Preventing dementia: the crucial role of lifestyle habits

Non-communicable diseases (cardiovascular diseases, cancers, dementia, and diabetes) have the common characteristic of increasing exponentially from adulthood and accounting for the majority of deaths at older ages. This increase in the incidence with age is particularly striking with regard to dementia: while these neurodegenerative diseases are extremely rare before the age of 55 (and, in these cases, generally caused by defective genes transmitted by heredity), their incidence increases sharply in the years that follow. From the age of 65, for example, the risk of developing Alzheimer’s disease doubles every 5 years, reaching almost 50% after the age of 85. With the aging of the world’s population, the number of people suffering from dementia is therefore constantly increasing and could climb from 57 million in 2019 to 153 million by 2050.

Although this increase in the incidence of dementia has long been considered an inevitable consequence of the aging process, several studies conducted in recent decades have highlighted certain factors associated with individuals’ lifestyle that could reduce the risk of developing these neurodegenerative diseases. To take stock of this preventive potential, a group of experts led by the British medical journal Lancet has been conducting a periodic review of the evidence collected by studies on the influence of lifestyle on the risk of dementia since 2017, with the aim of proposing concrete prevention strategies that could reduce the burden of these diseases on individuals and society.

Mitigation of risk factors
The 14 modifiable risk factors identified to date and described in detail in the third report of the Lancet Commission on dementia prevention, published in 2024, are illustrated in Figure 1. All of these factors influence to varying degrees interdependent processes that are involved in the development and progression of dementia, namely vascular damage, neuronal damage (neuropathologies), stress and inflammation, and what is called “cognitive reserve.” This concept of cognitive reserve comes from studies of people who did not develop any apparent symptoms of dementia during their lifetime, but who were found at autopsy to have brain changes typical of advanced neurodegenerative diseases (e.g. Alzheimer’s disease). It is proposed that these people have developed neural circuits with great flexibility and adaptability during their lifetime that allow them to compensate for the loss of neurons affected by the damage characteristic of dementia.

Figure 1. Mechanisms potentially involved in reducing dementia risk through lifestyle modifications. Note that all modifiable factors have impacts on multiple brain processes involved in the development of dementia. Adapted from Livingston et al. (2024).

Cardiovascular risk factors
Interestingly, more than half (8 out of 14) of the risk factors for dementia that can be modified by lifestyle are also well-established risk factors for cardiovascular disease. In other words, adopting an optimal lifestyle for cardiovascular health also has several positive implications for dementia prevention. As mentioned earlier, this link is not so surprising, since the brain alone receives 15% of the cardiac output and uses about 20% of all the oxygen consumed by the body. Brain activities such as thinking, memory, or reasoning are therefore extremely dependent on the health of the heart and blood vessels. This is particularly true for vascular dementia, caused by pathologies affecting the blood vessels (e.g. stroke).

This link between cardiovascular and brain health is suggested by several studies: for example, one study showed that the presence of many cardiovascular risk factors in young individuals (18-30 years old) is already associated with a decline in several cognitive functions in middle age (reduced memory and executive functions). Conversely, adopting healthy lifestyle habits known to improve cardiovascular health, particularly not smoking, a healthy diet, and regular physical activity, is associated with an improvement in cognitive performance.

Some of these modifiable risk factors also have direct effects on the brain: regular physical activity, for example, is associated with changes in the structure of the brain itself, including an increase in the volume of the hippocampus, the brain structure involved in memory. Overall, it is estimated that addressing these eight modifiable risk factors could reduce the risk of dementia by about 20%.

Physical activity. A large number of studies have reported that regular physical activity is associated with a significant reduction in the risk of dementia. This protection is observed at all ages and probably involves better perfusion of brain tissue that reduces inflammation and promotes brain plasticity. Several molecules released during exercise (exerkines, see our article on this subject) could also exert neuroprotective effects and contribute to reducing the risk of dementia.

Obesity. Obesity in adulthood (40-65 years old) has been observed to be associated with an increased risk of dementia at older ages. Chronic inflammation associated with excess fat probably plays a role in this association, but given that obesity predominantly affects physically inactive people with many metabolic abnormalities (diabetes and hypertension, in particular), it is possible that these risk factors could also contribute to the increased risk. The currently available data tend to show that even relatively small body weight loss is associated with improved cognitive function and could therefore reverse, at least in part, the negative impact of excess weight on the risk of dementia.

Diabetes. Type 2 diabetes, which is a very common consequence of excess weight (especially obesity), is also associated with an increased risk of dementia, particularly if the disease develops in adulthood. The vascular complications of diabetes probably play a role in this increased risk (by increasing the risk of stroke, in particular), as do the insulin resistance and chronic inflammation typical of the disease, which are known to accelerate the formation of neurotoxic plaques.

Blood pressure. High blood pressure, particularly in people in their 50s, can damage the blood vessels of the brain, increasing the risk of vascular dementia and Alzheimer’s disease. However, studies suggest that this increased risk is reduced in people with hypertension who are treated with antihypertensive medications.

