High levels of the so-called "good" cholesterol may lower the risk of developing Alzheimer's disease, according to a new study.
In the study, those with high levels of high-density lipoprotein (HDL), the good kind of cholesterol , were 60 percent less likely to develop Alzheimer's disease than those with lower HDL levels.
"The higher your HDL, the more protected you are from Alzheimer's disease , apparently," said study researcher Dr. Christiane Reitz, of Columbia University.
The researchers found no evidence that high levels of "bad" cholesterol, known as low-density lipoprotein (LDL), affected a person's risk of Alzheimer's.
Because the study included only participants from a single urban area, more research needs to be done to see if the findings apply to the general population, the researchers said.
The good, the bad, and the Alzheimer's
Cholesterol is transported around the body by proteins known as lipoproteins. LDL is known as "bad" cholesterol because at high levels, it can clog blood vessels and hinder blood flow. On the other hand, HDL is thought to carry cholesterol to the liver, where it can be broken down and removed from the blood, according to the American Heart Association.
In the new study, Reitz and her colleagues examined the cholesterol levels of 1,130 adults ages 65 or older living in northern Manhattan, New York City. The subjects began the study between 1999 and 2001, and every 18 months, they underwent a number of medical, psychological and neurological tests to measure their cholesterol levels and check for Alzheimer's disease. None of the participants had Alzheimer's at the study's start.
Because Alzheimer's can be officially diagnosed only after an autopsy — which allows physicians to confirm the presence of plaques in the brain — the participants with signs of the disease were said to have either probable or possible Alzheimer's.
After about 4 years, 101 participants developed Alzheimer's, 89 of which were probable cases.
Those with high HDL levels were less likely than those with low HDL levels to have both probable and possible Alzheimer's. The link held even after the researchers accounted for factors that could have influenced the results, such as age, gender, genetic predisposition to Alzheimer's and whether the subjects were taking cholesterol-lowering drugs .
How it might work
While the researchers don't know exactly how high HDL levels might prevent Alzheimer's, there are possible explanations. They noted that high HDL levels are also associated with a decreased risk of having a stroke, and strokes are known to increase the risk of Alzheimer's.
It's also possible HDL helps clear the plaque-forming protein from the brain, Reitz said.
While previous studies have looked at the link between cholesterol levels and risk of dementia, results have been mixed.
The new study is published in the December issue of the journal Archives of Neurology.
Pass it on: High levels of "good" cholesterol may protect against Alzheimer's disease.
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