Alzheimer's disease and its precursor, mild cognitive impairment, appear to be associated with an increased risk of death among both white and African American older adults according to a new, long-term research study by neurological experts at the Alzheimer's Disease Center at Rush University Medical Center.
Data from two earlier national surveys have suggested that life expectancy among patients with Alzheimer's disease may be greater for African Americans than for whites, according to Robert Wilson, PhD, a neuropsychologist at the Alzheimer's Disease Center at Rush and the study's lead author.
"In these surveys, the diagnosis of Alzheimer's disease is not based on a uniform clinical evaluation but derived from medical records, which increases the likelihood of substantial variation in the quality of diagnostic classifications," said Wilson.
However, the results from this study show that the presence and severity of mild cognitive impairment and Alzheimer's disease are associated with reduced survival among African Americans and these effects are comparable to those seen among whites, according to Wilson.
Alzheimer's disease reduces life expectancy and has emerged as a leading cause of death in the United States. "There is limited knowledge about the consequences of mild cognitive impairment and Alzheimer's disease in African Americans," said Wilson. "In this study we evaluated the risk of death among both African Americans and whites in an urban community during a 10 year follow-up."
Rush researchers evaluated the risk of death associated with incident Alzheimer's disease and diagnoses were based on a uniform, detailed clinical evaluation. They also examined survival rates among participants with mild cognitive impairment.
A total of 1,715 older adults (average age 80.1, 52.5 percent African American) who came from four adjacent neighborhoods in Chicago participated in the study. Each participant had a clinical evaluation that included medical history, a neurological examination and cognitive function testing, which analyzes thinking, learning and memory.
Based on these evaluations, an experienced physician diagnosed 296 (17.3 percent) of participants with Alzheimer's disease, 597 (34.8 percent) with mild cognitive impairment and 20 (1.2.) percent with other forms of dementia, while 802 (46.80 percent had no cognitive impairment.
During the 10-year follow-up (average observation period 4.7 years) 634 individuals died (37 percent), including 25.8 percent of those without cognitive impairment, 40.4 percent of those with mild cognitive impairment, 59.1 percent of those with Alzheimer's disease and 60 percent of those with other forms of dementia.
"Compared with people without cognitive impairment, risk of death was increased by about 50 percent among those with mild cognitive impairment and was nearly three-fold greater among those with Alzheimer's disease," said Wilson. "These effects were seen among African Americans and whites and did not differ by race."
Among individuals with mild cognitive impairment, risk of death increased as cognitive impairment became more severe, another association that did not differ by race. A similar association between disease severity and survival was seen among patients with Alzheimer's disease, although that effect was slightly stronger for African Americans than whites.
"Overall, these results do no suggest strong racial differences in survival for persons with mild cognitive impairment and Alzheimer's disease," said Wilson. "If there are racial differences, it will be important to determine whether they are due to diagnostic bias or whether they reflect actual differences in the underlying neurobiology of the disease or in how affected individuals are cared for."
- Robert S. Wilson; Neelum T. Aggarwal; Lisa L. Barnes; Julia L. Bienias; Carlos F. Mendes de Leon; Denis A. Evans. Biracial Population Study of Mortality in Mild Cognitive Impairment and Alzheimer Disease. Arch Neurol, 2009;66(6):767-772 [link]
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