What causes dementia, including Alzheimer's, remains a mystery, but research suggests that while genetic factors are likely to play a role, some environmental factors increase the risk. It follows that lifestyle measures may reduce it. These include not smoking, being physically active, eating a balanced, healthy diet, maintaining good cardiovascular health, and exercising the brain.
Even healthy factors not traditionally linked to dementia, such as vision, hearing, or how well dentures fit may affect the risk.
Exercise can protect the heart, and possibly the brain, too.
People with cardiovascular problems appear to be more likely to develop dementia.
There is evidence that bad heart habits, such as smoking and a diet high in saturated fats, may reduce brain volume.
Autopsies have detected cardiovascular disease in 80 percent of people with Alzheimer's, although the link does not mean that one caused the other.
Some patients who have the hallmark Alzheimer's plaques and tangles never develop symptoms. It may be that symptoms only appear if the patient also has some kind of vascular disease.
Vascular dementia occurs when blood vessels which provide the brain with oxygen are damaged, depriving the brain of oxygen.
This suggests that controlling cardiovascular risk factors could help to prevent the development of Alzheimer's.
Research has suggested that dementia is 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.
Metabolic syndrome can be prevented or treated with good diet, exercise, weight loss, and some medications. Reducing weight, blood pressure, and cholesterol can cut the risk not only of diabetes and cardiovascular events, but also dementia and Alzheimer's disease.
Several studies have found that people who were overweight or obese in their midlife years were more likely to develop Alzheimer's or vascular dementia.
A study 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 healthy and well-balanced diet helps keep the brain healthy, because it improves heart health, and a healthy heart provides the brain with plenty of oxygen-rich blood. Heart disease risk scores have been closely linked to the likelihood of cognitive decline.
The Mediterranean diet might help to protect the aging brain.
The Mediterranean diet, with olive oil as the main source of fat, plenty of fruits, vegetables, and limited meat and dairy produce, is said to protect aging brains and prevent vascular dementia.
Evidence suggests that the Mediterranean diet is more effective than a low-fat diet in protecting the brain health of older people.
Other research has found that eating baked or broiled fish once a week reduces the risk of Alzheimer's disease and mild cognitive impairment. Participants who did so "had better preservation of gray matter volume on MRI in brain areas at risk for Alzheimer's disease."
Physical fitness and regular exercise from a younger age are likely to lower the risk of developing vascular dementia and Alzheimer's disease.
This could be due to a better blood and oxygen supply to the brain, but also because it benefits cardiovascular health, a risk factor for dementia.
However, de Fina's team notes that the results were the same, whether or not a person had previously had a stroke.
As late adulthood approaches the brain's hippocampus starts to shrink, leading to a loss of memory and a higher risk of dementia. One study has shown that a year of moderate physical exercise can reverse this shrinkage and improve spatial memory.
The hippocampus is part of the limbic system and is located deep within the brain tissue. It is important for several types of memory formation and spatial navigation.
Researchers in Japan called for exercise to be given priority in preventing Alzheimer's, after concluding that exercise alone may be as effective as exercise plus diet in reducing β-amyloid formation, 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. Not only formal exercise, but cooking, washing the dishes, and cleaning can help.
Not only in older age, but the offspring of mothers who exercised during pregnancy appear to be less likely to develop neurodegenerative diseases, including Alzheimer's, in later life.
This may be due to epigenetic changes in the underlying DNA during gestation, which means that mothers pass their experience on to their children.
Dr. Eric Ahlskog, of the Mayo Clinic, concludes: "You can make a very compelling argument for exercise as a disease-modifying strategy to prevent dementia and mild cognitive impairment, and for favorably modifying these processes once they have developed."
Keeping an active mind
Several studies suggest that the risk of cognitive decline is much lower if the brain is kept mentally active and people maintain strong social connections.
Brain-stimulating activities and games may help to prevent dementia.
One research team found that retiring later reduced the chances of dementia. Their study found that employees who retired at the age of 65 were 14 percent less likely to be diagnosed with Alzheimer's compared to 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 can help to preserve memory in old age. People who regularly take part in activities that exercised their brain score better in tests that measured thinking and memory.
Scientists have shown that individuals who keep their brains active throughout their lives have lower levels of the the β-amyloid protein, which plays a major role in amyloid plaque buildup in Alzheimer's disease.
One study team has found that people who are bilingual may need to experience twice as much brain damage for Alzheimer's to appear, compared with speaking just one language.
Others have observed 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.
Getting plenty of good quality sleep can offer significant protection from memory loss, dementia, and Alzheimer's disease.
Disrupted sleep has been associated 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 did not sleep badly. However, more research is needed in this area.
Some studies have linked smoking and nicotine with cognitive decline, especially in males, but others have not. This could be due to the increased risk of stroke and heart disease, also risk factors for Alzheimer's, among smokers.