This is a large percentage of the population, said Thompson, who is also a member of UCLA's Brain Research Institute and the UCLA Laboratory of Neuro Imaging.

"This is a shocking finding. Any loss of brain tissue puts you at greater risk for functional decline," he said. "The risk gene divides the world into two camps • those who have the FTO allele and those who don't."

But the news is not necessarily completely negative, Thompson said, because "carriers of the risk gene can exercise and eat healthily to resist both obesity and brain decline."

Thompson sees both a public health message and a science message in this finding.

"Half of the world carries this dangerous gene. But a healthy lifestyle will counteract the risk of brain loss, whether you carry the gene or not. So it's vital to boost your brain health by being physically active and eating a balanced diet," he said.

And from a scientific standpoint, he said, "the gene discovery will help to develop and fine tune the anti-dementia drugs being developed to combat brain aging."

Source: University of California - Los Angeles