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Published on: December 16, 2010
by Roni Caryn Rabin for The New York Times:
Could HDL cholesterol — the good kind linked to lower heart disease risk — also protect people from dementia?
A new study reports that older New York City residents who had very high blood levels of high-density lipoprotein, or HDL, the so-called “good” cholesterol, were at less than half the risk of developing dementia over time than those with the lowest levels.
The people who reaped the benefit had very high HDL blood levels that exceeded 56 milligrams per deciliter of blood, the study reported. They developed 60 percent fewer cases of Alzheimer’s disease than people with the lowest HDL levels, of 38 milligrams or below. The differences between the two groups held even after the researchers adjusted the figures to account for other causal factors that influence the development of dementia, like vascular disease, as well as age, sex, education level and genes that predispose to Alzheimer’s.
“We think it’s a causal relationship,” said Dr. Christiane Reitz, the study’s lead author and an assistant professor of neurology at Columbia University’s Taub Institute for Research on Alzheimer’s Disease and the Aging Brain. “At the baseline, when we recruited these people, they didn’t have cognitive problems. We followed them, and they developed dementia during the follow-up period.”
But the HDL was only protective at extremely high levels, Dr. Reitz said. “It really only makes a difference if you’re higher than 56 [milligrams],” she said.
The report, published in the Archives of Neurology, is not the first to find that what’s good for the body may also good for the brain. Numerous studies have found that older people who walked the most were at lowest risk of developing vascular dementia, possibly because the regular exercise improves cerebral blood flow and lowers the risk of vascular disease.
Regular physical activity, in general, is believed to improve brain function, both by increasing blood flow to the brain and by stimulating the production of hormones and nerve growth factors involved in new nerve cell growth. Exercise also raises levels of “good” HDL cholesterol. Studies have found that animals that are kept physically active have better memories and more cells in their hippocampus, a part of the brain critical for memory. And exercise can help stave off or keep in check diseases like Type 2 diabetes, which increase the risk of developing dementia.
The Columbia researchers have been following several large, ethnically diverse groups of older New Yorkers for several years now to identify patterns in the development of dementia. The group covered in this study included a random sampling of 1,130 adults from northern Manhattan, all of whom were Medicare beneficiaries 65 and over, with no history of dementia or cognitive impairment at the beginning of the study. The scientists collected data from medical, neurological and neuropsychological evaluations. Over the course of the study, 101 new cases of Alzheimer’s disease were diagnosed; the average age of the individuals who developed the condition was 83.
Dr. Reitz says the exact mechanism whereby HDL cholesterol may protect people from dementia is unclear. High HDL can protect people from stroke, and strokes are a strong risk factor for Alzheimer’s disease, she said. Likewise, people with diabetes often have high total cholesterol levels, high blood pressure and obesity, all of which are risk factors for Alzheimer’s disease.
But HDL may also have an independent effect on Alzheimer’s risk, she said, because it may be involved in helping to clear the beta amyloid protein that accumulates in the brain in those with the condition.
Some medications, like niacin and fibrates, may help raise HDL levels, Dr. Reitz said. But she recommends a Mediterranean diet rich in healthy fats from nuts, fish and olive oil, along with exercise, adding, “Aerobic exercise helps a lot.”
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