MONDAY, Dec. 13 (HealthDay News) -- Sticking to a heart-healthy lifestyle may also ward off Alzheimer's disease, according to a new study that suggests that raising "good" cholesterol levels can help prevent the brain disorder in older people.

The study, published in the December issue of Archives of Neurology, found that people who had low levels of high-density lipoprotein (HDL) or "good" cholesterol had a 60 percent greater risk of developing Alzheimer's disease after the age of 65 than those who had high levels.

Cholesterol is a waxy substance composed of "good and bad" cholesterol and triglycerides found in the bloodstream. More than 50 percent of the U.S. population has high levels of "bad" cholesterol, according to the study.

"Our study suggests that high HDL levels ['good' cholesterol] are associated with a lower risk for Alzheimer's disease," said Dr. Christiane Reitz, the study's author. "Ways to increase HDL levels include losing weight [if overweight], aerobic exercise and a healthy diet."

By treating problems with cholesterol levels, "we can lower the incidence of Alzheimer's disease in the population," said Reitz.

Some medications, such as statins, fibrates and niacin, that are used to lower "bad" cholesterol also raise "good" cholesterol, said Reitz, an assistant professor of neurology at Columbia University's Taub Institute for Research on Alzheimer's Disease in New York City.

More than 5 million Americans have Alzheimer's disease, the most common form of dementia, and those numbers could triple by 2050, according to health officials.

The U.S. National Institutes of Health reports that about 5 percent of Americans between the ages of 65 and 74 have late-onset Alzheimer's disease, the more common form of the disorder, and the prevalence increases with age. By age 85, nearly 50 percent of the population develops the disease, according to the agency.

Early-onset Alzheimer's, a rare form of the disease, begins in middle age and runs in families. Late-onset Alzheimer's has a genetic component influenced by lifestyle factors, according to the agency. There is no cure for Alzheimer's disease, but a few drugs can help reduce symptoms for a time, according to experts.

However, people can cut their risk by reducing their intake of trans-fats and increasing monounsaturated fats that keep "good" cholesterol high and "bad" cholesterol low, said Reitz, noting that drinking moderate amounts of alcohol also helps. Foods high in monounsaturated fats include vegetable oils, avocados, peanut butter and many nuts and seeds.

The 1,130 study participants were drawn from a random sample of Medicare recipients in New York City. The participants were screened for Alzheimer's, and those with symptoms were excluded. Screening for the study began in 1999 and follow-ups were conducted every 18 months until the data was analyzed in 2010.

Participants also underwent a battery of tests measuring mental functions, such as memory, language processing, visual-spatial orientation and executive function. Executive function allows people to comprehend instructions and complete a given task.

During the study, 101 cases of Alzheimer's disease were identified, at an average age of 83 years.

One weakness of the research is that it was conducted among elderly residents of an urban community with a high prevalence of risk factors, such as obesity, cardiovascular disease and diabetes, according to the study. The findings may not apply to a younger, healthier population.

One expert on the disease, Catherine M. Roe of Washington University in St. Louis, said it was already known that "good" cholesterol benefits the heart, but this study shows "an additional reason to make sure we live a healthy lifestyle."

"These results are important because they suggest that an increase in HDL cholesterol may also help ward off Alzheimer's disease," said Roe, a research assistant professor at the school's Knight Alzheimer's Disease Research Center.

The study is strong because it used a large random sample of elderly people, Roe added. But she cautioned that the results need to be duplicated.

However, "since the authors did not find an effect of HDL cholesterol in their previous, similar study, I think we have to be cautious about these results until they are also demonstrated in other samples," Roe noted.

In addition to eating a healthy diet, getting exercise and losing weight as recommended by Reitz, Roe said that quitting smoking could help people increase levels of "good" cholesterol.

"I think it's a great idea to talk with your doctor about what you specifically can do to live the healthiest lifestyle you can," Roe suggested.

More information

To learn more about cholesterol levels, visit the American Heart Association.