MONDAY, Sept. 12 (HealthDay News) -- New research suggests that high cholesterol levels could boost the risk of Alzheimer's disease by creating more brain-clogging bits known as plaque.

The finding doesn't directly prove that high cholesterol causes Alzheimer's disease or that lowering it would reduce the risk. Also, researchers didn't find any link between high cholesterol and tangles, which also clog the brain in those with Alzheimer's.

Still, the findings add to previous research that has linked insulin resistance to Alzheimer's disease, said study author Dr. Kensuke Sasaki. Better control of both cholesterol levels and insulin resistance, both risk factors for heart disease, "might contribute to a strategy for the prevention of Alzheimer's disease," said Sasaki, an assistant professor of neuropathology at Kyushu University in Japan.

An estimated 5.4 million Americans have Alzheimer's disease, according to the Alzheimer's Association, and the number is expected to grow to 16 million by 2050 as the population ages. There's no known way to prevent Alzheimer's or cure it.

The researchers studied the brains of 147 people -- 76 men, 71 women -- who were residents of a Japanese town and alive in 1988 when they underwent clinical examinations. They all underwent autopsies between 1998 and 2003.

About one-third of them had been diagnosed with dementia during life, although they didn't show signs of it in 1988.

Compared with people with low cholesterol levels, those with high cholesterol levels were more likely to have the bits of protein in the brain known as plaques: 62 percent versus 86 percent, respectively.

But tangles, which are bits of another kind of protein, weren't more common in people with high cholesterol.

Dr. Marc L. Gordon, chief of neurology at the Zucker Hillside Hospital in Glen Oaks, N.Y., said the research is credible and intriguing. It adds to existing speculation that higher cholesterol levels in midlife, particularly of so-called "bad" cholesterol, boost the risk of Alzheimer's later, said Gordon, who's also an Alzheimer's researcher at the Feinstein Institute for Medical Research.

It's not clear how cholesterol may make plaques more common, Gordon said, although cholesterol is found in plaques. It's possible that high cholesterol could set off another process that causes Alzheimer's, he said, or that something else "predisposes you to be prone to Alzheimer's and raises your cholesterol level."

There's a twist: cholesterol levels and obesity appear to drop in people who have dementia, although that may have something to do with changes in their eating habits, Gordon noted.

The study is published in the Sept. 13 issue of the journal Neurology.

More information

For more about Alzheimer's disease, try the U.S. National Library of Medicine.