14 modifiable risk factors for dementia, according to the Lancet Commission

When we talk about dementia or Alzheimer's, we often think of it as something inevitable, as if everything depended on age or genetics. But science has been saying for years that a significant part of the risk of dementia can indeed be reduced.

The Lancet Commission, one of the leading international groups in dementia prevention, intervention, and care, published an update to its report in 2024. In it, it identifies 14 modifiable risk factors that, when addressed throughout life, could prevent or delay up to approximately 45% of dementia cases worldwide.

You can see the Lancet Commission report here.

What are the modifiable risk factors for dementia or Alzheimer's?

A risk factor is something that increases the likelihood of developing a disease. In this case, we are talking about factors associated with an increased risk of dementia. The important part lies in the word "modifiable." These are factors we can, at least in part, act upon.

Even so, they are not guarantees. Neither having one of these factors means a person will develop dementia, nor does not having them ensure absolute protection. But when we look at the population as a whole, these factors carry significant weight.

The Lancet Commission uses a measure called the Population Attributable Fraction (PAF). This measure estimates what percentage of cases could be avoided if a risk factor were completely removed from the population. To calculate it, it looks not only at how much a factor increases risk, but also at how many people are exposed to it. That is why a relatively common factor can have a lot of weight. If it affects millions of people, its population impact can be enormous, even if the individual risk is not that great.

How the Lancet Commission identified these 14 factors

The Lancet Commission did not conduct a single new study tracking people from scratch. What it did was more like a large audit of the available scientific evidence.

First, it identified potentially modifiable risk factors already present in clinical guidelines and scientific literature. Then it reviewed meta-analyses, which are studies that group the results of many investigations to obtain a more robust estimate. From there, it calculated the relative risk of each factor—that is, how much the risk of dementia increases in a person exposed to the factor compared to one who is not.

It then combined that risk with the prevalence of the factor in the population. Prevalence means how many people have that factor. This provides an estimate of how much dementia could be reduced if that factor were eliminated.

In addition, the Commission applied an important statistical adjustment: the factors overlap. The same person can have obesity, hypertension, and diabetes at the same time. If we added all the percentages without correcting for that overlap, we would be counting part of the same risk multiple times.

The model has grown over time. In 2017, 9 factors were identified; in 2020, they increased to 12; and in 2024, they reached 14. This latest 2024 update notes that these 14 factors could explain about 45% of potentially preventable or delayable dementia cases. Still, it is important to remember that most of this evidence comes from observational studies, which find associations between risk factors and dementia, but do not always prove direct causality.

Risk factors in childhood and youth

Dementia prevention does not start at age 70. One of the most interesting points of the Lancet model is that it organizes risk factors according to the stage of life in which they seem to have the most impact.

Low level of education (7% potential reduction)

The low level of education is the only factor situated in the first stage of life. The Commission links it to what is called cognitive reserve.

Cognitive reserve is, simply put, the brain's ability to compensate for damage. A brain that has learned, read, solved problems, developed skills, and used different mental strategies throughout life may have more resources to continue functioning when the changes typical of aging or a disease begin to appear. According to the report, having received few years of formal education is associated with an approximately 60% higher risk of developing dementia. Globally, improving access to education could theoretically prevent or delay about 5% of cases.

This does not mean that only formal education provides protection. Going to school matters, of course, but continuous learning, reading, conversation, curiosity, mental challenges, and staying intellectually active also count.

How does education influence brain health?

• It helps build cognitive reserve: Education contributes to developing cognitive reserve, that is, the brain's ability to continue functioning despite the appearance of changes or lesions with aging.
• It promotes more efficient brain networks: Learning to read, write, calculate, solve problems, and relate ideas forces the brain to create and strengthen connections between neurons. Sustained cognitive stimulation promotes synaptogenesis, which is the formation of new connections between neurons, and helps brain networks work in a more flexible and efficient way. It is not just about accumulating knowledge. The benefit also lies in the effort of learning, understanding, practicing, and seeking solutions.
• It can influence opportunities throughout life: The level of education is also related to other aspects that affect health. People who had fewer opportunities to study may have held more precarious or less stimulating jobs, faced greater financial difficulties, and encountered more barriers to accessing good nutrition, healthy housing, or adequate medical care. Therefore, part of the relationship between education and dementia does not come solely from what was learned in school. It also reflects the social, occupational, and health conditions that accumulate over decades.

