The brains of overweight middle-aged people appear 10 years older than those of slim people of the same age, according to a new study in the journal Neurobiology of Aging. The research revealed that obese individuals who were 50 years old tended to have lost the same amount of white matter – which connects brain areas together – as 60-year-olds with a lean figure.
It has long been known that as people age, the white matter in their brain begins to shrink. Since white matter contains the connecting branches – known as axons – of neurons, it is sometimes thought of as a kind of cerebral superhighway, along which electrical impulses travel as the various regions of the brain communicate with one another.
Researchers recruited 527 volunteers aged 20 to 87, each of whom was classified as either “lean” or “overweight”, depending on their body mass. After scanning the brains of all participants, the study authors found that from middle-age onwards, the brains of overweight people tended to shrink more than those in the lean group.
On average, overweight brains displayed a degree of shrinkage comparable to lean brains 10 years their senior. Study co-author Lisa Ronan explained in a statement that “it isn’t clear why people who are overweight have a greater reduction in the amount of white matter,” adding that “we can only speculate on whether obesity might in some way cause these changes or whether obesity is a consequence of brain changes.”
This image shows the white matter (in yellow) of a lean 56-year-old (left) and an overweight 50-year-old (right). Lisa Ronan
Although the researchers are not yet sure what causes this effect, they theorize that it may have something to do with inflammation. As we age, we experience increasing levels of oxidative stress, which refers to the production of certain molecules that cause damage to body tissues. Previous work has shown that this often leads to inflammation, which in turn causes the loss of white matter.
Since the build-up of fatty tissue causes the release of inflammatory compounds called cytokines, as well as inflammatory hormones like leptin, the researchers suspect that this may at least partially explain why obesity causes such extreme neurodegradation.
Fortunately, despite this loss of white matter, overweight individuals did not appear to have lost any cognitive capabilities, and performed just as well on IQ tests as lean people of the same age.
The researchers are also at a loss as to why this effect only seems to kick in from middle age onwards, and believe that certain biological changes that occur during this phase of life may somehow leave the brain more vulnerable to the effects of weight gain. More work will be needed to clarify this point, and also to determine if losing weight can reverse these effects.