High levels of HDL-cholesterol may
be associated with lower risk of Alzheimer's disease
High levels of high-density lipoprotein (HDL) appear
to be associated with a reduced risk for Alzheimer's disease in older adults,
according to a report in the December issue of Archives of Neurology, one of the
JAMA/Archives journals.
"Dyslipidemia and late-onset Alzheimer's disease are
highly frequent in western societies," the authors write as background information
in the article. "More than 50 percent of the U.S. adult population has high cholesterol.
About 1 percent of people age 65 to 69 years develop Alzheimer's disease, and
the prevalence increases to more than 60 percent for people older than 95 years."
Christiane Reitz, M.D., Ph.D., and colleagues at Columbia
University's Taub Institute, New York, studied 1,130 older adults to examine the
association of blood lipid levels with Alzheimer's disease. The study included
a random sampling of Medicare recipients 65 or older residing in northern Manhattan,
with no history of dementia or cognitive impairment. The researchers defined higher
levels of HDL cholesterol as 55 milligrams per deciliter or more.
To determine this association, data were collected from
medical, neurological and neuropsychological evaluations. Additionally, the authors
assigned a diagnosis of "probable" Alzheimer's disease when onset of dementia
could not be explained by any other disorder. A diagnosis of "possible" Alzheimer's
disease was made when the most likely cause of dementia was Alzheimer's disease
but there were other disorders that could contribute to the dementia, such as
stroke or Parkinson disease.
During the course of follow-up, there were 101 new cases
of Alzheimer's disease, of which 89 were probable and 12 were possible. The mean
(average) age of individuals at the onset of probable and possible Alzheimer's
disease was 83 years, and compared with people who were not diagnosed with incident
Alzheimer's disease, those who did develop dementia were more often Hispanic and
had a higher prevalence of diabetes at the start of the study. Higher plasma levels
of HDL cholesterol were associated with a decreased risk of both probable and
possible Alzheimer's disease, even after adjusting for vascular risk factors and
lipid-lowering treatments. Although higher plasma total cholesterol, non-HDL cholesterol
and LDL cholesterol levels also were associated with decreased risks of probable
and possible Alzheimer's disease, these associations became non-significant after
adjusting for vascular risk factors and lipid-lowering treatments.
"In this study, higher levels of HDL cholesterol were
associated with a decreased risk of both probable and possible Alzheimer's disease,"
the authors conclude. "An important consideration in the interpretation of the
results is that it was conducted in an urban multiethnic elderly community with
a high prevalence of risk factors for mortality and dementia. Thus, our results
may not be generalizeable to cohorts with younger individuals or to cohorts with
participants with a lower morbidity burden."
This study was supported by grants from the National
Institute on Aging, the Charles S. Robertson Memorial Gift for Research in Alzheimer's
Disease and the Blanchette Hooker Rockefeller Foundation.
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