An Indiana University and Regenstrief Institute study is the first to report significantly decreased incidence rates over two decades for Alzheimer's disease and other dementias in African-Americans. The study is also the first to show that the incidence rate of these conditions in Africans was unchanged over the same period.
In African-Americans in Indianapolis, dementia incidence rates declined significantly from 1992 to 2011. However, there was no noteworthy change in dementia incidence in older Yoruba of Ibadan, Nigeria, according to the prospective community-based study of the two populations published online ahead of print in the peer-reviewed Alzheimer's & Dementia: Journal of the Alzheimer's Association.
"The reason for the significant decline in new cases of Alzheimer disease and other dementias in the African-Americans we studied is not yet entirely clear but we believe it may be possible that medications for cardiovascular conditions contributed to the decline," said study first author Sujuan Gao, Ph.D., professor of biostatistics at Indiana University School of Medicine. "This explanation is supported by the fact that prior to the study both groups had similar rates of elevated blood pressure, which had been recognized and treated in the Indianapolis participants but not in those in Ibadan."
This work and other studies, including a landmark JAMA 2001 study from the same research group that determined that African-Americans were twice as likely as Africans to develop dementia, utilized data gathered during the pioneering Indianapolis-Ibadan Dementia Project. Participants in the two cities were evaluated over the two-decade duration of the project or until they developed dementia. To facilitate comparison of the two groups, African-Americans and Africans were evaluated using the same clinical assessment instruments, which the researchers designed specifically for the project.
While the rate of new cases of dementia decreased in Indianapolis over the two decades, the African-Americans enrolling at the midpoint of the project in 2001 had significantly higher rates of medical conditions including diabetes, hypertension and stroke and as well as higher treatment rates for these conditions than the African-Americans who entered the project in 1992.
"The formal and informal costs of care for Alzheimer's and other dementias are enormous now, in some respects greater than those related to heart disease and cancer," said Regenstrief and IU Center for Aging Research investigator Hugh Hendrie, MBChB, D.Sc., senior author of the new study. "With the worldwide demographic trends, the burden is likely to become exponentially greater, particularly in the developing world which is less able to cope.
"The results of this study offer at least a glimmer of hope that preventive measures such as the appropriate treatment of cardiovascular diseases like hypertension, if applied to the developing countries, as well as in developed countries, may modify this burden." Dr. Hendrie is a geriatric psychiatrist who designed and implemented the Indianapolis-Ibadan Dementia Project in collaboration with colleagues from Indiana University and the University of Ibadan.
In addition to Drs. Gao and Hendrie, authors of "Dementia Incidence Declined in African-Americans, but not in Yoruba" are Adesola Ogunniyi, MBChB; Olusegun Baiyewu, MBBS and Oye Gureje, MBBS, Ph.D, D.Sc., of the College of Medicine, University of Ibadan; Kathleen S. Hall, Ph.D.; Frederick W. Unverzagt, Ph.D., Kathleen A. Lane, M.S.; Jill R. Murrell, Ph.D., and Ann M. Hake, M.D. of the IU School of Medicine.
The research was supported by National Institutes of Health grants R01AG09956, R01AG019181, and P30AG10133.