More than 100 years after Alzheimer’s disease was first characterized, scientists have excellent knowledge about the causes of Alzheimer’s disease. Age is the most important risk factor for Alzheimer’s disease. The number of people with the disease doubles every five years beyond age 65.
Statistically speaking, about 5% of men and women between the ages of 65 and 74 have Alzheimer’s disease, and nearly half those age 85 and older may have the disease. Despite its prevalence, Alzheimer’s disease is not a normal part of aging.
Family history indicates an increased risk, but genetic mutations play a dominant role in less than 1% of cases. Scientists found a rare, early-onset familial form that usually occurs between ages 30 and 60. The most common form is late-onset, usually occurring to people in their late 70s. It is believed that risk factor genes may interact with non-genetic factors to cause the disease.
The only risk factor gene specifically identified for late-onset Alzheimer’s disease is one form of a protein called apolipoprotein E (ApoE). Everyone has ApoE which helps carry cholesterol in the bloodstream, but only about 15% of people have the form ApoE4 that significantly increases the risk of Alzheimer’s disease. Scientists believe that other genes may increase risk of the disease or protect against it, but those genes have yet to be identified.
In addition to genetics and ApoE, education, diet and environment play a role in the disease. Scientists are finding evidence that Alzheimer’s disease shares risk factors with heart disease and stroke, such as high blood pressure, diabetes and high cholesterol. Lifestyle factors such as exercise, social interaction, mental attitude, nutrition, head trauma and stress have been linked to Alzheimer’s disease. Evidence is mounting that physical, mental and social activities may act as protective factors.