Alzheimer's disease is the most common cause of dementia. Scientists do not know what causes it, so there is no way to prevent it. However, some long-term lifestyle measures might help.

Alzheimer's affects around 5.7 million people in the United States, and researchers expect the numbers to grow as people live for longer.

What causes most forms of dementia, including Alzheimer's, remains a mystery. Genetic factors may play a role, but environmental factors might increase the chance of developing symptoms, especially in those who have specific genetic features.

If so, some lifestyle measures may reduce the risk. A systematic review published in 2016 suggested that people can reduce their risk of dementia by not smoking, being physically active, eating a balanced, healthy diet, maintaining good cardiovascular health, and exercising the brain.

Early diagnosis and prevention of chronic diseases and conditions, such as hypertension, high blood pressure, high blood cholesterol, diabetes, obesity in mid-life, and depression may also help.

In addition, some factors that experts have not traditionally linked to dementia may contribute. These include vision, hearing, skin health, how well a person's dentures fit, and others. However, evidence of exact links, or how they work, is limited.

At a conference of the American Academy of Neurology (AAN) in 2011, researchers noted that people with fewer overall health problems had a lower likelihood of developing dementia in the long term.

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A healthful diet may help prevent cardiovascular problems and dementia later in life.

People with cardiovascular problems appear to have a higher chance of developing some forms of dementia.

Conditions that people often have before Alzheimer's include:

These can also underlie other forms of dementia, such as vascular dementia.

There is evidence that bad heart habits, such as smoking and a diet high in saturated fats, may reduce brain volume.

Autopsies have found cardiovascular disease in 80 percent of people with Alzheimer's, although the link does not mean that one caused the other.

Some people have the hallmark Alzheimer's plaques and tangles, but they never develop symptoms. It may be that symptoms only appear in these people if they also have some kind of vascular disease.

Vascular dementia occurs when there is damage in the blood vessels that provide the brain with oxygen. As a result, low levels of oxygen reach the brain.

Controlling cardiovascular risk factors may help to prevent the development of Alzheimer's.

However, some people develop Alzheimer's without having any cardiovascular symptoms.

Dementia appears to be more likely to emerge in people with metabolic syndrome, a cluster of conditions that includes obesity, high blood pressure, high cholesterol, and high blood sugar levels.

A study of 3,458 people, published in the Journal of the American Heart Association (JAHA) in 2017, supported this finding. The researchers noted, however, that the link between the two remains unclear.

Lifestyle measures that can help to prevent or treat metabolic syndrome include:

  • a good diet
  • exercise
  • weight control
  • some medications

Maintaining a healthy weight, blood pressure, and cholesterol levels may cut the risk not only of diabetes and cardiovascular events but also dementia and Alzheimer's disease.

Several studies have found that people who had excess weight or obesity in their midlife years were more likely to develop Alzheimer's or vascular dementia later in life.

Research from Kyushu University in Fukuoka, Japan, found in 2011 that people with diabetes had significantly higher odds of developing Alzheimer's and other dementias, including vascular dementia. Good diabetes control may lower the risk.

A healthful, well-balanced diet helps keep the brain healthy, because it improves heart health. A healthy heart provides the brain with plenty of oxygen-rich blood.

Scientists have linked heart disease risk scores with the likelihood of cognitive decline.

The Mediterranean diet may help to protect aging brains and prevent vascular dementia.

It includes:

  • olive oil as the main source of fat
  • plenty of fruits
  • vegetables
  • limited meat and dairy produce

In 2014, a team of nutritionists noted that the Mediterranean diet may help prevent cardiovascular and cognitive problems as people get older.

In 2013, other research showed that people aged over 70 years who ate more than 2,100 calories a day almost doubled their risk of mild cognitive impairment. Cognitive impairment is the loss of ability to reason and think.

A study published in 2012 found that diets high in omega-3 fatty acids and vitamins C, B, D, and E may improve mental ability, while a diet high in trans fats appears to encourage brain shrinkage.

Eating baked or broiled fish once a week may reduce the risk of Alzheimer's disease and mild cognitive impairment, according to a study published in 2014. Participants who ate fish once a week "had better preservation of gray matter volume on MRI in brain areas at risk for Alzheimer's disease."

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Keeping physically fit boosts cardiovascular health and may lead to better mental health in later life, too.