It is important to emphasize that the level of education alone does not measure intelligence, curiosity, or the ability to learn. Many people could not continue their studies because they had to start working, take care of their family, or live in a time when access to education was much more limited, especially for women.

These circumstances also help explain some differences observed between countries, generations, and sexes. For example, in certain studies, part of the higher risk of dementia attributed to women disappears when comparing men and women with similar educational opportunities.

This cognitive reserve can (and should) continue to be built throughout life, not just in childhood and youth! The education received during childhood is important, but the brain retains its ability to learn and adapt throughout life. Studies have observed that people with a low level of education but mentally demanding jobs have a lower risk of dementia than those who also perform tasks that are not very stimulating.

Risk factors in midlife

Between the ages of 45 and 65, there is a key stage for prevention. It is an age when many people still feel far from old age, but the body begins to show signs: slightly higher blood pressure, cholesterol, less movement, more stress, worse sleep, or extra weight. And that is precisely where there is room for action.

Untreated hearing loss (7% potential reduction)

Untreated hearing loss is one of the factors with the most weight in the Lancet model. It is estimated that preventing or properly treating it could theoretically prevent or delay up to 7% of dementia cases worldwide. Although it is usually classified as a midlife risk factor, its effects can accumulate over years and continue into more advanced ages.

How does hearing loss affect the brain?

• The risk increases as hearing worsens: People with hearing loss have a higher risk of dementia than those who maintain normal hearing. Furthermore, the risk increases progressively as hearing capacity decreases. For every additional 10-decibel loss, the risk of dementia can increase between 4% and 24%.
• The brain has to work harder to listen: When hearing worsens, the brain must dedicate many more resources to interpreting incomplete or unclear sounds. Instead of using its full capacity to comprehend, remember, or relate ideas, a significant part of mental effort is spent simply deciphering what has been said. Over time, this additional load can affect memory and information processing.
• It receives less stimulation: Listening to conversations, music, ambient sounds, and familiar voices keeps the brain connected and active. When hearing loss reduces these stimuli, opportunities to exercise attention, language, and memory also diminish. This can weaken cognitive reserve—the brain's ability to compensate for changes and damage associated with aging.
• It can promote social isolation: When it is difficult to follow a conversation, it is easy to start avoiding calls or group plans. Sometimes a person gets tired of asking for things to be repeated or fears responding incorrectly.

To avoid hearing loss, the first step is not to normalize hearing worse and worse. Losing hearing should not be automatically accepted as something inevitable and unsolvable. Some signs that should be checked include needing to turn up the volume significantly, frequently asking for phrases to be repeated, confusing similar-sounding words, or feeling that others speak too softly or enunciate poorly.

Given these signs, it is recommended to request a hearing assessment. Even if the loss is mild, it is best to have check-ups, as hearing impairments often progress gradually, meaning the individual may take time to notice.

When indicated, using hearing aids is key. Studies show that people with hearing loss who use hearing aids have a lower risk of cognitive decline and dementia than those who do not. In people at high risk, their use has also been linked to a significant reduction in the rate of cognitive decline. In addition, hearing better facilitates communication, promotes social participation, and allows for clearer follow-up on medical instructions.

However, it is important that they are correctly fitted. A hearing aid kept in a drawer does not protect the brain.

Another important aspect we must take care of is protecting our ears from harmful noise. Prolonged exposure to loud sounds can irreversibly damage the cells of the inner ear. To reduce this risk, use hearing protection in jobs or activities with high noise, lower the volume on headphones, avoid listening to music at maximum power, take breaks after prolonged exposure, and stay away from loudspeakers and very intense sound sources.

High LDL cholesterol (7% potential reduction)

LDL cholesterol, which we usually know as “bad cholesterol,” has been one of the new risk factors included in the 2024 Lancet Commission report.

According to the report's estimates, keeping it under control could theoretically prevent or delay up to 7% of dementia cases worldwide.

