Alzheimer's Disease: Risk Factors
Scientists have identified factors that appear to play a role in the development of Alzheimer’s disease, but no definitive causes have been found for this complex disorder.
Known Risk Factors
Age
The single greatest risk of developing Alzheimer’s disease is age. Approximately 5 percent of Americans between the ages of 65 and 74, and almost half of those 85 years and older are estimated to have Alzheimer's.
Genetics
The majority of Alzheimer’s cases are late-onset, usually developing after age 65, and this form of the disease shows no obvious inheritance pattern. However, in some families, clusters of cases are seen. A gene called Apolipoprotein E (ApoE) appears to be a risk factor for the late-onset form of Alzheimer’s. There are three forms of this gene: ApoE2, ApoE3 and ApoE4. Roughly one in four Americans has ApoE4 and one in twenty has ApoE2. While inheritance of ApoE4 increases the risk of developing the disease, ApoE2 substantially protects against it. Some current research is focused on the association between these two forms of ApoE and Alzheimer's disease. Several other genes also appear to influence the development of Alzheimer’s disease, and more detailed information is available in the Heredity section. Familial Alzheimer’s disease (FAD) or early-onset Alzheimer's is an inherited, rare form of the disease, affecting less than 10 percent of patients. Familial Alzheimer's Disease develops before age 65, in people as young as 35. It is caused by one of three gene mutations on chromosomes 1, 14 and 21.
Potential Contributing Factors
Cardiovascular disease
Risk factors associated with heart disease and stroke, such as high blood pressure and high cholesterol, may also increase one's risk of developing Alzheimer's disease. High blood pressure may damage blood vessels in the brain, disrupting regions that are important in decision-making, memory and verbal skills. This could contribute to the progression of the disease. High cholesterol may inhibit the ability of the blood to clear protein from the brain.
Type 2 Diabetes
There is growing evidence of a link between Alzheimer's disease and type 2 diabetes. In Type 2 diabetes insulin does not work effectively to convert blood sugar into energy. This inefficiency results in production of higher levels of insulin and blood sugar which may harm the brain and contribute to the progression of Alzheimer's.
Oxidative Damage
Free radicals are unstable molecules that sometimes result from chemical reactions within cells. These molecules seek stability by attacking other molecules, which can harm cells and tissue and may contribute to the neuronal brain cell damage caused by Alzheimer's.
Inflammation
Inflammation is a natural, but sometimes harmful, healing bodily function in which immune cells rid themselves of dead cells and other waste products. As protein plaques develop, inflammation results, but it is not known whether this process is damaging and a cause of Alzheimer's, or part of an immune response attempting to contain the disease.
Other Possible Risk Factors
Some studies have implicated prior traumatic head injury, lower education level and female gender as possible risk factors. Alzheimer's disease may also be associated with an immune system reaction or a virus.