People who are overweight or obese during middle age have brains with much less white matter than people of the same age at a healthy weight, says study researcher Lisa Ronan, PhD, at the University of Cambridge in the U.K.
White matter tissue helps the brain’s different areas communicate with each other. Loss of it has been linked with declines in thinking skills.
However, in this study, the researchers did not see a difference in thinking skills between healthy weight and overweight people, despite the white matter differences seen on scans of the brain -- a finding that Ronan says surprised her.
Other studies have found a link between obesity and a decline in thinking skills, as well as getting Alzheimer’s disease at an earlier age. Although Ronan didn’t see the same link in her study, experts say losing white matter is not good.
''The white matter of the brain is thought to be the first to go with dementia," says Mike Henne, PhD, a spokesman for the American Federation for Aging Research. Loss of white matter is generally associated with “foggy-mindedness," he says.
White matter declines with age, usually beginning in the late 30s, so holding on to as much as you can is desirable.
"If you lose white matter, the [brain's] neurons are not as capable of communicating with each other," says Henne, assistant professor of cell biology at the University of Texas Southwestern Medical Center.
The Link Between Obesity, White Matter Decline
The U.K. researchers took brain scans of people about 40 years old to measure the impact of weight on brain structure and the amount of white matter. Of the 473 men and women evaluated, 246 were healthy weight, 150 overweight, and 77 obese. The men and women took a standard test similar to an IQ test to measure their thinking skills.
Researchers do not understand exactly how extra weight may affect the brain’s white matter or what having less of it in middle age may mean, Ronan says.
Some experts believe that white matter cells may become more sensitive to inflammation in middle age. "One possibility, and the researchers talk about that [in the report], is that when you are obese your fat cells are producing more inflammatory agents and your white matter is more sensitive to it," Henne says. "That is a leading theory in the field."
Ronan says a limitation of the study is that she evaluated people at only one point in time.
While the new study did not link being overweight with an earlier onset of thinking problems and dementia, it brings much needed research attention to an area often neglected by researchers, Henne says.
The study’s researchers said more researchers will need to study the brains of people over longer periods of time to help them better understand how weight impacts brain health. But the study supports the idea that too much weight “confers a significant risk” to thinking skills.