February 10, 2016, KAISER PERMANENTE -- In the largest and longest study thus far of ethnic disparities in dementia risk, researchers compared six ethnic and racial groups within the same geographic population and found significant variation in dementia incidence among them. The results are published online today in Alzheimer's & Dementia: The Journal of the Alzheimer's Association.

This is the first study to look at dementia risk in a large population representing the diversity of the United States. Researchers found dementia incidence to be highest in blacks and American Indian/Alaska Natives, lowest among Asian Americans, and intermediate among Latinos, Pacific Islanders and whites.

The researchers found that dementia incidence over the study period ranged from an average annual rate of 26.6 cases per 1,000 for blacks, and 22.2 cases per 1,000 for American Indians/Alaskan Natives, to 15.2 cases per 1,000 for Asian Americans. In between were Latinos and Pacific Islanders with an average annual rate of 19.6 cases per 1,000, and whites with 19.3 per 1,000.

Using cumulative risk estimates, researchers projected that among those who reach age 65 dementia-free, 38 percent of blacks, 35 percent of American Indians/Alaskan Natives, 32 percent of Latinos, 30 percent of whites, 28 percent of Asian Americans and 25 percent of Pacific Islanders would develop dementia in the next 25 years.

"Most research on inequalities in dementia includes only one to two racial and ethnic groups, primarily whites and blacks," said lead author Elizabeth Rose Mayeda, PhD, postdoctoral fellow at University of California, San Francisco in the Department of Epidemiology and Biostatistics. "This is the only research that directly compares dementia for these six racial and ethnic groups, representing the true aging demographic of the United States in a single study population."

The study population included more than 274,000 Northern California members of Kaiser Permanente, the nation's largest private integrated health care system with more than 10 million members. The researchers used electronic health records covering patient visits over 14 years -- from January 2000 through December 2013 -- to identify participants diagnosed with dementia, as well as their race and ethnicity. The dementia diagnoses were Alzheimer's, vascular dementia or non-specific dementia.

"Even in the lowest risk groups in the study, the lifetime risk of developing dementia is high -- in every racial and ethnic group, over one in four people who survive to age 65 can expect to be diagnosed with dementia in their lifetime," said Rachel Whitmer, PhD, the principal investigator of the study and a research scientist at the Kaiser Permanente Division of Research. Whitmer has an extensive research portfolio in aging epidemiology, specifically in predictors of cognitive decline and dementia, and population-level risk factors including metabolic, cardiovascular and inflammatory factors.

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