MONDAY, May 23, 2005 (HealthDay News) -- High cholesterol is generally considered a risk factor for dementia, although studies examining that connection have yielded conflicting results.

Now a new study in the May 24 issue of the journal Neurology suggests that high cholesterol levels in old age may reduce dementia risk.

One possible explanation is that high cholesterol plays a protective role against dementia in the elderly, the study's U.S. and Swedish authors speculate. Alternatively, high levels of this waxy substance in the body could be a marker for older people who are more robust and somehow less vulnerable to cholesterol's adverse effects, they say.

"These findings raise more questions than they give answers," conceded Michelle M. Mielke, a researcher with the Center on Aging and Health at Johns Hopkins Bloomberg School of Public Health, and one of the study authors. "Therefore," she said, "we strongly urge that consumers not make changes in their diet or medication without consulting with their doctors first."

Rachel Whitmer, a research scientist at Kaiser Permanente Northern California who specializes in cognitive aging, agreed. "Lingering questions were not put to rest" by the new study, "but new exciting ones are raised." The study is unique because several measures of cholesterol were taken during old age, not simply at a single point in time, she noted.

"This study is another example of the importance of timing in terms of when one measures a risk factor, and the need to consider risk factors for dementia over the entire life course," Whitmer said.

Mielke said further research is needed because the study raises questions with important implications.

"On the one hand, finding that high cholesterol in the elderly is protective for dementia would be a big step forward in finding ways to prevent or delay the onset of the disease, as well as identifying new potential mechanisms underlying the pathology," she noted. "On the other hand, if high cholesterol is a marker of robustness in old age, this finding would also be important because it could help us to identify what makes these individuals invulnerable to developing dementia and other illnesses."

Although people think of cholesterol as something that's bad for you, it is essential for many physiologic functions, including the maintenance of cell membranes and maintaining proper brain functioning. Almost everyone makes enough cholesterol to meet these needs, so they don't need more of it in their diet. However, according to Mielke, the metabolic processes involved are different in the elderly. Studies suggest low cholesterol may be detrimental to aging cells.

To understand the link between cholesterol and dementia, the authors analyzed data from 392 men and women, all 70-year-old residents of Goteborg, Sweden. At the start of the research and in follow-up visits over an 18-year period, participants had a series of assessments performed, including a physical, an EKG, a chest X-ray, a battery of blood tests and a neuropsychiatric examination. At ages 85 and 88, testing also included an interview and a CT scan.

Participants who died or did not participate in follow-up exams were traced through health records, the nation's hospital system or death certificates. In this way, the authors were able to obtain data for all individuals in the study.

Of the 392 original participants, 10 had dementia at the first assessment and were excluded from the study. Of the remaining 382 participants, 93 went on to develop dementia.

The study found high total cholesterol levels at ages 70 and 75 were associated with a reduced risk of dementia between ages 75 and 79. Higher levels at 70, 75 and 79 were associated with a reduced risk between ages 79 and 88.

The relationship between cholesterol and dementia may vary considerably depending on when measured over a person's life or in the course of the disease, the authors noted.

"It is becoming more and more apparent that we cannot rely on simple answers; for example, that high cholesterol is always bad and low cholesterol is always good," Mielke said. "It may depend on when a person has high cholesterol."

In a separate study in the same journal, Israeli researchers found a link between family history of dementia and hallucinations in Parkinson's disease. Researchers used questionnaires to determine the presence of hallucinations, a common occurrence in patients being treated for the neurologic condition. Medical records and interviews were used to determine family history of Parkinson's and dementia.

Hallucinations occurred in 32 percent of the 276 patients in the study. "Whether hallucinations are related to genetic predispositions or share common risk factors associated with dementia remains unclear," the authors noted.

More information

The American Academy of Family Physicians can tell you about the common signs of dementia.

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