December 23, 2009
Being overweight or obese leads to brain shrinkage in old age and, researchers say, an increased risk of Alzheimer's disease. Those are the findings from scientists at the University of California, Los Angeles, and the University of Pittsburgh.
"The brains of obese people looked 16 years older than the brains of those who were lean, and in overweight people looked 8 years older," said Paul Thompson, a brain researcher at U.C.L.A. who was the study's senior author. "That's a big loss of tissue, and it depletes your cognitive reserves, putting you at much greater risk of Alzheimer's and other diseases that attack the brain."
Using high-resolution brain scans, the researchers found that the brains of those who were overweight or obese shrank by 4 to 8 percent compared to peers who were at a healthy weight. Brain areas that were particularly affected were the frontal lobes and the hippocampus, areas critical for thinking and memory.
Although none of the 94 seniors, ages 70 and older, who participated in the study showed symptoms of Alzheimer's or serious memory loss, the researchers believe that they would be at increased risk of the disease as the years wore on. That's because a shrunken brain has fewer brain cells and fewer robust connections between cells, making it less resilient to the ravages of a brain ailment like Alzheimer's than a larger, healthy brain.
"But you can greatly reduce your risk for Alzheimer's if you can eat healthily and keep your weight under control," Dr. Thompson said.
Overweight is usually defined as a body mass index, or BMI, of 25 to 30, while being obese is defined as a BMI of 30 and higher. For someone who is 5-foot-9-inches, for example, a normal weight would be 125 to 168 pounds; overweight would be 169 to 202 pounds; and obese would be 203 pounds or more, according to BMI measurements.
Excess pounds have been linked to increased risks of heart disease and diabetes as well, both of which increase Alzheimer's risk too, perhaps through damaging blood vessels. Scientists also speculate that fat cells may produce harmful chemicals that promote inflammation, which may damage the brain. People who are overweight may also tend to have diets low in "good" fats, such as those found in fish, and to get less exercise than those who are of normal weight.
Age remains the most important risk factor for Alzheimer's: The older you are, the more likely you are to develop the disease. Smoking, high blood pressure, years of schooling, and genetic factors may also contribute to risk, other research has shown. More research is needed on the effects of body weight and other risk factors for Alzheimer's disease.
Nevertheless, with more and more Americans both young and old becoming obese, it is vital that people maintain healthy lifestyles that may also help maintain the brain. Learn more about risk factors for Alzheimer's disease at www.ALZinfo.org, The Alzheimer's Information Site.
Source: Cyrus A. Raji, April J. Ho, Neelroop N. Parikshak, et al: "Brain Structure and Obesity." Human Brain Mapping, August, 2009.