Obese people tend to show shrinkage in their brain tissue during middle age – especially if extra kilos are concentrated in the tummy, a new study suggests.
The study, of over 9 600 UK adults, found that those who were obese usually had a lower volume of gray matter in the brain than their normal-weight counterparts. Gray matter contains most of the nerve cells in the brain – while the white matter contains the fibers that connect different parts of the brain.
Risk of developing dementia
Past research has linked the shrinking of gray matter to an increase in risk of future dementia.
However, the researchers warned that they are not able to draw firm conclusions from these latest findings.
The study found an association and does not prove that obesity, by itself, causes the gray matter to shrink. And he did not follow long-term people, said researcher Mark Hamer.
"Since we measured the volume of gray matter on one occasion, it is difficult to interpret whether the differences are clinically significant," said Hamer, a professor at the University of Loughborough, in Leicestershire, England.
Numerous studies have examined whether obese adults have a greater risk of developing dementia and arriving at conflicting conclusions. Some found no correlation, while others suggested that extra pounds could increase the risk of dementia or lower it.
But there is a possible explanation for the discrepancies, said Claudia Satizabal, assistant professor of neurology at Boston University.
A long process
People who eventually develop dementia, he explained, may begin to lose weight five to 1
That's why it's important for studies to look at previous indicators of dementia risk, such as brain volume reduction, said Satizabal, who was not involved in the new research.
"This is a good study," he said. "Dementia is a long process, and this suddenly looks like it happens along the way."
The study included 9,652 people aged 55, on average; 19% were obese
In general, obese men and women generally showed a lower gray matter volume on MRI brain scans, compared to subjects with normal weight.
The largest reductions in gray matter were observed in people who carried a large part of their excess weight around the center. Differences emerged in different regions of the brain, including those involved in the regulation of behavior and movement,
An established risk factor
Why does obesity have any relation to the size of the brain? Hamer has indicated a possibility: obesity and related health conditions – such as hypertension and type 2 diabetes – can damage the heart and blood vessels, which can affect the flow of blood to the brain.
His team took into account the study participants had heart disease, diabetes or hypertension and whether they smoked, drank alcohol or practiced regularly. Even then, obesity itself was linked to a lower gray matter volume.
This suggests that there may be other things going on.
Another possibility, according to Satizabal, is that excess fat itself has an impact. Fat tissue releases various hormones and metabolic by-products that can affect brain health, suggests research.
It is still unclear whether obesity, at least in middle age, is a risk factor for dementia. But Satizabal said: "More and more trials are going in that direction".
Hamer emphasized the broader picture: obesity is a risk factor established for a number of other medical conditions. That said, he said, "people should strive to maintain a normal body weight".
The study was published in the online issue of Neurology .