Risk for Alzheimer's disease in African-American and Caribbean Hispanic seniors is twice that of whites
Ethnic differences in Alzheimer's risk are significant even when other diseases are taken into account
Researchers at Columbia University College of Physicians & Surgeons, Columbia's Mailman School of Public Health, and the New York State Psychiatric Institute have found that the risk for developing Alzheimer's is elevated in African-Americans and Caribbean Hispanics.
This increased risk remained even when researchers took into account the subjects' history of stroke, hypertension, heart disease, or diabetes, as well as level of education or literacy, which the researchers previously found to be associated with Alzheimer's. Dr. Richard Mayeux, Gertrude H. Sergievsky Professor of Neurology and Psychiatry at Columbia and co-director of the Taub Institute for Research on Alzheimer's Disease and the Aging Brain, and colleagues published their report in the January issue of Neurology.
Dr. Mayeux's team tracked the incidence rate of Alzheimer's disease among a sample of Medicare recipients in northern Manhattan over a seven-year period. Previous studies examining risks for Alzheimer's disease and other forms of dementia among various ethnic groups were inconsistent in controlling for risk for stroke and cardiovascular disease and have disagreed on whether African-Americans and Hispanics showed higher risks than whites.
The authors previously reported differences in prevalence of Alzheimer's, or how many seniors had Alzheimer's when the study was conducted. However, such a difference in prevalence could be affected by ethnic differences in how long those afflicted survive with the disease.
The current study, which examines incidence rates, or how frequently the disease occurs among ethnic groups, shows that Caribbean Hispanic and African-American seniors also acquire Alzheimer's disease more often than whites. Says Dr. Mayeux, "It's hard to argue with these incidence findings, because it can't be affected by differences in longevity."
The mechanisms that account for the ethnic differences for developing Alzheimer's are unknown. Other researchers have attributed elevated rates of Alzheimer's in African-Americans to ethnic differences in diseases affecting blood vessels of the brain, but the northern Manhattan study does not support an ethnic difference in incidence of dementia stemming from these causes.
Because no known differences in environmental exposure could account for such differences in Alzheimer's disease, Dr. Mayeux suggests that the origins of such differences between ethnic groups are probably genetic, although the responsible genes have yet to be identified.
While African-Americans and Hispanics show a higher frequency of the epsilon4 version of the APOE gene, a known risk factor for developing Alzheimer's, the authors suggest it's unlikely to explain the difference. "Even when you compare African-Americans and Caribbean Hispanics [without the APOE epsilon4 gene] with white populations without the APOE epsilon4 gene, the African-Americans and Caribbean Hispanics still have a higher propensity for developing Alzheimer's," says Dr. Mayeux.
Ethnic differences in tendency to develop Alzheimer's disease have implications for public health officials as they project the numbers of Alzheimer's patients requiring care in the future. Says Dr. Mayeux: "Both the immigration of Caribbean Hispanics and increases in life expectancy among African-Americans have raised the proportions of these ethnic groups among the senior population. It is therefore likely that we will have even more people affected by Alzheimer's than we might otherwise have predicted."