Broader oceans, smaller brains?

NEW YORK (Reuters Health) – Obese people tend to show shrinkage in their brain tissue in middle age – especially if extra pounds are concentrated in the abdomen, a recent study found.

The study, which includes more than 9 600 adults in the United Kingdom, found that people with obesity usually suffer from a decrease in the size of gray matter in the brain compared to their normal weight counterparts. Gray matter contains most neurons in the brain – while white matter contains fibers that bind different parts of the brain.

Risk of developing dementia

Previous research has linked gray matter shrinkage to increased risk of future dementia.

However, the researchers cautioned that they can not draw firm conclusions from these recent findings.

The study found only an association and does not prove obesity, in itself, causes gray matter shrinkage.

“Since we measured gray matter on one occasion, it is difficult to explain whether the differences are clinically significant,” said Hammer, a professor at Loughborough University in Leicestershire, England.

A number of studies have looked at whether obese adults are at greater risk of developing dementia and reaching mixed conclusions. Some found no association, while others suggested that excess weight may increase or decrease the risk of dementia.

But there is a possible explanation for the contradictions, says Claudia Satizabal, assistant professor of neuroscience at Boston University.

Long process

She explained that people who develop dementia in the end can begin to lose weight from five to ten years before symptoms become apparent. This can disturb any relationship between the risk of obesity and dementia.


That is why it is important for studies to look at previous indicators of risk of dementia, such as brain shrinkage, said Satizapal, who was not involved in the new research.

“This is a beautiful study,” she said. “Dementia is a long process, and this is seen as a feature that occurs along the way.”

The study included 9 652 persons, aged 55 years on average; 19% were obese.

Overall, obese men and women generally showed less gray matter in MRI scans than normal weight participants.


The largest reductions in gray matter were seen in people who carried too much weight around the center. The differences appeared in several areas of the brain, including those involved in regulating behavior and movement, the researchers said.

An existing risk factor

Why does obesity have anything to do with brain size? Hammer pointed to one possibility: Obesity and associated health conditions – such as high blood pressure and type 2 diabetes – can damage the cardiovascular system, which may affect blood flow to the brain.

His team provided whether participants in the study had heart disease, diabetes or high blood pressure and whether they smoked, drank alcohol or practiced regular exercise. Until then, obesity itself was associated with the size of the least gray matter.

This indicates the possibility of other things happening.

The other possibility is that excess fat itself has an effect. Research suggests that fatty tissue releases many hormones and metabolic by-products that may affect brain health.

It is not yet clear whether obesity, at least in middle age, is a risk factor for dementia. But “more and more evidence is going in that direction.”

Hammer pointed to the bigger picture – that obesity is a risk factor for a range of other medical conditions. Given this, he said: “People should seek to maintain a normal body weight.”

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