What causes Alzheimer’s?
Experts agree that in the vast majority of cases, Alzheimer's, like other common chronic conditions, probably develops as a result of complex interactions among multiple factors, including age, genetics, environment, lifestyle, and coexisting medical conditions. Although some risk factors — such as age or genes — cannot be changed, other risk factors — such as high blood pressure and lack of exercise — usually can be changed to help reduce risk. Research in these areas may lead to new ways to detect those at highest risk.
A small percentage of people with Alzheimer’s disease (less than 1 percent) have an early-onset type associated with genetic mutations. Individuals who have these genetic mutations are guaranteed to develop the disease. An ongoing clinical trial conducted by the Dominantly Inherited Alzheimer Network (DIAN), is testing whether antibodies to beta-amyloid can reduce the accumulation of beta-amyloid plaque in the brains of people with such genetic mutations and thereby reduce, delay or prevent symptoms. Participants in the trial are receiving antibodies (or placebo) before they develop symptoms, and the development of beta-amyloid plaques is being monitored by brain scans and other tests.
Another clinical trial, known as the A4 trial (Anti-Amyloid Treatment in Asymptomatic Alzheimer’s), is testing whether antibodies to beta-amyloid can reduce the risk of Alzheimer’s disease in older people (ages 65 to 85) at high risk for the disease. The A4 trial is being conducted by the Alzheimer’s Disease Cooperative Study.
Catalyst to progress
In 2014, the Alzheimer’s Association awarded $8 million to researchers in Massachusetts to conduct a companion study to the A4 trial known as LEARN (Longitudinal Evaluation of Amyloid Risk and Neurodegeneration). The LEARN study will follow over time older people who do not have beta-amyloid plaques in the brain to determine what brain changes are associated with cognitive decline.
Learn more about the drug treatment horizon
Several conditions known to increase the risk of cardiovascular disease — such as high blood pressure, diabetes and high cholesterol — also increase the risk of developing Alzheimer's. Some autopsy studies show that as many as 80 percent of individuals with Alzheimer's disease also have cardiovascular disease.
A longstanding question is why some people develop hallmark Alzheimer's plaques and tangles but do not develop the symptoms of Alzheimer's. Vascular disease may help researchers eventually find an answer. Some autopsy studies suggest that plaques and tangles may be present in the brain without causing symptoms of cognitive decline unless the brain also shows evidence of vascular disease. More research is needed to better understand the link between vascular health and Alzheimer’s.
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Physical exercise and diet
Regular physical exercise may be a beneficial strategy to lower the risk of Alzheimer's and vascular dementia. Exercise may directly benefit brain cells by increasing blood and oxygen flow in the brain Because of its known cardiovascular benefits, a medically approved exercise program is a valuable part of any overall wellness plan.
Current evidence suggests that heart-healthy eating may also help protect the brain. Heart-healthy eating includes limiting the intake of sugar and saturated fats and making sure to eat plenty of fruits, vegetables, and whole grains. No one diet is best. Two diets that have been studied and may be beneficial are the DASH (Dietary Approaches to Stop Hypertension) diet and the Mediterranean diet. The DASH diet emphasizes vegetables, fruits and fat-free or low-fat dairy products; includes whole grains, fish, poultry, beans, seeds, nuts, and vegetable oils; and limits sodium, sweets, sugary beverages, and red meats. A Mediterranean diet includes relatively little red meat and emphasizes whole grains, fruits and vegetables, fish and shellfish, and nuts, olive oil and other healthy fats.
Catalyst to progress
The Alzheimer's Association was among the first to encourage investigation of the impact of vascular factors on Alzheimer's disease. We have funded such studies for more than 20 years and continue to highlight this promising avenue of research into potentially modifiable risk factors. Learn more about our commitment to research.
Social connections and intellectual activity
A number of studies indicate that maintaining strong social connections and keeping mentally active as we age might lower the risk of cognitive decline and Alzheimer's. Experts are not certain about the reason for this association. It may be due to direct mechanisms through which social and mental stimulation strengthen connections between nerve cells in the brain.
Catalyst to progress
Animal studies can be especially helpful in increasing our knowledge about direct mechanisms through which physical and mental stimulation may benefit the brain. Orly Lazarov, PhD, received a 2007 Alzheimer's Association New Investigator Research Grant to explore the impact of physical activity and an enriched environment on mice genetically engineered to carry one of the human genes that causes Alzheimer's disease. Her results showed that physical and mental stimulation appear to decrease hallmark Alzheimer's pathologies and support new nerve cell growth and better cell-to-cell communication.
