Causes of Alzheimer's Disease

What Causes AD?

Scientists do not yet fully understand what causes AD. There probably is not one single cause, but several factors that affect each person differently. Age is the most important known risk factor for AD. The number of people with the disease doubles every 5 years beyond age 65.

Family history is another risk factor. Scientists believe that genetics may play a role in many AD cases. For example, early-onset familial AD, a rare form of AD that usually occurs between the ages of 30 and 60, is inherited. The more common form of AD is known as late-onset. It occurs later in life, and no obvious inheritance pattern is seen in most families. However, several risk factor genes may interact with each other and with non-genetic factors to cause the disease. The only risk factor gene identified so far for late-onset AD is a gene that makes one form of a protein called apolipoprotein E (ApoE). Everyone has ApoE, which helps carry cholesterol in the blood. Only about 15 percent of people have the form that increases the risk of AD. It is likely that other genes also may increase the risk of AD or protect against AD, but they remain to be discovered.

Research Continues

The NIA-sponsored AD Genetics Study (PDF, 196K) seeks to learn more about risk factor genes for late onset AD.

Scientists still need to learn a lot more about what causes AD. In addition to genetics and ApoE, they are studying education, diet, and environment to learn what role they might play in the development of this disease. Scientists are finding increasing evidence that some of the risk factors for heart disease and stroke, such as high blood pressure, high cholesterol, and low levels of the vitamin folate, may also increase the risk of AD. Evidence for physical, mental, and social activities as protective factors against AD is also increasing.

Can Alzheimer's Be Prevented?

These days, it seems that newspapers, magazines, and TV are full of stories about ways to stay healthy, eat right, and keep fit. Lots of people are concerned about staying healthy as they get older. They wonder whether they can do anything to prevent diseases that happen more often with age, such as Alzheimer’s disease (AD). AD has no known cure, and the secrets to preventing it are not yet known. But research supported by the National Institute on Aging (NIA) and other public and private agencies offers tantalizing clues about the origins and development of AD. These findings are raising hopes that someday it might be possible to delay the onset of AD, slow its progress, or even prevent it altogether. Delaying by even 5 years the time when AD symptoms begin could greatly reduce the number of people who have the disease.

The National Institute on Aging, part of the Federal Government’s National Institutes of Health, has primary responsibility for research on AD and age-related decline in cognitive abilities (such as thinking, decision-making, and language skills). This responsibility is part of a larger mission to understand the nature of aging and find ways to help people stay physically, emotionally, and cognitively healthy for as long as possible.

Several years ago, NIA, the National Institute of Mental Health, and the National Institute of Neurological Disorders and Stroke launched The Cognitive and Emotional Health Project, which has begun to identify and describe the diverse lifestyle factors that possibly affect the emotional health and cognitive abilities of older adults. Further research on the most promising factors will be necessary to determine whether any will result in strategies that can help people remain mentally and emotionally vibrant as they age. The hope is that successful strategies will also contribute to our knowledge of what goes wrong in the brain during the development of neurodegenerative diseases like AD.