Studies show that the higher the LDL cholesterol during midlife, the greater the risk of developing dementia years later. For every 1 millimol per liter increase, the risk of dementia increases by approximately 8%. Furthermore, having LDL cholesterol values above 116 milligrams per deciliter has been linked to a 33% increase in dementia risk.

These figures should not be interpreted in isolation, because the appropriate level also depends on age, family history, and the presence of other health problems. Therefore, the important thing is to evaluate the result with a healthcare professional.

How does high cholesterol affect the brain?

• It can damage the brain's blood vessels: when there is too much LDL cholesterol in the blood, it can accumulate on the walls of the arteries and promote the formation of plaques. Over time, the arteries become narrower and stiffer, which hinders the delivery of blood and oxygen to the brain. It also increases the risk of suffering a stroke, that is, an interruption of cerebral blood flow.
• It can promote changes related to Alzheimer's: cholesterol also seems to be related to the accumulation of beta-amyloid and tau, two proteins involved in Alzheimer's disease. Beta-amyloid can form deposits between neurons, while tau protein can accumulate inside them and hinder their function. Excess cholesterol could favor these processes, although the relationship is complex and is still being studied.
• HDL cholesterol helps remove the excess: HDL cholesterol, known as “good” cholesterol, participates in transporting excess cholesterol from tissues to the liver, where it can be eliminated. Therefore, it is not enough to look only at total cholesterol. It is advisable to know LDL, HDL, and triglyceride levels to obtain a more complete view of cardiovascular risk.

To control cholesterol, the first step is to check it through blood work. High cholesterol usually does not cause symptoms. A person can feel perfectly fine and maintain high levels for years without knowing it. The only way to detect it is through a blood test. The frequency of check-ups will depend on age, family history, weight, blood pressure, and other risk factors.

Some tips for taking care of cholesterol:

• Maintain a consistent healthy diet: Diet can help reduce LDL cholesterol and, above all, improve cardiovascular health as a whole. It is advisable to prioritize vegetables, fruits and legumes, whole grains, raw nuts, fish, and olive oil. It is also recommended to limit sausages and processed meats, pastries and ultra-processed products, sugary drinks, and foods rich in saturated and trans fats.
• Stay physically active: Regular exercise helps improve the cholesterol profile, control weight, reduce blood pressure, and protect blood vessels.
• Avoid tobacco: Smoking damages artery walls, promotes cholesterol accumulation, and reduces HDL cholesterol levels. Quitting smoking is one of the most important decisions for taking care of circulation, the heart, and the brain.
• Also monitor blood pressure, sugar, and weight: High cholesterol often coincides with other factors such as hypertension, diabetes, or excess weight. These problems do not act independently. When they appear together, the damage to blood vessels can be greater.

If cholesterol remains high and lifestyle changes are not enough, a healthcare professional may recommend medication to lower cholesterol.

Depression (3% potential reduction)

Depression does not only affect mood. When it appears in midlife, it is also associated with a higher risk of developing dementia years later. In an analysis that brought together several studies with follow-ups of between 10 and 14 years, people with depression showed more than double the risk of dementia.

This relationship can persist for a long time. A large study conducted in Denmark found that the risk remained higher even 20 to 39 years after the depression diagnosis. This association has also been observed when depression appears in early adulthood, during midlife, or at later stages.

In old age, the relationship can work in two directions.

On one hand, sustained depression has been associated with inflammation, changes in the hippocampus (a key region for memory), as well as sleep, less physical activity, and more isolation. On the other hand, in some people, depressive symptoms may appear as an early sign of a neurodegenerative process that has not yet been diagnosed.

That is why depression with recent onset in old age warrants a complete medical evaluation, especially if there are also changes in memory, language, orientation, or behavior.

How does depression affect the brain?

• Sustained stress can affect the hippocampus: Depression can alter the body's stress response and keep levels of cortisol—a hormone that helps us respond to demanding situations—elevated for too long. When this activation is prolonged, it can affect the hippocampus, an area of the brain essential for learning and forming new memories. Some studies have linked sustained depression to a reduction in its volume and inflammatory processes that can damage neurons.
• It can hinder self-care: Depression usually reduces energy, initiative, and motivation. Simple activities like going for a walk, cooking, attending a medical appointment, or calling a friend can become an enormous effort. As a consequence, the person may exercise less, eat poorly, sleep irregularly, or socially isolate themselves. All these factors can also influence brain health.

