Obesity joins a growing list of lifestyle risk factors for Alzheimer's -- high cholesterol, high blood pressure, and diabetes.
This newest study is "probably the first to look at obesity as an independent risk factor for Alzheimer's disease... and the first to follow patients for a long period of time," which gives considerable credibility to the findings, says lead researcher Deborah Gustafson, PhD, a professor in family and community medicine at the Medical College of Wisconsin in Milwaukee.
Her study, conducted in Sweden, appears in this week's issue of Archives of Internal Medicine.
In their study, Gustafson and her Swedish colleagues tracked 392 men and women -- all age 70 at the study's beginning -- for 18 years. Each had a battery of exams every five years or so, including brain scans to identify onset of dementia. The findings:
- Women who developed Alzheimer's disease between the ages of 79 and 88 were significantly more likely to have been overweight at ages 70, 75, and 79, reports Gustafson.
- Women with Alzheimer's had a body mass index (BMI) about four units higher than women without dementia, she adds.
BMI is a measure of body fat, taking into account a person's height and weight. A BMI between 19 and 25 is considered normal, over 25 is overweight, and 30 or higher is obese. An example: A woman who is 5 feet 4 inches tall, weighing 170 pounds, would have a BMI of 29.
- In this study, a woman's risk of Alzheimer's increased by 36% with each notch over a BMI of 25, says Gustafson.
- Women with a BMI of 25 -- what's considered a moderate, healthy weight -- were less likely to have dementia. "That's not super-skinny, it's kind of borderline between healthy and overweight," says Gustafson.
Men in this study did not have such a high risk of Alzheimer's disease. "Very few men lived the full 18 years of the study, and very few of those were demented," she explains. However, because the number of men was so small, the results may be skewed, she adds.
What's Going On?
"Body fat has a profound effect on blood vessels -- it causes stiffening of blood vessels throughout the body, including heart and brain," says Gustafson. However, obesity could also trigger an as-yet-unknown metabolic syndrome that leads to Alzheimer's, she says.
Gustafson's study is "consistent with emerging evidence," says Lindsay Farrer, PhD, chief of genetics and professor of medical neurology, genetics, and genomics, and epidemiology at Boston University School of Medicine.
Indeed, evidence suggests that risk factors for cardiovascular disease and Alzheimer's are similar, but no one is sure why. "The smoking gun has yet to come out of the closet," he tells WebMD.
Should people take weight-reducing drugs to prevent Alzheimer's? "There are lots of reasons to lose weight -- it prevents diabetes, heart disease, high blood pressure, cancer. But taking one of those drugs to prevent Alzheimer's should not be the main reason," Farrer says.
"Being leaner puts you at lower risk for those other diseases," says Farrer. "But what's protecting you -- is it the fact that you're leaner, or that you don't have diabetes? Diabetes, after all, is a risk factor for Alzheimer's. There are a lot of unmeasured variables."
Genetics Research Ongoing
Since 1991, Farrer has led a large, multi-center, multi-ethnic study tracking 1,000 pairs of siblings -- all between ages 60 and 85. The siblings were chosen for the study if one has Alzheimer's, but the other does not.
As in Gustafson's study, each person has a battery of tests every few years, including brain scans and genetic testing. "We're looking at 100-plus genes that are suspected or known to have a role in [blood vessel changes]," says Farrer.
"Gene therapy is not necessarily tinkering with the genetic makeup," he tells WebMD. "Here, gene therapy means using genetics to understand more rational approaches -- lifestyle changes -- that accentuate or lessen the effects of these genes."