A low level of “good” cholesterol is a well-known risk factor for heart disease. A new study by investigators at Columbia University College of Physicians & Surgeons now suggests that a low level of good cholesterol may also raise the risk of developing Alzheimer's disease.
“Low levels of 'good' cholesterol (a.k.a. high-density lipoproteins or HDL) are very common in the United States,” says the study's lead author, Christiane Reitz, MD, PhD, assistant professor of neurology (in the Sergievsky Center and Taub Institute). “If raising HDL can lower a person's risk of developing Alzheimer's disease, that means we may be able to significantly reduce the rate of Alzheimer's disease in the population,” Reitz says, though she cautions that the finding still must be confirmed in other studies.
The study, which appears in the December issue of Archives of Neurology, is co-authored with Jose Luchsinger, MD, MPH, associate professor of medicine and epidemiology, and Richard Mayeux, MD, director of the Gertrude Sergievsky Center and Sergievsky Professor of Neurology, Psychiatry, and Epidemiology.
Previously, the relationship between HDL and Alzheimer's disease had been unclear. Some studies found an association, but others, including one of Reitz's own, found no connection. The new study, Reitz says, follows subjects for a longer period of time than previous studies, resulting in a more accurate account of the number of subjects who ultimately develop Alzheimer's.
After monitoring 1130 elderly residents of northern Manhattan for an average of four years, the researchers found a 40 percent higher incidence of Alzheimer's in residents with low HDL (less than 55 mg/dl). The reason that low HDL is associated with a higher rate of Alzheimer's isn't understood. One possibility is that it works through stroke. “We know low HDL raises the risk of stroke and that stroke is associated with Alzheimer's, so stroke may be the mediator,” Reitz says. “But there's also evidence that HDL works by itself to clear amyloid proteins [the proteins believed to cause Alzheimer's] from the brain.”
Because the study included a large number of African Americans and Hispanics, unlike previous studies that focused on whites, the finding may indicate that low HDL is linked to a high risk of Alzheimer's in many different ethnicities.