That is why it is very important to ask for help when symptoms persist. It is advisable to consult a doctor when symptoms such as the following appear for at least two weeks:

• Sadness or a feeling of emptiness most of the day
• Loss of interest in activities that were previously enjoyable
• Constant tiredness or lack of energy
• Significant changes in sleep or appetite
• Difficulty concentrating or making decisions
• Intense feelings of guilt, worthlessness, or hopelessness
• A tendency to isolate oneself from other people

Traumatic brain injury (3% potential reduction)

A traumatic brain injury is a blow to the head that affects the brain. It can be severe, but it can also be mild and repeated, as occurs in some falls, accidents, or contact sports.

Blows to the head can trigger inflammation, neuronal damage, and processes that, over time, have been linked to a higher risk of cognitive decline.

Prevention here is very practical: wearing a helmet when appropriate, adapting the home to avoid falls, checking your vision, taking care of your balance, working on leg strength, and not minimizing blows to the head, especially in older people.

Physical inactivity (2% potential reduction)

Spending too much time without moving not only affects the muscles or the heart. It can also directly harm brain health and increase the risk of developing dementia.

According to the 2024 report, people who maintain a physically active life have approximately a 20% lower risk of developing any type of dementia and a 14% lower risk of suffering from Alzheimer's. Furthermore, this benefit is observed in people of different ages; it is never too early or too late to start moving more.

Why does exercise protect the brain?

• Improves blood flow to the brain: When we exercise, the heart and blood vessels work better. This helps the brain receive enough blood, oxygen, and nutrients. It also helps control blood pressure and stimulates the production of nitric oxide, a substance that helps blood vessels relax and dilate.
• Helps preserve brain volume: With age, it is normal for the brain to lose some volume. However, this reduction seems to be greater among people who perform little physical activity.
• Promotes brain plasticity and reduces inflammation: Brain plasticity is the brain's ability to adapt, learn, and create new connections between neurons. Exercise stimulates this capacity while simultaneously helping to reduce neuroinflammation—that is, sustained inflammation within the nervous system that can damage brain cells.
• Strengthens cognitive reserve: Cognitive reserve is the brain's ability to withstand certain damage before obvious problems with memory, reasoning, or attention appear. People who maintain good physical fitness usually have more resources to compensate for longer for the brain changes associated with aging and dementia.
• Activates substances that protect neurons: When we move, the body releases substances that favor the survival, growth, and communication of neurons. One of these is brain-derived neurotrophic factor, a protein that helps keep neurons healthy and facilitates the formation of new connections. Physical inactivity reduces the presence of these natural stimuli that help protect the brain.

Diabetes (2% potential reduction)

According to the 2024 Lancet Commission report, people with diabetes have approximately a 70% higher risk of dementia than those without this disease. The risk seems to be higher when diabetes starts before the age of 65 or 70, has been present for a long time, or glucose remains poorly controlled. In contrast, when it appears for the first time at very advanced ages, the relationship with dementia is not as clear.

How does diabetes affect the brain?

• It can damage cerebral blood vessels: Excess glucose maintained for years can damage both small blood vessels and larger arteries. In the brain, this damage can hinder the arrival of blood and oxygen, promote the appearance of small vascular lesions, and increase the risk of suffering a stroke. These alterations can progressively affect memory, attention, and the speed at which we process information.
• It can alter the use of energy in the brain: Insulin is the hormone that allows glucose to enter cells and be used as an energy source. In type 2 diabetes, insulin resistance appears; cells respond worse to this hormone, and the body needs to produce more to keep glucose under control. This resistance does not only affect the muscles or the liver. It can also alter insulin signaling in the brain and make it difficult for neurons to use energy properly.

