Excess Weight May Shrink the Brain's White Matter

With commentary by Nicolas Musi, MD, spokesperson for the American Federation for Aging Research and director of the Barshop Institute for Longevity and Aging Studies at the University of Texas Health Science Center at San Antonio.

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Middle-age spread is not only unattractive and a risk factor for developing type 2 diabetes. Those who are overweight or obese at middle age—roughly, age 40—appear to have much less white matter in their brains than people of the same age who are at a healthy weight, according to a new study. The extra weight appears to age their brain a full decade, the researchers found.

White matter is important—it helps the brain's nerve cells (neurons) communicate with each other. White matter begins to decline in the late 30's, so holding onto as much as possible is important to maintain good thinking skills and brain functioning.

"In our study we showed that the white matter of overweight and obese people was reduced more than you would expect for their age," says Konrad Wagstyl, a PhD student and researcher at the University of Cambridge in the U.K. "In middle age where the difference was greatest, obese people had white matter volumes more commonly seen in lean people who were 10 years older."

Wagstyl says they found only a link, or association. "While we can't be certain here that the reduced white matter is the cause or effect of obesity, these findings are in keeping with a huge amount of evidence which suggests that being obese is a health risk on many levels," he says. The researchers looked only at the effects of obesity, not the effects of diabetes, he says. However, many in the obese group did have diabetes, he says.

The research is published in the Neurobiology of Aging.

White Matter Deficit: A Closer Look

The researchers evaluated 473 men and women, ages 20 to 87. They divided them into two groups—lean or normal weight and overweight and obese. They used standard definitions, terming those with a body mass index (BMI) of 18.5 to 24.9 healthy, 25 or higher overweight and 30 and higher obese.

Next, they did brain scans to measure the volume of white matter.  The researchers also tested the thinking skills of the men and women. In other research, white matter decline has been linked with developing Alzheimer's at an early age.

They found the decade differences from middle age on in the overweight and obese compared to the healthy weight men and women. For instance, an overweight person of 40 had a white matter volume that looked like that of a healthy weight person of 50.

Surprisingly, the researchers found no differences in thinking skills between the groups, although they expected to.

Explaining the Weight-Brain Link

The U.K. researchers can't say for sure why the excess weight seems to speed up the decline of white matter, nor what the implications will turn out to be for cognitive skills.

But they speculate that the culprit may be inflammation, which accompanies obesity. Hormones produced by fat tissue could also play a role, they say.

From the study results, the researchers cannot say for sure if it’s the obesity or related factors driving the changes in white matter, agrees Nicolas Musi, MD, a spokesperson for the American Federation for Aging Research and director of the Barshop Institute for Longevity and Aging Studies at the University of Texas Health Science Center at San Antonio. He reviewed the findings. Many factors may explain the decline, he says, including diabetes and insulin resistance, for instance.

As for why the differences became apparent in middle age, Dr. Musi says that simply may be when it becomes more noticeable on brain scans. "I think it's just a progression," he says of the white matter decline, "a linear progression."

Action Plan

It's not known, Wagstyl says, if losing weight could help people hold onto white matter or even reverse the effects. "We are now looking into these questions," he says.  

Dr. Musi advises those who are overweight not only to try to lose the excess but to maintain good blood sugar levels, healthy cholesterol and blood pressure levels. "All these things are important at many levels," Musi says. "One is blood flow to the brain." It helps the brain work well, he says.

Regular exercise can also help blood flow to the brain, and improve functioning, he says.

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