By Krishna Ramanujan

Across the board, the number of Americans who develop Alzheimer’s disease and other dementias increases with age.  But for African Americans, the risk is much greater – twice as high when compared to whites, according to a special report on race, ethnicity and Alzheimer’s Disease published this year by the Alzheimer’s Association.

The report, which is part of the association’s 2010 Alzheimer’s Disease Facts and Figures, cites greater exposure to risk factors ­­– such as high blood pressure, diabetes, low socioeconomic status, and lower education levels –­ as the main cause of the discrepancies.

“Cognitive impairment and higher rates of dementia and Alzheimer’s Disease in African Americans is not explained by things innate in that group,” said Mary Haan, adjunct professor of epidemiology and biostatistics at the University of California–San Francisco, who was part of an expert panel convened for the special report.

Among other findings, the report reveals that Alzheimer’s and its hallmark of memory loss accounts for 60 to 80 percent of all dementias in the United States. African Americans aged 71 and older are almost twice as likely as their white counterparts to develop Alzheimer’s and other dementias, with 21 percent afflicted compared to 11 percent of whites.  Older Hispanics were 1.5 times more likely to acquire these dementias when compared to older whites, although the data was scarcer for this group.

Discrepancies in cognitive impairment, which is less severe but associated with increased risk for dementia, exist between minority groups and whites as well. Between the ages of 55 and 64, African Americans were four times more likely to be cognitively impaired, and Hispanics almost three as likely as whites.  As individuals aged, more became mentally impaired within all groups, and the gap in rates between the races decreased slightly.  For example, between the ages of 65 to 74, 2.9 percent of whites, 9.3 percent of Hispanics, and 12.4 percent of African Americans were diagnosed as cognitively impaired in the national sample.  After age 85, these numbers rose to 26.9 percent of whites, 44.8 percent of Hispanics, and 54.6 percent of African Americans.

According to the report, the reasons behind these differences cannot be explained by genetics.  Only a small percentage of Alzheimer’s disease cases are inherited from one or both parents through a rare mutation in a gene called ApoE.   Studies show inheritance of this gene does not account for the greater prevalence of Alzheimer’s and other dementias in African Americans or Hispanics, according to the report.  Instead, the evidence points to other potential causes.  African Americans had higher rates of high blood pressure and diabetes than whites, and Hispanics had higher rates of diabetes.  Hypertension is associated with heart disease and increased risk of strokes, which damage small blood vessels in the brain and depending on the location in the brain, can increase the risk of cognitive impairment.  This in turn can lead to Alzheimer’s and other dementias, Haan said.

Diabetes can increase the risk of stroke and damage to micro-vessels in the brain.  Studies show an increased risk of Alzheimer’s in people who are diabetic, even if they are not hypertensive, Haan said.  Obesity, which is also higher for African Americans, is a risk factor for hypertension and diabetes.  And, it may also influence the brain aside from these disorders.  “Being obese may have a direct relationship to dementia and Alzheimer’s disease,” she added.

Socioeconomics – including low income, being raised in a rural setting, and low education levels – are also linked to cognitive impairment, Alzheimer’s, and other dementias.  The report stated that there was an even greater risk for dementia in people with more than one of these characteristics.  Haan said that “socioeconomic levels are differentially distributed by race and ethnicity, at least in this country, and those who are discriminated against are likely to be at a lower level of socioeconomics.”

The findings in the report stem mainly from the Aging, Demographics, and Memory study (ADAMS), the only nationally representative study of Alzheimer’s and other dementias in whites and African Americans older than 71. ADAMS is a subset of the larger 2006 Health and Retirement Study conducted by the Institute for Social Research Survey Research Center at the University of Michigan.