The study indicates people with total cholesterol levels between 249 to 500 milligrams were 1.5 times more likely to develop Alzheimer's disease than people with cholesterol levels of less than 198 milligrams. People with total cholesterol levels of 221 to 248 milligrams were more than 1.25 times more likely to develop Alzheimer's disease.

"High mid-life cholesterol increased the risk of Alzheimer's disease regardless of mid-life diabetes, high blood pressure, obesity, smoking and late-life stroke," study author Dr. Alina Solomon of the University of Kuopio in Finland said in a statement.

Solomon and study senior author Rachel Whitmer of the Kaiser Permanente Division of Research in Oakland, Calif., based their study on 9,752 men and women in northern California who underwent health evaluations between 1964 and 1973 when they were between the ages of 40 and 45 and remained with the same health plan through 1994.

From 1994 to 2007, researchers obtained the participants' most recent medical records to find 504 people had a diagnosis of Alzheimer's disease and 162 had vascular dementia.

The findings are being presented at the American Academy of Neurology annual meeting in Chicago.