Smoking (2% potential reduction)

The 2024 Lancet Commission now places smoking among the most important risk factors in midlife. Evidence indicates that smoking during this stage can be especially harmful, because the damage accumulates over decades. According to an analysis that brought together 37 studies, smoking in midlife is associated with approximately a 30% higher risk of dementia. But quitting tobacco can considerably reduce that risk. It is never too late to quit, although the sooner it is done, the greater the benefit.

How does tobacco affect the brain?

• Damages cerebral blood vessels: Substances present in tobacco smoke damage the walls of the arteries, favor their hardening, and facilitate the formation of plaques and clots. As a consequence, less blood and oxygen may reach the brain. It also increases the risk of suffering a stroke and accumulating small vascular lesions that, although they do not always produce immediate symptoms, can progressively affect memory, attention, and reasoning capacity.
• Promotes inflammation and oxidative stress: Smoking causes inflammation and increases oxidative stress, a process in which unstable molecules accumulate that are capable of damaging cells. Neurons are especially sensitive to this type of damage. When exposure is maintained for years, it can contribute to the premature aging of blood vessels and brain tissue.
• The risk may be higher the earlier you start: Starting to smoke in early adulthood means accumulating more years of exposure to tobacco. Studies show that people who smoke before age 50 may have a considerably higher risk of dementia than those who do not smoke. It is not only about how many cigarettes are consumed per day, but also the total number of years the habit is maintained.
• It can worsen other risk factors: Smoking often acts in conjunction with other problems such as hypertension, high cholesterol, diabetes, or cardiovascular disease. When several of these factors coincide, the damage to blood vessels can be greater. For this reason, quitting smoking also facilitates the control of other risks related to brain health.

Upon quitting smoking, the risk begins to decrease. Long-term follow-up studies even indicate that ex-smokers can end up having a risk similar to that of people who have never smoked, especially when they quit tobacco before age 65. This does not mean that all damage disappears immediately, but the body begins to recover from the moment you stop smoking.

Arterial hypertension (2% potential reduction)

Arterial hypertension is high blood pressure inside the arteries. Having high blood pressure in a sustained manner not only increases the risk of heart attack or stroke. It can also slowly damage the brain's blood vessels and promote the appearance of memory problems and other cognitive abilities over the years.

How does hypertension affect the brain?

• It can damage small blood vessels: When blood circulates with too much pressure, artery walls withstand constant strain. Over time, they can become stiffer, narrower, or injured. In the brain, this damage can hinder the arrival of blood, oxygen, and nutrients to neurons. It can also cause small cerebral infarcts that do not always cause visible symptoms but accumulate over the years. These lesions can weaken cognitive reserve.
• Damage accumulates over years: Blood pressure usually increases progressively throughout life. For this reason, keeping it elevated from the age of 40 or 50 can expose the brain to several decades of vascular damage.

  Interestingly, blood pressure may begin to decrease a few years before dementia becomes evident. This does not mean that previous hypertension has ceased to matter. On the contrary, the risk may stem from all the years that blood pressure remained high during midlife.

Furthermore, untreated hypertension poses a greater risk. People with hypertension who do not receive treatment have approximately a 42% higher risk of developing dementia than those without high blood pressure. In contrast, when hypertension is properly treated and controlled, this excess risk can be reduced to approach that of people without hypertension.

What can we do to control blood pressure?

• Measure it even if there are no symptoms: Hypertension usually progresses without giving clear signs, so a person can have high blood pressure for years without knowing it. The only way to detect it is to measure it periodically, especially starting at age 40 or earlier if there is a family history, diabetes, high cholesterol, overweight, or cardiovascular disease.
• Measure it correctly at home: To obtain a reliable result, rest sitting down for about five minutes before measuring it and avoid smoking, drinking coffee, or exercising during the half hour prior. Support your back and keep your feet on the floor without crossing your legs, place your arm supported at heart level, and perform two measurements separated by one or two minutes. It is also useful to write down the results to show the healthcare professional.
• Try to keep systolic pressure at 130 or less: Systolic pressure is the top number that appears when measuring blood pressure. It indicates the pressure exerted by blood when the heart contracts. The Lancet Commission recommends preventing or reducing hypertension and trying to keep this figure at 130 millimeters of mercury or less from the age of 40.
• Consult if side effects appear: Some people abandon treatment because they feel dizzy, tired, bloated, or have other discomforts. However, there are different types of medications, and it is often possible to adjust the dose or choose another alternative.
• Reduce salt in the diet: Excess sodium promotes fluid retention and can raise blood pressure. A large part of the salt we consume does not come from the salt shaker, but from prepared foods such as cold cuts, aged cheeses, instant soups, sauces, snacks, and ultra-processed products. Cooking more at home, reading labels, and using herbs or spices for flavor can help reduce it without making food taste bland.
• Stay in motion: Regular exercise helps the heart pump blood with less effort and helps arteries retain their elasticity.
• Take care of weight, sleep, and alcohol: Excess weight, poor sleep, and consuming too much alcohol can hinder blood pressure control. It is also advisable to assess the possibility of sleep apnea when there is heavy snoring, breathing pauses during the night, or a lot of fatigue during the day, as this disorder can contribute to keeping blood pressure elevated.

