Seven risk factors for Alzheimer’s disease unveiled
It looks like half of all Alzheimer’s disease cases are linked to seven, well-defined risk factors, and controlling them could significantly reduce one’s chances for developing the disease, according to researchers from UC San Francisco and the San Francisco VA Medical Center, who published their findings today in the journal Lancet Neurology. Modifying the risk factors could help bring down the number of cases diagnosed each year – numbers that keep going up as the Baby Boom generation enters the retirement years.
The greatest risk factor worldwide is lack of education – specifically not completing high school. The leading risk factor in the United States, where higher education is more common, is a sedentary lifestyle.
About 35 million people are thought to suffer from the disease, including nearly 6 million cases in the United States. As the population grows older still, the worldwide total is predicted to triple by the year 2050.
Worldwide, lack of education contributed 19% of the risk, 14% came from smoking, 13% from lack of physical activity, 10% from depression, 5% from high blood pressure at midlife, 2% from diabetes and 2% from obesity.
Lack of exercise was the primary risk factor in the United States, accounting for 21% of risk. Depression accounted for 15%, smoking for 11%, hypertension for 8%, obesity for 7%, low education for 7% and diabetes for 3%.
the study's lead author, psychiatrist Deborah Barnes of the VA, said that since about a third of the U.S. population is sedentary, that fact could help explain the steep 21% risk in Alzheimer’s.
Barnes and other Alzheimer’s researchers are cautious about attributing cause to the risk factors. In other words, no one knows exactly how these risk factors are related to the development of the disease. What is known is that the seven risk factors studied are also related to vascular dementia, a type of cognitive decline caused by damaged blood vessels in the brain. Many people with cognitive decline have brain changes characteristic of both Alzheimer's disease and vascular dementia. Some researchers think that each condition helps fuel the damage caused by the other.
Alzheimer’s disease is caused by the buildup of a protein plaque called beta amyloid in brain tissue. The sticky beta amyloid accumulates between brain neurons and interferes with communication between axons. Eventually, it appears to cause neuron degeneration and cell death. No one knows beta amyloid’s exact mechanism of action; however, its presence is always indicative of the disease. It may be that damage to brain tissue, which may come as a result of a sedentary lifestyle and its health consequences, enables beta amyloid proliferation.
If that is true, researchers will be faced with explaining another mystery: how leading a mentally and socially active lifestyle helps offset Alzheimer’s risk. Studies have also found a link between being mentally challenged and decreased occurrence of the disease.
Factors that may reduce risk of Alzheimer's disease include:
• Higher levels of formal education
• A stimulating job
• Mentally challenging leisure activities, such as reading, playing games or playing a musical instrument
• Frequent social interactions
Scientists are stumped about how this might work. One theory suggests that the stimulated brain develops more cell-to-cell connections, which protects it against the impact of Alzheimer-related changes. Another theory holds that it may be harder to measure cognitive decline in people who exercise their minds frequently or who have more education. Still another explanation is that people with Alzheimer's disease may be less inclined to seek out stimulating activities years before their disease can be diagnosed.