Experts say the new study, which was published Monday in the Archives of Neurology, is further evidence of a link between heart disease and dementia, and if the finding is backed by more research, doctors think it may point to a way that people can reduce their risk of both brain and heart trouble later in life, by boosting HDL.
“If you do things for your coronary vascular health, it clearly appears to modify your Alzheimer’s risk as well in a way we don’t completely understand.” says James R. Burke, MD, PhD, associate director of the Bryan Alzheimer’s disease research center at Duke University in Durham, N.C., who was not involved in the study.
“It’s been clearly demonstrated that you can have a big bang for your buck in terms of your heart with HDL, and now there’s initial evidence, at least, that people who have the lowest levels of HDL at least are at a significantly increased of Alzheimer’s disease, and perhaps if you modify that, then you would modify your risk,” Burke says.
HDL and Alzheimer’s Disease
Researchers at Columbia University in New York followed 1,130 seniors who had no history of memory trouble or dementia.
When researchers compared the cholesterol levels of study participants with and without Alzheimer’s, they found that those with the highest HDL counts, over 55 mg/dL, had about a 60% reduced risk of developing the disease compared to those whose levels were under 39 mg/dL.
“Basically, what we found is that higher levels of good cholesterol decrease the risk of Alzheimer’s disease,” says study author Christiane Reitz, MD, PhD, assistant professor of Neurology at Columbia University’s Taub Institute.
Reitz and her team also found that people with high LDL, or “bad” cholesterol, and high total cholesterol had a decreased risk of developing dementia, but when they took into account other conditions known to increase the risk of Alzheimer’s, like diabetes, high blood pressure, obesity, or a genetic predisposition, LDL and total cholesterol were no longer significant predictors in their own right.
“HDL was the only one which actually stayed significant and was not explained by any of the other risks factors,” Reitz says. “For HDL it seems to be an independent association with Alzheimer’s disease with, independent of diabetes, high blood pressure and so on.”
A Complex Role for Cholesterol in the Brain
Reitz says that while she found an association between HDL and this form of dementia, she’s not really sure why it may be protective.
“There’s a lot of research trying to find out why HDL is associated with Alzheimer’s disease and what the biological mechanism is behind that. There are different potential explanations, which we’re trying to find out,” Reitz says. “One is that HDL affects the risk of stroke and stroke is associated with Alzheimer’s disease.”
“HDL is one of the major carriers of protein in the brain,” says Lenore Launer, PhD, chief of the Neuroepidemiology Section in the Intramural Research Program at National Institute on Aging. “HDL can go out of the brain, it can go into the brain, so there is some flux between in and out of the brain, which makes it difficult to say how much of the periphery measurements reflect what’s going on in the brain.”
In 2001, Launer published a study in the journal Neurology that came to the opposite conclusion of the Columbia study. She found that Japanese-American men with higher HDL cholesterol levels were more likely to have Alzheimer’s-related plaques and tangles in their brains.
“I’d like to see some consistency across the literature. And the HDL finding has not been consistent across the literature,” Launer says. “Until the message is pretty consistent across studies, I really wouldn’t have any recommendations about levels of HDL and Alzheimer’s disease.”
Keeping the Heart Healthy May Also Help the Brain
While it may not make sense to boost HDL levels to try to prevent Alzheimer’s disease just yet, Launer and other experts note that higher levels of HDL have clearly been shown to protect the heart, so for that reason alone, they think it’s smart to keep good cholesterol in mind at every checkup.
“I tell everybody, let’s face it, you can lower your risk of heart disease,” says Peter Davies, PhD, director of the Litwin Zucker Research Center for the Study of Alzheimer’s Disease at the Feinstein Institute for Medical Research in Manhasset, N.Y. “If you get your cholesterol under control, with lifestyle modifications and maybe medication, you can reduce your risk of heart disease and I think probably, if you do that, you’ll reduce your risk of Alzheimer’s, too.”
Guidelines recommend that men raise HDL levels that are under 40 mg/dL and that women increase HDL numbers under 50 mg/dL. An HDL of 60 mg/dL or higher is optimal.