A person who engages in physical fitness and regular exercise from a younger age may have a lower risk of developing vascular dementia and Alzheimer's disease, according to a 2013 study.

One theory is that exercise benefits cardiovascular health—a risk factor for dementia—and boosts the supply of blood and oxygen to the brain.

As people approach late adulthood, part of the brain known as the hippocampus starts to shrink. This leads to a loss of memory and a higher risk of dementia.

Findings published in 2011 suggested that a year of moderate physical exercise may reverse this shrinkage and improve spatial memory.

The hippocampus is part of the limbic system. It is located deep within the brain tissue. It is important for several types of memory formation and spatial navigation.

In 2012, researchers in Japan called for doctors to prioritize exercise as a way of preventing Alzheimer's after a mouse study suggested that exercise alone may be as effective as exercise plus diet in reducing beta-amyloid formation. This formation is a defining characteristic of Alzheimer's disease.

Even if a person starts exercising after the age of 80 years, they may reduce their risk of Alzheimer's, according to results of a study of 71 people, published in 2012. Not only formal exercise, but cooking, washing the dishes, and cleaning can help.

Children born to mothers who exercised during pregnancy may also be less likely to develop neurodegenerative diseases, including Alzheimer's, in later life. This was the conclusion of a mouse study carried out in 2011.

A review published in 2011 notes that aerobic exercise, in particular, may reduce the risk of cognitive decline, possibly because it keeps the brain's blood vessels healthy.

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Keeping an active mind may help to prevent cognitive decline as people get older.

Several studies suggest that the risk of cognitive decline is lower if a person:

  • keeps their brain mentally active
  • maintains strong social connections

Retiring later may reduce the chances of dementia, according to researchers who analyzed data for 429,803 pensioners in France.

They found that employees who retired at the age of 65 years were 14 percent less likely to have a diagnosis of Alzheimer's, compared with those who retired at 60 years.

This supports the "use it or lose it" hypothesis.

Playing games, writing, reading and engaging in a range of brain-stimulating activities may help to preserve memory in old age. Research published in 2013 found that people who regularly took part in activities that exercised their brain score better in tests that measured thinking and memory.

Individuals who keep their brains active throughout their lives appear to have lower levels of the beta-amyloid protein, a protein that contributes to amyloid plaque buildup in Alzheimer's disease, according to a 2012 study.

In 2012, one research team concluded that people who are bilingual may need to experience twice as much brain damage for Alzheimer's to appear, compared with those who speak just one language.

As long ago as 2003, a study of 469 people found that anything that challenges the mind, such as playing an instrument, chess, or bridge, could reduce the risk of dementia by up to 63 percent.

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People who have uninterrupted sleep may be less likely to develop dementia later in life.

Good-quality sleep might offer significant protection from memory loss, dementia, and Alzheimer's disease.

Scientists have associated disrupted sleep with a buildup of amyloid plaques.

People who do not wake up often during the night may be five times less likely to have amyloid plaque build-up, compared with those who wake often.

However, it is not clear whether early features of Alzheimer's cause sleep disruption or if disrupted sleep contributes to the condition.

There is growing evidence that smoking contributes to cognitive decline.

A long-term Korean study involving 46,140 men aged 60 years and over found that those who had never smoked or who had quitted for 4 years or more had a lower risk of developing Alzheimer's and other types of dementia. The team published their results in 2018.

One reason might be that smoking increases the risk of cardiovascular disease, which is a risk factor for Alzheimer's.

Some people have developed Alzheimer's after a traumatic brain injury (TBI) or repeated blows to the head, for example, while playing football.

In 2018, some researchers explored a link between TBI, dementia, and vascular dysfunction. They concluded that there may be a link whereby a TBI results in dementia because it damages the blood vessels in the brain.

People who participate in contact sports and other activities that involve a risk of TBI should wear protective gear. They should also be sure to see a doctor and have plenty of rest after any TBI that they experience.

For the same reason, it is also essential to wear a safety belt when travelling in a car and a suitable crash helmet on a motorcycle or when cycling.

Scientists do not know what causes Alzheimer's disease. Genetic factors probably play a role, but environmental factors might contribute.

Eating healthfully throughout life, avoiding smoking, and keeping mentally and physically fit may help to reduce the risk in some people.