They estimated that, together, these risk factors account for 17 million cases of Alzheimer's worldwide (about half of the estimated 34 million cases of dementia globally) and 3 million of the 5.3 million estimated U.S. cases.
Some factors appeared to have a greater impact on Alzheimer's risk than others. The UCSF team estimated that worldwide, 19 percent of Alzheimer's cases were attributable to low education, 14 percent to smoking, 13 percent to physical inactivity, 10 percent to depression, 5 percent to mid-life hypertension, 2.4 percent to diabetes and 2 percent to obesity.
In the United States, 21 percent of cases could be traced to low physical activity, 15 percent to depression, 11 percent to smoking, 8 percent to mid-life hypertension, 7 percent to mid-life obesity, 7 percent to low education and 3 percent to diabetes.
Healthy circulation in the brain is thought to be key to keeping the mind sharp, and numerous studies have tied common heart risk factors, such as obesity or hypertension, to an increased risk for dementia. But the researchers stressed that the risk factors included in this analysis have not been shown to actually cause Alzheimer's, only to be associated with it.
One expert agreed with that. "Links have been seen where the presence of a particular risk factor is associated with a higher likelihood of having Alzheimer's and these associations are not necessarily causal," said Dr. Marc L. Gordon, chief of neurology at Zucker Hillside Hospital and an Alzheimer's researcher with the Feinstein Institute for Medical Research in Manhasset, N.Y., who was not involved with the research.
In a second report presented at the meeting, researchers found that older individuals who had less stress, anxiety, depression and trauma -- even in the face of tragic events or circumstances such as a life-threatening illness -- were less likely to develop Alzheimer's.
A team led by Dr. Susanne Stein
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