People who easily get stressed out may be more likely to develop memory problems than those who are more laid back, say researchers who tracked early changes linked to Alzheimer's disease.

The team analyzed the results of two studies on more than 1,200 people with no memory problems who were followed for up to 12 years.

Participants who often experienced negative emotions like depression and anxiety were 40 per cent more likely to develop memory loss that may occur before dementia, study author Robert Wilson of Rush University Medical Center in Chicago and his colleagues said.

How people respond to negative emotions and distress tends to stay the same throughout their adult lives, Wilson noted.

"These findings suggest that, over a lifetime, chronic experience of stress affects the area of the brain that governs stress response. Unfortunately, that part of the brain also regulates memory."

Mild cognitive impairment is often considered a transition stage between normal aging and dementia. People with mild cognitive impairment have memory problems but there is no major disability.

Doctors may watch for signs that mild cognitive impairment is worsening toward Alzheimer's, such as if a person starts having trouble concentrating or making decisions as more than one aspect of brain function is affected.

In the study, 482 people developed mild cognitive impairment.

Participants were rated on how prone they were to distress and negative emotions, based on how much people agreed with statements such as "I am not a worrier," or "I often feel tense and jittery."

The study's authors talked about their findings in Tuesday's issue of the journal Neurology.

Researchers do not know how stress responses affect the brain, but it is hoped that studies into stress-relieving approaches like exercise or antidepressants may offer new ways to delay symptoms of Alzheimer's.