Obesity (2% potential reduction)

According to the studies in the Lancet Commission report, people with obesity in midlife have approximately a 31% higher risk of dementia than those who maintain a healthy weight.

How does obesity affect the brain?

• Fat accumulated in the abdomen is of special importance: So-called central obesity is excess fat around the abdomen. It can be assessed by measuring the waist or comparing the waist circumference with the hip circumference. This type of accumulation has been linked to approximately a 10% higher risk of dementia and cognitive decline. The association seems to be even more important in people over 65 years of age. Abdominal fat is especially active from a metabolic point of view. It can release substances that promote inflammation and make it difficult for the body to correctly use insulin, the hormone responsible for regulating blood sugar.
• It usually coincides with other risk factors: Obesity frequently appears along with hypertension, diabetes, high cholesterol, and a lack of physical activity. These problems can damage blood vessels and reduce the arrival of blood and oxygen to the brain. When several occur at the same time, their effects can accumulate. However, obesity does not seem to increase risk only because it is accompanied by these diseases. Studies show that the relationship with dementia remains even after taking blood pressure, diabetes, and other factors into account.
• It can promote sustained inflammation: Adipose tissue is not simply a place where the body stores energy; it also produces hormones and other substances involved in inflammation. When there is a significant excess of body fat, low-grade inflammation can appear that lasts for a long time. This inflammatory state can affect blood vessels, metabolism, and, possibly, the health of neurons.
• Stigma also harms health: People with obesity may suffer comments, discrimination, or disrespectful treatment, even within the healthcare setting. This stigma can generate sustained stress and increase levels of cortisol, a hormone the body releases to respond to difficult situations. When it remains elevated for too long, it can promote inflammation and harm physical and emotional health.

In weight management, it is not necessary to make drastic changes to see benefits. Even moderate and progressive weight loss, maintained over time, can be associated with improvements in metabolic health and some cognitive functions. The most important thing is to avoid quick fixes or overly restrictive measures, as they are usually difficult to sustain and can negatively affect muscle mass, especially with age.

The best results are achieved by combining a balanced diet with regular physical activity, including aerobic exercise, strength training, and more daily movement. It is also useful to prioritize fresh foods and reduce ultra-processed ones, as well as to monitor not only your weight but also your waist circumference and other health indicators. In older adults, any unintentional weight loss should be investigated, as it may have various causes. The goal is not to reach a specific number on the scale, but to improve overall health and maintain independence for as long as possible.

Excessive alcohol consumption(1% potential reduction)

Drinking too much alcohol during middle age can also increase the risk of developing dementia years later. The Lancet Commission considers excessive consumption to be more than 168 grams of pure alcohol per week. To give you an idea, this amount is roughly equivalent to more than 12 glasses of wine or more than 12 beers, although the exact amount depends on the size and alcohol content of each drink.

How does alcohol affect the brain?

• It can reduce brain volume: High and sustained alcohol consumption can directly damage the brain. Neuroimaging studies (tests such as MRIs that allow us to observe its structure) show that it is associated with a reduction in gray matter volume. Gray matter contains most of the neurons' cell bodies and is involved in functions such as memory, language, attention, and decision-making.
• Blackouts are a specific sign of risk: Drinking until you lose consciousness is not a trivial consequence. Studies have observed that experiencing episodes of alcohol-related blackouts can double the risk of dementia.
• It may accelerate the onset of Alzheimer's: Some genetic studies suggest that alcohol consumption is not only linked to a higher risk, but could also contribute to the earlier onset of Alzheimer's disease.

