(HealthDay News) -- Obesity and its common companions -- diabetes and heart disease -- can work together to speed dementia and other brain ills, a series of new studies shows.
One expert thinks these papers, published in the March issue of Neurology, deliver a key message, namely that people can take steps to reduce their risk of developing dementia and Alzheimer's disease. People think about lifestyle factors in preventing heart disease, he says, but not always when it comes to losing mental abilities.
"This is an important message," said Dr. Ronald C. Petersen, chairman of the Medical and Scientific Advisory Council of the Alzheimer's Association and director of the Alzheimer's Disease Research Center at the Mayo Clinic. "Development of cognitive decline need not be a passive process."
"We are not all just sitting here and aging, and sooner or later it's going to hit us," said Petersen, who was not involved in the studies. "In fact, there may be some modifiable lifestyle factors that may influence our risk of developing cognitive impairment and Alzheimer's disease down the road."
In one report, Dr. Kristine Yaffe, a professor at the University of California, San Francisco, and director of the Memory Disorders Clinic at the San Francisco Veterans Affairs Medical Center, found that among older women, obesity, high blood pressure and a low level of HDL, the "good" cholesterol -- collectively labeled metabolic syndrome -- were each associated with a 23 percent increase in risk for cognitive impairment.
Yaffe's research team collected data on 4,895 women who averaged 66 years old and who had no cognitive impairment at the start of the study. Among the 497 women with metabolic syndrome, about 7 percent developed cognitive impairment, compared with 4 percent of the women without the condition.
"As the obesity and sedentary lifestyle epidemic escalates throughout the world, identification of the role of these modifiable behaviors in increasing risk for development of deleterious outcomes, such as cognitive impairment, is critical," the authors concluded.
In a second study, Yaffe's group found a cognitive risk for obese men, too. For that study, the researchers collected data on 3,054 older men and women.
Comparing people's scores on tests given at the beginning of the study and again three, five and eight years later, the researchers discovered that obese men were more likely to show signs of cognitive decline. However, there was no correlation between obesity and cognitive decline among women, the study reported.
A third report found a different trend. In that study, Annette L. Fitzpatrick, a research associate professor of epidemiology at the University of Washington, in Seattle, and colleagues found that obesity in middle age increased the risk for dementia. However, after age 65, underweight people rather than obese people were at higher risk for dementia.
In fact, obesity appeared to have a protective effect, the researchers noted.
They had collected data on 2,798 men and women who averaged 75 years old and who did not have dementia at the start of the study. During more than five years of follow-up, 480 people developed dementia; in 245 people, it was determined to be Alzheimer's disease.
"The greatest dementia risk was found in underweight individuals at older ages," the researchers concluded. "These findings suggest the predictive ability of BMI [body-mass index] changes across time." They added that the findings "help explain the 'obesity paradox' as differences in dementia risk across time are consistent with physical changes in the trajectory toward disability."
In the fourth report, Elizabeth P. Helzner and colleagues from Columbia University Medical Center in New York City collected data on 156 people diagnosed with Alzheimer's disease at an average age of 83.
They found that people with higher total and LDL, or "bad," cholesterol levels and diabetes had a more rapid cognitive decline after developing Alzheimer's disease.
The study "provides further evidence for the role of vascular risk factors in the course of Alzheimer's disease," the researchers concluded. "Prevention or treatment of these conditions can potentially slow the course of Alzheimer's disease."
More and more data are showing the connection between lifestyle and cognitive decline, Petersen stressed. "This series of articles underlines that," he said.
And people need to improve these lifestyle factors in middle age, he said.
"People should start paying attention now, regardless of your age or stage in life," he said. "It may be when you are in midlife, when you are in your 40s or 50s, what you do then with respect to your lifestyle -- your diet, your weight, your activity level -- may have a bigger impact on what's going to happen to you at age 70 and beyond than if you wait until you start getting a little forgetful or a little bit fuzzy."
The U.S. National Institute of Neurological Disorders and Stroke has more on dementia.
SOURCES: Ronald C. Petersen, M.D., Ph.D., chairman, Medical and Scientific Advisory Council, Alzheimer's Association, and director, Alzheimer's Disease Research Center, Mayo Clinic, Rochester, Minn.; March 2009 Archives of Neurology