirement age, or even of entering the ninth decade.” This is the main message of the Lancet Commission on “Dementia Prevention, Intervention, and Care,” which identified measures to reduce the risk of the disease.
Early prevention is crucial. Nearly 50 million people have the disease, but the number threatens to triplicate by 2050 if we don’t take preventive measures.
Prevention requires reducing risk factors during the whole course of life. Memory loss, language and speech difficulties, social isolation, mood changes, agitation, delusions; the most common symptoms of dementia start to appear in people older than sixty-five. Dementia, however, ought not to be confused with mild cognitive decline. The memory ability and the quickness of thought decay in about one-fifth of the people older than sixty-five, but everyday tasks can still be performed; they will just require a bigger effort or new strategies.
The main risk factor for dementia, age, obviously cannot be prevented or modified (the same goes, at least for now, for genetic factors linked to some forms of dementia). It might be possible, however, to push further the age at which dementia occurs today – i.e. beyond sixty-five years – by mitigating other risk factors for the disease.
The Lancet Commission has identified nine risk factors that significantly increase the possibility of dementia in old age. All these nine risk factors can be targeted and reduced, thus increasing the brain cognitive reserve.
Dementia prevention and cognitive reserve
The brain cognitive reserve is the brain’s capacity to make us remember, imagine and resonate things. A large cognitive reserve increases the brain’s ability to perceive reality and adequately react to it: it endows the brain with a more diverse array of neural circuits that can be modulated and coordinated to carry out everyday tasks and to respond to challenges. A brain with a large cognitive reserve is a resilient brain.
The brain cognitive reserve is modifiable because the brain is plastic: its cells (neurons) can form new connections (synapses) and establish new circuits that regulate our cognitive functions throughout life.
Cognitive reserve and the risk factors for dementia
By increasing our cognitive reserve, we reduce our risk of dementia in late life. Why? A resilient brain has more functional options: if one neural circuit gets damaged, it can activate alternative circuits that substitute the damaged one.
The Lancet Commission explains that it’s possible to increase the cognitive reserve by taking on behaviors that limit or reduce the nine risk factors stated above. These behaviors should become a lifestyle that should be adopted since childhood.
Possible preventive interventions
School education, study, and reading increase the cognitive reserve because they stimulate critical thinking and thus brain plasticity. It should be protracted beyond school years. Education also means teaching healthy habits, from healthy nutrition to regular physical activity.
Hypertension, obesity, diabetes must be controlled because they may cause direct (hypertension) or indirect (obesity and diabetes) vascular damage in the brain and thus compromise its function, with a reduction of the cognitive reserve.
Hearing loss since midlife is associated with increased risk for dementia. The reduced sound stimuli change the brain’s activity, thus making social interactions more difficult, which, in turn, might lead to isolation and depression. Hearing aids and initiatives that promote social interactions can help stabilize and improve the cognitive reserve.
Regular physical activity throughout life is associated with lower risk of dementia in old age. In addition, older people who regularly exercise have a higher probability to maintain normal cognitive abilities than people who are physically inactive.
The importance of physical exercise in dementia prevention
Aerobic exercise, which improves the cardiorespiratory function, and resistance training, which increases muscle force and resistance, are the most beneficial to cognitive capacities: the former especially to memory, the latter to reasoning capacities. Tai Chi, an exercise that combines slow movements with breathing, also improves attention and processing speed.
Any exercise program must be adapted to age, physical conditions, and health status to be beneficial and improve the cognitive reserve. But how does physical exercise reduce the risk of dementia?
Besides improving muscle tone and cardiovascular function, and reducing the risk of obesity and diabetes, regular physical activity increases the blood flow to the brain and promotes the release of chemicals that protect brain neurons and stimulate brain plasticity.
Physical exercise directly increases the cognitive reserve by remodeling the connections between neurons, and by improving the brain’s functional capacities. A study in healthy adults, aged between 55 and 80 years, has demonstrated that walking for 40 minutes three times a week for a year increased the size of the hippocampus (a brain structure implicated in memory) and improved memory.
There is, however, not enough evidence yet that physical exercise protects against diseases (Alzheimer’s disease, dementia with Lewy bodies etc.) that cause dementia. Studies to clarify this point are ongoing.
Livingston, Gill, et al. “Dementia prevention, intervention, and care.” The Lancet (2017).
Image source: Max Pixel