It is worth noting that alcohol-related brain damage can be reversible. Studies show that people with high consumption who manage to reduce it have a lower risk of dementia than those who continue to drink large quantities.

Risk factors in old age

In old age, the goal is not to resign yourself. It is to keep the brain as stimulated, protected, and accompanied as possible.

Many of these factors have to do with something we repeat often at Mr. Loris: independence is not preserved by chance. It is built through small decisions.

Social isolation(5% potential reduction)

According to the Lancet Commission, reducing social isolation could theoretically prevent or delay about 5% of dementia cases worldwide. People who maintain little contact with others have approximately a 60% higher risk of developing dementia than those who maintain an active social life.

Social isolation is an objective situation; it refers to having few contacts or participating little in activities with other people. Isolation and loneliness are related, but they do not mean exactly the same thing. A person can live alone and not feel lonely because they maintain a satisfying network of relationships. The opposite can also happen: being surrounded by people and feeling that you have no one to really talk to. Loneliness is the feeling that the social contact we have is not sufficient or does not have the quality we need. It has also been linked to a higher risk of dementia, even when the person is not objectively isolated.

How does isolation affect the brain?

• Reduces daily mental stimulation: Conversing, listening, telling a story, remembering names, interpreting gestures, or following the thread of a discussion are activities that keep the brain active. Social relationships engage memory, language, attention, and the ability to adapt to different situations. When this type of stimulation decreases for a long time, opportunities to exercise these functions also decrease. Social contact helps to strengthen cognitive reserve.
• May promote stress and inflammation: Feeling disconnected from others can keep the body's stress response activated. When this situation is prolonged, cortisol levels can increase, promoting inflammatory processes that affect blood vessels and brain health. Supportive relationships, on the other hand, can help reduce stress and make it easier for a person to feel accompanied when facing daily problems.
• May influence health habits: Having frequent contact with other people also encourages some protective behaviors. A friend can encourage us to go for a walk, a group activity can help us maintain a routine, and a family member can detect that we are eating poorly, forgetting medication, or skipping check-ups. When a person is very isolated, these changes can go unnoticed for longer.
• Is linked to physical changes in the brain: Studies have observed that people with greater social isolation may have lower gray matter volume in some frontal and temporal regions of the brain. Gray matter contains most of the neurons' cell bodies and is involved in functions like memory, language, planning, and decision-making. This does not prove that isolation is the only cause of these changes, but it reinforces the idea that social relationships are part of healthy brain aging.

The relationship between isolation and dementia can work both ways; sometimes it can be an early sign. Maintaining little social contact over years can increase the risk of cognitive impairment. However, a person starting to develop dementia may also gradually abandon activities and relationships before memory problems become evident. They may stop going out because they find it difficult to follow conversations, they feel disoriented, lose confidence, or feel embarrassed about forgetting names and words.

Therefore, if an older person who has always been sociable begins to isolate themselves suddenly or progressively, it is worth trying to understand what is happening. There may be hearing, vision, or mobility problems, depression, or cognitive changes that need evaluation.

Air pollution(3% potential reduction)

Air pollution was added to the Lancet Commission's model in 2020. According to their estimates, reducing it could theoretically prevent or delay about 3% of dementia cases worldwide.

How does pollution affect the brain?

• Smaller particles can enter the body: One of the pollutants of most concern is fine particulate matter, known as PM2.5. This name refers to particles that measure 2.5 micrometers or less. They are so small that they can penetrate deep into the lungs and enter the bloodstream. From there, they can promote inflammatory processes, damage blood vessels, and indirectly affect brain health. Studies show that for every small increase of 1 microgram per cubic meter in the concentration of these particles, the risk of dementia increases by about 3%.
• Black carbon seems to be particularly harmful: Within fine particulate matter, there are different components. One of them is black carbon, which is mainly generated by the incomplete combustion of fuels. It is found, for example, in diesel vehicle exhaust, wood stoves, coal, and some industrial processes. This pollutant is one of those that shows the clearest association with dementia. Continued exposure can contribute to vascular damage, inflammation, and oxidative stress, a process that damages cells.
• It may be more harmful if cardiovascular problems already exist: Air pollution primarily causes damage through inflammation and its effects on blood vessels. Therefore, its impact can be greater in people who already have hypertension, heart disease, atrial fibrillation, heart failure, or a history of stroke. In these cases, pollution adds to a cardiovascular system that is already more vulnerable and can accelerate brain damage.