There appears to be a strong link between future risk of Alzheimer's and serious head trauma, especially when injury involves loss of consciousness. You can help reduce your risk of Alzheimer's by protecting your head.
- Wear a seat belt
- Use a helmet when participating in sports
- "Fall-proof" your home
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What you can do now
While research is not yet conclusive, certain lifestyle choices, such as physical activity and diet, may help support brain health and prevent Alzheimer's. Many of these lifestyle changes have been shown to lower the risk of other diseases, like heart disease and diabetes, which have been linked to Alzheimer's. With few drawbacks and plenty of known benefits, healthy lifestyle choices can improve your health and possibly protect your brain.
Learn more about brain health.
You can help increase our knowledge by considering participation in a clinical study. Prevention and risk management studies need healthy participants who are willing to make a long-term commitment to moving the field forward. You can find prevention trials currently recruiting volunteers through TrialMatch®, our free clinical trial matching service.
Understanding prevention research
Here are some things to keep in mind about the research underlying much of our current knowledge about possible prevention:
- Insights about potentially modifiable risk factors apply to large population groups, not to individuals. Studies can show that factor X is associated with outcome Y, but cannot guarantee that any specific person will have that outcome. As a result, you can "do everything right" and still have a serious health problem or "do everything wrong" and live to be 100.
- Much of our current evidence comes from large epidemiological studies such as the Honolulu-Asia Aging Study, the Nurses' Health Study, the Adult Changes in Thought Study and the Kungsholmen Project. These studies explore pre-existing behaviors and use statistical methods to relate those behaviors to health outcomes. This type of study can show an "association" between a factor and an outcome but cannot "prove" cause and effect. This is why we describe evidence based on these studies with such language as "suggests," "may show," "might protect," and "is associated with."
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- The gold standard for showing cause and effect is a clinical trial in which participants are randomly assigned to a prevention or risk management strategy or a control group. Researchers follow the two groups over time to see if their outcomes differ significantly.
- It is unlikely that some prevention or risk management strategies will ever be tested in randomized trials for ethical or practical reasons. One example is exercise. Definitively testing the impact of exercise on Alzheimer's risk would require a huge trial enrolling thousands of people and following them for many years. The expense and logistics of such a trial would be prohibitive, and it would require some people to go without exercise, a known health benefit.
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Selected reports and resources
- "The Healthy Brain Initiative: A National Public Health Road Map to Maintaining Cognitive Health"
The Centers for Disease Control and Prevention and the Alzheimer's Association, 2007. (70 pages)
The Alzheimer's Association and the Centers for Disease Control and Prevention convened a multidisciplinary steering committee and a panel of invited experts to establish a plan to make brain health part of our national wellness agenda.
- "Preventing Alzheimer's Disease and Cognitive Decline: Evidence Report/Technology Assessment Number 193."
Williams, John W., Plassman, Brenda L., et al. Agency for Healthcare Research and Quality, Department of Health and Human Services, April 2010.
This expert panel convened by the National Institutes of Health (NIH) evaluated the strength of evidence for a wide range of risk factors implicated in Alzheimer's disease, including nutritional issues, medical conditions and prescription and non-prescription medications, social/economic/behavioral factors, toxic environmental influences, and genetics. Although there is consistent evidence linking many factors to reduced risk, the panel concluded that evidence is not yet strong enough to recommend any specific strategies to prevent Alzheimer's disease.
- "The NIH Cognitive and Emotional Health Project: Report of the Critical Evaluation Study Committee."
Hendrie, Hugh C.; Albert, Marilyn S.; Butters, Meryl A.; et al. Alzheimer's & Dementia: The Journal of the Alzheimer's Association, January 2006; Vol. 2 (1): 12–32.
An expert panel appointed by the National Institutes of Health (NIH) to assess current scientific knowledge about brain health and identify promising areas for further research finds that heart health, physical activity, freedom from chronic illness and a strong social support system may all help maintain mental sharpness and emotional well-being as we age. The panel identifies more than 40 factors that may influence cognitive and emotional health in older adults. Some of the most consistent findings link high blood pressure, diabetes, stroke and excess weight to an increased risk of cognitive decline.
- "Achieving and Maintaining Cognitive Vitality with Aging."
Fillitt, Howard M.; Butler, Robert N.; O'Connell, Alan. W.; Albert, Marilyn S.; and others. Mayo Clinic Proceedings 2002; 77: 681 – 696.
Co-sponsored and reviewed by the National Institute on Aging (NIA), this overview article summarizes recent research assessing the impact of various lifestyle factors and medical conditions on the health of the aging brain. Includes an extensive reference list.
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