High cholesterol levels in midlife — even cholesterol levels considered only borderline elevated — significantly increases the risk of Alzheimer's disease 30 years later, results of a large study indicate.

"This is the first study, to our knowledge, to show that not only high cholesterol, but also borderline high cholesterol, is associated with dementia," Dr. Rachel Whitmer, the study's senior author, noted in a telephone interview with Reuters Health.

"We need to start thinking about risk factors for dementia in middle age, and cholesterol is a risk factor for dementia that is somewhat modifiable," said Whitmer, a research scientist and epidemiologist at the Kaiser Permanente Division of Research in Oakland, California.

She noted that studies have shown that treatment with a cholesterol-lowering statin drug may lower the risk of dementia. Thus, it seems, "what's good for the heart is good for the mind," Whitmer said.

The study, published in the journal Dementia and Geriatric Cognitive Disorders, involved 9,844 men and women whose cholesterol levels were determined between 1964 and 1973 when they were 40 to 45 years old.

Between 1994 and 2007, a review of their medical records showed that 469 had Alzheimer's disease and 127 had vascular dementia, the second most common form of dementia after Alzheimer's disease, which is caused by clogged blood vessels and other conditions affecting the blood supply to the brain.

Compared to people with "desirable" cholesterol levels below 200 milligrams per deciliter of blood (mg/dL) in midlife, the risk of Alzheimer's disease three decades later was 57 percent higher in people with high midlife cholesterol levels of 240 mg/dL and above.

"Borderline" high cholesterol (200 to 239 mg/dL) tended to increase the risk of Alzheimer's disease as well, but the results were not statistically significant.

However, midlife borderline high cholesterol increased the risk of vascular dementia by 50 percent. High midlife cholesterol also tended to increase the risk of this type of dementia.

These findings, Whitmer noted in a prepared statement, are "disturbing, considering that nearly 100 million Americans have either high or borderline cholesterol levels."

"The study," Whitmer told Reuters Health, "really speaks to (the need for) earlier identification of risk factors and earlier treatment — whether that treatment is a statin or a change in diet or lifestyle."

SOURCE: Dementia and Geriatric Cognitive Disorders, August 2009.