Stress — over work, money, family, or illness — is fact of modern living, but new research shows that chronically high stress levels boost the risk of developing dementia.

The findings, by an international research team from Ireland and India, indicate chronic stress shrinks the region of the brain known as the hippocampus — the seat of learning and memory. The team also found that even a brief period of stress — as few as several days — can cause the hippocampus to start shrinking.

"Until now, no one actually knew the evolution of these changes. Does the hippocampus shrink before or after memory loss? Or do the two happen hand-in-hand?" asks Sumantra Chattarji, one of the main investigators in the study.

Chattarji and colleagues from the National Centre for Biological Sciences in Bangalore and Trinity College, Dublin, tracked laboratory rats’ reactions to two hours of stressful experiences over 10 days.

The researchers found the rodents respond to stress much as humans do — they develop anxiety-related behaviors and their ability to form memories are affected. MRI scans of the rats' brains also found “striking results” — after just three days of stress, the hippocampus of every stressed rat had shrunk.

"It was a totally unexpected result. Normally structural changes are seen in the brain after a long time —say 10 to 20 days. Three days doesn't even count as chronic stress," says Chattarji.

The findings, published in the journal Scientific Reports, could have significant implications for people, Chattarji says.