As the Waistline Expands, the Brain Shrinks!
BRAIN regions key to cognition are smaller in older people who are obese compared with their leaner peers, making their brains look up to 16 years older than their true age. As brain shrinkage is linked to dementia, this adds weight to the suspicion that piling on the pounds may up a person's risk of the brain condition.
Previous studies suggested that obesity in middle age increases the risk of dementia decades later, which is accompanied by increased brain shrinkage compared with leaner people. Now brain scans of older people have revealed the areas that are hardest hit, as well as the full extent of brain size differences between obese people and those of average weight.
From brain scans initially carried out for a different study, Paul Thompson from the University of California in Los Angeles and colleagues selected 94 from people in their 70s who were still "cognitively normal" five years after the scan. This was to exclude people with disorders that might have confused the results. The researchers then transformed these scans into detailed three-dimensional maps.
People with higher body mass indexes had smaller brains on average, with the frontal and temporal lobes - important for planning and memory, respectively - particularly affected (Human Brain Mapping, DOI: 10.1002/hbm.20870). While no one knows whether these people are more likely to develop dementia, a smaller brain is indicative of destructive processes that can develop into dementia.
The team also found that the brains of the 51 overweight people were 6 per cent smaller than those of their normal-weight counterparts, on average, and those of the 14 obese people were 8 per cent smaller. "The brains of overweight people looked eight years older than the brains of those who were lean, and 16 years older in obese people," says Thompson.