Cholesterol. Excess cholesterol in the brain can lead to the formation of aggregates of beta-amyloid and tau proteins, two types of deposits typically observed in the brains of patients with Alzheimer’s disease. Moreover, it has been observed that in adults, each increase of 1 mmol/L in LDL cholesterol is associated with an 8% increase in the incidence of dementia. An increased risk of dementia has also been observed in individuals who have high levels of LDL cholesterol (> 3 mmol/L).

Smoking. Studies show that smokers (but not ex-smokers) have a significantly higher risk (about 30%) of developing dementia than people who have never smoked.

Alcohol. As is the case for cardiovascular disease (see our article on this subject), the relationship between alcohol consumption and the risk of dementia seems very complex. On the one hand, high consumption of alcohol (>3 drinks per day) seems to be associated with an increased risk of dementia, but some studies report a decrease in this risk in light and moderate drinkers (1-2 drinks per day) compared to abstainers.

Air pollution. Fine particles (PM <2.5 µm) generated by the combustion of fossil fuels represent a well-established risk factor for cardiovascular disease and also seem to contribute to the development of dementia. For example, a meta-analysis of 20 studies conducted on 90 million people reported a 3% increase in the risk of dementia for each increase of 1 µg/m3 in PM2.5. Conversely, a reduction in exposure to PM2.5 was observed to be associated with a reduced risk of dementia.

Brain risk factors
The other modifiable risk factors identified by the Lancet Commission are actions that more specifically affect the brain, both from a physical point of view (prevention of head injuries, treatment of visual and hearing disorders) and from a cognitive point of view (education, social relationships, depression, intellectual work). In the latter case, it is proposed that sustained intellectual stimulation (long studies, intellectually demanding work, stimulating cognitive leisure activities) could contribute to the creation of the cognitive reserve mentioned earlier. Collectively, these modifiable risk factors could contribute to 25% of the reduction in lifestyle-related risk of dementia.

Education and intellectual work. Several studies have reported that higher levels of education are associated with a lower risk of dementia. It is postulated that intellectual activity during schooling helps to develop a cognitive reserve that can protect the brain against neuronal damage associated with aging. It seems that this association between education and dementia is also due to the fact that more educated people often have occupations that are more cognitively demanding than those with less education. This contribution of cognitive stimulation at work seems important, as one study showed that people who have little education but intellectually stimulating jobs have a similar reduction in dementia risk as those who are educated but whose jobs offer little cognitive stimulation.

Social relationships. Social isolation and loneliness have repeatedly been associated with an increased risk of several chronic diseases, both physically and psychologically (see our article on this subject). These two conditions are not identical: while social isolation is an objective parameter that is measured by the number and frequency of interpersonal contacts (marital status, social network, group activities), loneliness is a perception that rather involves dissatisfaction with the quality of the social relationships that a person maintains (frequency, intimacy). A person can therefore suffer from loneliness even when maintaining relationships with several people and, conversely, a socially isolated person may not feel lonely even if they live apart from others.

But whether it is loneliness or social isolation, studies show that these two forms of lack of interpersonal relationships are associated with an increased risk of dementia. Isolated and/or lonely people are deprived of interactions that help build cognitive reserve, adopt better lifestyle habits, and reduce stress and chronic inflammation.

Depression. Studies indicate that people who experience depressive episodes during their lifetime have a higher risk of developing dementia at later ages. However, this increased risk can be greatly reduced by psychotherapy, drug therapy (antidepressants), or a combination of both approaches. The mechanisms responsible for this association between depression and dementia remain poorly understood, but it is possible that an overproduction of cortisol can trigger an inflammatory response and cause damage to the brain, particularly in the hippocampus.

Head injuries. Several studies have observed an increased risk of dementia in people who have suffered blows to the head during their lifetime. This increase appears to be linked to the severity of the head injury, but is also observed for less intense but repeated traumas, such as those occurring in the context of certain contact sports (rugby, soccer, football). For example, one study showed that professional footballers had a 30% lower risk of premature mortality than the general population (due to the positive effect of exercise on health), but that their risk of being affected by dementia was considerably higher.

Hearing loss. A meta-analysis of several studies indicates that hearing loss is associated with an approximately 30-40% increased risk of dementia, but that this increased risk can be substantially reduced by the use of hearing aids. It is postulated that this link may involve certain psychosocial factors associated with hearing loss (loneliness, depression, social isolation) as well as a reduction in cognitive reserve caused by a decrease in neuronal stimulation. In any case, given that hearing loss affects a large number of people as they age (up to 20% of the world population), correction of hearing loss represents an important modifiable risk factor for dementia.

Visual impairment. In older people, a loss of visual acuity is associated with an approximately 30-40% increase in the risk of dementia. This increase is observed for cataracts and diabetic retinopathy, but not for glaucoma and age-related macular degeneration. Treating visual loss therefore appears to be an interesting approach to preventing dementia.

As with all chronic diseases, it is therefore possible to prevent a significant proportion of dementia through lifestyle changes. Addressing the risk factors identified by the Lancet Commission represents a concrete way to achieve this and to considerably reduce the devastating impact of these diseases on society.