Increasing age is the greatest known risk factor for Alzheimer's disease. Alzheimer's is not a part of normal aging, but as you grow older the likelihood of developing Alzheimer's disease increases.
One study, for example, found that annually there were four new diagnoses per 1,000 people ages 65 to 74, 32 new diagnoses per 1,000 people ages 75 to 84, and 76 new diagnoses per 1,000 people age 85 and older.
Family history and genetics
Your risk of developing Alzheimer's is somewhat higher if a first-degree relative — your parent or sibling — has the disease. Most genetic mechanisms of Alzheimer's among families remain largely unexplained, and the genetic factors are likely complex.
One better understood genetic factor is a form of the apolipoprotein E gene (APOE). A variation of the gene, APOE e4, increases the risk of Alzheimer's disease. Approximately 25% to 30% of the population carries an APOE e4 allele, but not everyone with this variation of the gene develops the disease.
Scientists have identified rare changes (mutations) in three genes that virtually guarantee a person who inherits one of them will develop Alzheimer's. But these mutations account for less than 1% of people with Alzheimer's disease.
Many people with Down syndrome develop Alzheimer's disease. This is likely related to having three copies of chromosome 21 — and subsequently three copies of the gene for the protein that leads to the creation of beta-amyloid. Signs and symptoms of Alzheimer's tend to appear 10 to 20 years earlier in people with Down syndrome than they do for the general population.
There appears to be little difference in risk between men and women, but, overall, there are more women with the disease because they generally live longer than men.
Mild cognitive impairment
Mild cognitive impairment (MCI) is a decline in memory or other thinking skills that is greater than normal for a person's age, but the decline doesn't prevent a person from functioning in social or work environments.
People who have MCI have a significant risk of developing dementia. When the primary MCI deficit is memory, the condition is more likely to progress to dementia due to Alzheimer's disease. A diagnosis of MCI encourages a greater focus on healthy lifestyle changes, developing strategies to make up for memory loss and scheduling regular doctor appointments to monitor symptoms.
People who've had a severe head trauma have a greater risk of Alzheimer's disease. Several large studies found that in people age 50 years or older who had a traumatic brain injury (TBI), the risk of dementia and Alzheimer's disease increased. The risk increases in people with more-severe and multiple TBIs. Some studies indicate that the risk may be greatest within the first six months to two years after the TBI.
Studies in animals have indicated that air pollution particulates can speed degeneration of the nervous system. And human studies have found that air pollution exposure — particularly from traffic exhaust and burning wood — is associated with greater dementia risk.
Excessive alcohol consumption
Drinking large amounts of alcohol has long been known to cause brain changes. Several large studies and reviews found that alcohol use disorders were linked to an increased risk of dementia, particularly early-onset dementia.
Poor sleep patterns
Research has shown that poor sleep patterns, such as difficulty falling asleep or staying asleep, are associated with an increased risk of Alzheimer's disease.
Lifestyle and heart health
Research has shown that the same risk factors associated with heart disease may also increase the risk of Alzheimer's disease. These include:
- Lack of exercise
- Smoking or exposure to secondhand smoke
- High blood pressure
- High cholesterol
- Poorly controlled type 2 diabetes
These factors can all be modified. Therefore, changing lifestyle habits can to some degree alter your risk. For example, regular exercise and a healthy low-fat diet rich in fruits and vegetables are associated with a decreased risk of developing Alzheimer's disease.
Lifelong learning and social engagement
Studies have found an association between lifelong involvement in mentally and socially stimulating activities and a reduced risk of Alzheimer's disease. Low education levels — less than a high school education — appear to be a risk factor for Alzheimer's disease.