THURSDAY, Nov. 11, 2010 (HealthDay News) -- For years, doctors have been saying that keeping your cholesterol levels in check as you age is good for your brain as well as your heart, but a new study suggests the connection between cholesterol and dementia later in life isn't quite so clear-cut.
After more than 1,400 Swedish women followed for 32 years, Johns Hopkins researchers found that those with high cholesterol at mid-life were at no greater risk of developing Alzheimer's and other types of dementia than women with lower levels. In addition, the women whose cholesterol levels decreased the most from middle to older age were 2.5 times more likely to develop dementia than those whose levels increased or stayed the same.
Both cell and animal studies have suggested that high cholesterol contributes to Alzheimer's disease, the researchers noted, but they stressed that the relationship between cholesterol and dementia may vary over a lifetime.
"Our findings highlight how risk factors can change over the course of a person's life span," said Michelle M. Mielke, an assistant professor of psychiatry at Hopkins and lead author of the study, which was published online Nov. 10 in the journal Neurology.
"My biggest worry is that people will look at these results and decide that cholesterol doesn't matter, but that's not what we're saying," Mielke added. "We know that high cholesterol is a very strong risk factor for cardiovascular disease and still needs to be treated with diet, exercise and possibly medication."
Mielke added that it was unclear why a decline in cholesterol levels in old age was linked to a higher risk of dementia, but said it might be an early part of the disease process. "As people start to develop symptoms, they often forget to eat and start losing weight, and that may be why their cholesterol goes down."
For the study, Mielke and her colleagues examined data from the Prospective Population Study of Women, which began in 1968 and consisted of 1,462 Swedish women between the ages of 38 and 60. The women were given follow-up exams at four intervals, the last of which occurred in 2001. In addition to receiving various heart tests, chest X-rays and blood tests, the women were also assessed for dementia at each exam.
In 2001, 161 of the original group had been diagnosed with Alzheimer's or other forms of dementia. While there was no association between dementia and high cholesterol levels at mid-life when including all participants, the researchers did find that the risk of dementia increased from 8.9 percent for those who maintained or had increased cholesterol over the course of the study, while it increased 17.5 percent for people with the greatest decline in cholesterol.
The study teased out findings that echoed other studies: When including the baseline cholesterol levels of only the female participants who survived to old age, "there was a clear trend for high cholesterol to be associated with an increased risk of [Alzheimer's disease]," the researchers reported. Although women with the highest cholesterol levels showed a sixfold increase in risk for Alzheimer's disease compared to those with the lowest, researchers said that trend became statistically insignificant after adjusting for other variables.
Researchers also noted that their research was confined to Swedish women and might not be applicable to men and other ethnicities.
A leading dementia researcher praised the paper's design but had reservations about the findings. "This is a good study because one needs to take a life course trajectory when looking at these kinds of issues," said Lenore J. Launer, chief of the neuroepidemiology section at the National Institute on Aging. "But I think the results are a little bit inconclusive, mainly because of the small sample size."
Launer added that more studies are needed to "better understand how to interpret levels of plasma cholesterol in relation to what's going on in the brain."
In an editorial accompanying the paper, author Mary N. Haan said the findings suggest the need for different prevention strategies, depending on a person's life stage.
"Effective primary prevention of dementia may need to address early and midlife risk factors while, in late life, 'prevention' may necessarily focus on delaying progression of pathology and symptoms," noted Haan, who is a professor of epidemiology at the University of California, San Francisco School of Medicine.
"There a lot of interest right now in trying to prevent dementia, especially Alzheimer's, mainly because none of the treatments work very well," said Haan, who added that one important take-home message for middle-aged and younger people who want to reduce their risk of dementia is to focus on other known risk factors.
"For example, there's a relatively strong and consistent set of evidence linking hypertension with late-life dementia," she said. "So if someone is 45 or 50, and hasn't been screened for hypertension in a while, it's a good idea to do so."
For more on cholesterol, diet and Alzheimer's disease, visit the Alzheimer's Association.