Although we cannot always choose the air we breathe, it is possible to reduce some of our daily exposure. Many weather apps and official websites show a daily air quality index. On days with high pollution, it is advisable to adapt your activities and avoid times or places with higher concentrations of particles.

It is also advisable, as far as possible, to choose routes away from traffic. When walking, exercising, or traveling, it can help to choose side streets, parks, or paths separated from roads with heavy traffic. Pollutant concentrations are usually higher next to roads with heavy traffic. Moving just a few meters away from the source of emission can reduce the amount of particles inhaled.

Ventilating your home helps renew the indoor air, but it is best to do so when outdoor pollution is lower. If you live in an area with heavy traffic, it can be useful to open windows outside of rush hours and do so on the side of the home furthest from the road.

On the other hand, scented candles, incense, and air fresheners that produce smoke can worsen indoor air quality when used frequently. There is no need to be alarmed by lighting a candle from time to time, but it is worth avoiding the accumulation of multiple combustion sources in small or poorly ventilated rooms. A high-efficiency air purifier can help reduce fine particles in closed spaces, especially in homes located near busy roads, during smoke episodes, or when proper ventilation is not possible.

Untreated vision loss(2% potential reduction)

Untreated vision loss is the other new factor added in the 2024 update. According to the report's estimates, detecting and treating vision problems could theoretically prevent or delay about 2% of dementia cases worldwide. People with vision loss have approximately a 50% higher risk of developing dementia than those with good visual capacity.

How does vision loss affect the brain?

• The risk increases with the severity of vision loss: As with hearing, the more severe the difficulty in seeing, the greater the risk of cognitive impairment and dementia. This pattern is known as a dose-response relationship. In this case, it means that mild vision loss is associated with less risk than more severe loss.
• The brain receives fewer stimuli: Vision is involved in many activities (reading, recognizing faces, navigating, cooking, watching television...), and when vision deteriorates, these opportunities to stimulate attention, memory, language, and orientation decrease. This reduction in stimuli can weaken cognitive reserve.
• Can reduce activity and independence: Seeing worse can also make a person afraid of falling, stop driving, go out less, or give up activities they previously enjoyed. As a result, physical exercise, social contact, and intellectual stimulation may decrease. All of these are important factors for maintaining brain health.
• Some diseases can affect both the eyes and the brain: The retina is the layer at the back of the eye that transforms light into nerve signals so the brain can interpret what we see. The retina and the brain share characteristics and depend on good blood circulation. For this reason, some diseases can damage both tissues. One example is diabetes. When it persists for years, it can damage the small blood vessels in the retina and cause diabetic retinopathy. At the same time, it can also damage the brain's vessels and increase the risk of cognitive impairment.

Not all vision problems are linked to dementia in the same way.

• Cataracts: Cataracts appear when the lens of the eye loses transparency. This makes vision blurry, colors appear duller, or makes it difficult to see in low light. Studies in the Lancet report found an association between cataracts and a higher long-term risk of dementia.
• Diabetic retinopathy: Diabetic retinopathy occurs when excess glucose damages the blood vessels in the retina. This eye disease was also linked to a higher risk of dementia. In this case, part of the explanation may lie in the vascular damage caused by diabetes in both the eyes and the brain.
• Glaucoma and macular degeneration: Glaucoma damages the optic nerve, which transmits visual information from the eye to the brain. Age-related macular degeneration affects the central part of the retina and makes tasks like reading, recognizing faces, or distinguishing details difficult. In the analyses included by the Lancet Commission, no statistically clear relationship was found between these two diseases and the risk of dementia.