A study has linked obesity with a decrease in brain tissue which could negatively affect cognition and function, south Australian researchers report.

Professor Elina Hypponen

The study, published in Neurobiology of Ageing, wasn’t able to establish a link between increased body fat and dementia, although it did find an associated atrophy of dark brain tissue known as grey matter, which also marks progression of the disease.

The study examined 336,000 records from the UK Biobank.

Researchers looked at three different types of obesity – unfavourable, neutral and favourable – to see whether some groups were at more risk than others.

“We found that people with higher levels of obesity, especially those with metabolically unfavourable subtypes had much lower levels of grey brain matter, indicating that these people may have compromised brain function which needed further investigation,” lead researcher Dr Anwar Mulugeta from the Univeristy of South Australia said.

Metabolic problems

In the 37-73 age group grey matter decreased by 0.3 per cent for every extra 3 kg of weight for person of average height ( about 173 cm).

The study suggests that inflammation and metabolic problems associated with obesity, such as high cholesterol and high blood pressure,  could play a role in brain atrophy, director of the Australian Centre for Precision Health and senior principal research fellow at SAHMRI Professor Elina Hypponen says.

“In our study we found evidence for a harmful effect of greater adiposity on brain volume. However, our data also shows, that not all types of adiposity are likely to have similar effects,” she told Community Care Review.

“Our study suggests that brain volume may be negatively affected particularly by excess adiposity that comes together with the common metabolic abnormalities associated with obesity, that is low grade inflammation, high lipids and high blood sugar. 

“In contrast, excess adiposity which does not come with inflammation and is associated with normal blood sugar was associated with larger brain volumes.”

She says the mechanisms behind this isn’t well known, although some of the secretions from fat tissue that cause inflammation are know to cross over into the brain.

“These may  … cause neuroinflammation and contribute to brain atrophy,” she said.

 Professor Hypponen says it’s too much of a stretch at this stage to say that obesity can increase the risk of dementia.

However the findings fit with the notion that “what is good for your heart is good for your brain,” she says.

“Our results suggest that efforts to control for metabolic abnormalities which are associated with obesity, may be beneficial with respect to minimising the adverse effects of excess adiposity on the brain.”

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