Age

Increasing age is the greatest known risk factor for Alzheimer's. Alzheimer's is not a part of normal aging, but your risk increases greatly after you reach age 65. The rate of dementia doubles every decade after age 60.

People with rare genetic changes linked to early-onset Alzheimer's begin experiencing symptoms as early as their 30s.

Family history and genetics

Your risk of developing Alzheimer's appears to be somewhat higher if a first-degree relative — your parent or sibling — has the disease. Scientists have identified rare changes (mutations) in three genes that virtually guarantee a person who inherits them will develop Alzheimer's. But these mutations account for less than 5 percent of Alzheimer's disease.

Most genetic mechanisms of Alzheimer's among families remain largely unexplained. The strongest risk gene researchers have found so far is apolipoprotein e4 (APoE4), though not everyone with this gene goes on to develop Alzheimer's disease. Other risk genes have been identified but not conclusively confirmed.

Down syndrome

Many people with Down syndrome develop Alzheimer's disease. 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. A gene contained in the extra chromosome that causes Down syndrome significantly increases the risk of Alzheimer's disease.

Sex

Women seem to be more likely than are men to develop Alzheimer's disease, in part because they live longer.

Mild cognitive impairment

People with mild cognitive impairment (MCI) have memory problems or other symptoms of cognitive decline that are worse than might be expected for their age, but not severe enough to be diagnosed as dementia.

Those with MCI have an increased risk — but not a certainty — of later developing dementia. Taking action to develop a healthy lifestyle and strategies to compensate for memory loss at this stage may help delay or prevent the progression to dementia.

Past head trauma

People who've had a severe head trauma seem to have a greater risk of Alzheimer's disease.

Lifestyle and heart health

There's no lifestyle factor that's been definitively shown to reduce your risk of Alzheimer's disease.

However, some evidence suggests that the same factors that put you at risk of heart disease also may increase the chance that you'll develop Alzheimer's. Examples include:

• Lack of exercise
• Obesity
• Smoking or exposure to secondhand smoke
• High blood pressure
• High blood cholesterol
• Poorly controlled type 2 diabetes
• A diet lacking in fruits and vegetables

These risk factors are also linked to vascular dementia, a type of dementia caused by damaged blood vessels in the brain. Working with your health care team on a plan to control these factors will help protect your heart — and may also help reduce your risk of Alzheimer's disease and vascular dementia.

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.