Dementia risk varies by ethnicity
Northern California study finds blacks have highest incidence among 6 groups
The risk of being diagnosed with Alzheimer’s disease or other forms of dementia is significantly higher in some racial or ethnic groups than it is in others, according to results announced Wednesday of the largest and longest study to look at the issue.
The study tracked more than 274,000 Northern California Kaiser Permanente members over 14 years, encompassing six
racial or ethnic groups, and found that among the patients African Americans had the highest incidence of dementia-related disease. Their risk was 65 percent higher than that of Asian Americans, who had the lowest rates of memory-robbing disease.
American Indians and Alaska Natives also had a higher dementia risk, followed by Latinos, Pacific Islanders and whites.
“It’s telling there are these large differences in people who have equal access to care. The next big question is why,” said Rachel Whitmer, principal investigator of the study and a research scientist at the Kaiser Permanente Division of Research. “If we can study the lowest- risk groups and the highest- risk groups … we will come away with information that will help everybody.”
Dementia declining
The study, conducted by Kaiser and UCSF researchers and published online in the Alzheimer’s Association journal Alzheimer’s & Dementia, was one of two important large, long- term papers released Wednesday about the incidence of Alzheimer’s disease and other dementias in an aging population.
The other, a study in the New England Journal of Medicine, was based on data from the decades- long Framingham Heart Study, and came away with far more optimistic results.
Researchers, looking at data from more than 5,200 people, found that incidents of dementia declined by 20 percent each decade over the past four decades. The scientists said the decline may be a result of patients taking better care to avoid cardiovascular problems, which increase various risk factors for dementia. That could be a greater use of statins and hypertension drugs, they said.
Role of education?
Higher levels of education also could play a role in decreasing risk for dementia, the Framingham researchers said.
Kaiser’s Whitmer noted some key differences in the research population of the two studies. “The Framingham study is a study of white people, and this is a study with six different racial and ethnic groups,” she said. “It’s really a different story.”
Blacks, whites, Asians, Latinos, Pacific Islanders and American Indian/ Alaska Natives were included in the Kaiser study. Virtually no data on dementia risk in Native Americans or Pacific Islanders existed before the study, and past studies on Asians have focused on Japanese Americans, the researchers said. The Asian group in this study was made up of a range of ethnicities, including Chinese, Japanese and Korean. The Latino group was predominantly made up of Mexican Americans.
Participants included virtually every Kaiser member in Northern California who was at least 64 when the study began in January 2000. They had not been diagnosed with Alzheimer’s, vascular dementia or nonspecific dementia and remained in the Kaiser system throughout the study.
By the time the research ended in December 2013, nearly 22 percent of the participants were diagnosed with dementia, 29 percent had died and 17 percent were lost to follow- up. The average age at diagnosis was 83 years.
There was little variation in the age at which people were diagnosed, but the incidence rate varied greatly among demographics.
Projecting percentages
As part of the study, the researchers created a model based on their findings that projected what percentage of people in each group who reached age 65 without a dementia diagnosis would go on to develop the disease. Among blacks, that figure was 38 percent followed by 35 percent for American Indians and Alaskan Natives. Whites and Latinos had risk levels at about the 30 percent range, while Asians and Pacific Islanders had a risk in the midto upper- 20 percentages range.
The researchers had adjusted the data for a variety of factors, including age, sex, cardiovascular disease, hypertension and depression, but the differences remained. The purpose was to account for such dementia risk factors as, for example, higher rates of hypertension in African Americans. But the adjustments didn’t explain the disparities.
They acknowledged they lacked some key information that could help explain some of the differences — education levels, brain images and whether participants had the gene most closely associated with the development of Alzheimer’s. Additional studies are in the works.
“We had to do this first large study where we could see these disparities,” said Elizabeth Rose Mayeda, postdoctoral fellow at UCSF and lead author of the study. “The next step is to do smaller studies to really understand the mechanism driving these inequalities.”
President’s priority
Keith Fargo, the Alzheimer's Association’s director of scientific programs and outreach, said the study helps advance the understanding of disparities in Alzheimer’s diagnoses, which is a priority of President Obama’s National Plan to Address Alzheimer’s Disease to treat or prevent the disease by 2025.
“To achieve this goal, we need to understand why the risk for Alzheimer’s and dementia is different among ethnic and racial groups,” he said.