Alzheimer’s Disease: Overview and Risk Factors

Alzheimer’s disease is the most common form of dementia in the United States, affecting about 5 million Americans.

Its causes have not been fully elucidated. However, it is known that affected patients accumulate abnormal deposits in their brains, called beta amyloid plaques, as well as disorganized protein fibers, called neurofibrillary tangles. Alzheimer’s disease is also associated with the death of certain brain cells that normally produce a neurotransmitter called acetylcholine, and the main part of the brain–the cerebral cortex–diminishes in size.

Early stages of the disease can be mild, and may not appear any different from the typical signs of aging. However, advanced disease is generally associated with severe memory loss and changes in mental abilities, personality, and behavior. The affected person may show confusion, difficulty with language, and difficulty concentrating, and may even experience hallucinations.

Although Alzheimer’s disease does not directly cause death, life expectancy after diagnosis is decreased by as much as 50 percent. Patients often die from infections, such as pneumonia or urinary tract infections.

Risk Factors

Older persons, women, and African–Americans tend to develop Alzheimer’s at higher rates. Evidence suggests that Alzheimer’s disease is associated with the following:

• Older age: Age is clearly an important factor in the development of this disease. Few people younger than 60 have the disease, but more than half of people older than 90 are affected. As the American population continues to live longer, scientists estimate that the number of patients with Alzheimer’s disease will triple by 2050.
  
• Family history: The chance of developing the disease is increased by 10 to 30 percent in individuals who have an affected first–degree relative. Risk is particularly high if the condition was known to start at a young age. A specific gene, called apolipoprotein E epsilon 4, appears to be involved, and other genes may also contribute.
  
• Elevated cholesterol: High levels of low–density (LDL, or “bad”) cholesterol are associated with an increased risk. In a study of more than 1,000 postmenopausal women, individuals with the highest LDL cholesterol levels had nearly double the risk of developing Alzheimer’s disease, compared with individuals with lower LDL levels.
  
• Existing medical conditions: Several disorders have been associated with a greater risk of developing Alzheimer’s disease, including obesity, diabetes, “pre–diabetes,” hypertension, and cardiovascular disease.
  
• Smoking and excessive alcohol use may increase the risk.

Other factors that may be associated with the development of Alzheimer’s disease include a history of depression and a history of severe head injury.