Study leader Deborah Barnes, a mental health researcher at the San Francisco VA Medical Center and University of California, San Francisco and colleagues analyzed data from studies worldwide involving hundreds of thousands of participants.
The study, published in The Lancet Neurology and presented at the Alzheimer's Association International Conference on Alzheimer's Disease in Paris, found that worldwide, the biggest modifiable risk factors for Alzheimer's disease are, in descending order of magnitude: low education, smoking, physical inactivity, depression, mid-life hypertension, diabetes and mid-life obesity.
Together, these risk factors are associated with as much as 51 percent of Alzheimer's cases worldwide and 54 percent of Alzheimer's cases in the United States -- 2.9 million cases, Barnes says.
"What's exciting is that this suggests that some very simple lifestyle changes, such as increasing physical activity and quitting smoking, could have a tremendous impact on preventing Alzheimer's and other dementias in the United States and worldwide," Barnes says in a statement.
Barnes cautions her conclusions are based on the assumption that there is a causal association between each risk factor and Alzheimer's disease.
"We are assuming that when you change the risk factor, then you change the risk," Barnes says. "What we need to do now is figure out whether that assumption is correct."