Photograph by Rogelio V. Solis, AP

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More than one-third of Americans are obese, with serious consequences for heart health and, new research suggests, cognitive abilities later in life.

Photograph by Rogelio V. Solis, AP

Rise in Weight Linked to Cognitive Decline in Older Adults

Obesity could cause shrinkage in a brain area critical to long-term memory.

An expanding waistline may lead to a shriveled brain, new research suggests.

In a long-term study of people in their early 60s, a brain region called the hippocampus shrank close to 2 percent a year in those who were obese—a rate approaching levels seen in Alzheimer's disease.

In people of normal weight, the hippocampus, which is crucial for processing memories for later retrieval, shrank roughly half as much, according to an eight-year study discussed at a press conference Tuesday at the Society for Neuroscience meeting in Washington, D.C.

Earlier research on weight and the brain focused mostly on the impacts of obesity in middle-aged people, said neuroscientist and study co-author Nicolas Cherbuin of the Australian National University, in Canberra.

But participants in the new study were 60 to 64 years old when the study began, providing evidence of a link between elderly corpulence and declining cognitive powers—sobering news in nations such as the United States where the population is getting both older and fatter.

"People may think, 'Oh, well, I'm in old age, I'm retired, it won't matter.' It does matter," Cherbuin said. "The more obese one is, the more shrinkage there will be."

Larger Waist, Slimmer Hippocampus

Cherbuin and his colleagues used magnetic resonance imaging (MRI) to examine the brains of more than 400 people in their 60s who'd volunteered for a study of aging. At the beginning of the study, obese subjects already had smaller hippocampuses than did subjects who were merely overweight. (A person who stands five feet, nine inches tall is overweight at 169 to 202 pounds and obese at 203 pounds or more, according to the formula used by the U.S. Centers for Disease Control and Prevention.)

That linkage between weight and hippocampus size held even when researchers took into account education, physical activity, and other factors that might have led to differences in hippocampal size.

As if it weren't bad enough that they started out with smaller hippocampuses, the obese subjects lost hippocampal volume more quickly than their slimmer fellows did. The rate of hippocampal shrinkage seen in the fatter participants is likely to lead eventually to memory loss, mood changes, and problems with concentration and decision-making, Cherbuin said.

Double-Whammy Effect

It's not clear why fleshiness of the body would lead to attrition of the brain, but one possible factor is the cocktail of immune-system chemicals that leach from fat cells. More fat cells means higher production of these potent compounds. They have a double-whammy effect on the hippocampus, fostering cell death while also curbing cell birth.

The new results are plausible in light of animal research connecting obesity and loss of cognitive abilities, said University of Pittsburgh neuroscientist Judy Cameron, who was not involved in the research.

The results emphasize the need to get out the word about the connection between obesity and brain declines, she said. More than one-third of U.S. adults are obese, according to the CDC.

Obese, sedentary people are aging without "a lot of neural protection," Cameron said. "By losing weight and exercising more, they would be much more protected against neurodegenerative diseases. It's a message that needs to get out to the public."

Obesity levels are "a time bomb" when it comes to brain health, Cherbuin agreed. "If we don't do [something] now, we're going to pay so much in 20 or 30 years. We just can't let it happen."