CHICAGO - People who are often stressed out or depressed are far more likely to develop memory problems than those with sunnier dispositions, US researchers said on Monday in a finding that sheds light on early predictors of Alzheimer's disease.

They said those who most often are anxious or depressed were 40 times more likely to develop mild cognitive impairment, a form of memory loss that is often a transitional stage between normal aging and dementia.

"Not only are these individuals losing cognition, but they are showing many of the changes in the brain that are associated with Alzheimer's disease," said Robert Wilson of Rush University Medical Center in Chicago.

In prior studies, Wilson found that people who are more prone to distress are more likely to develop Alzheimer's disease than their more carefree counterparts.

"We now see that chronic distress is related to the first clinical manifestation of Alzheimer's disease," he said in a telephone interview.

People with mild cognitive impairment have some trouble remembering things, but they do not have significant disability. Not all people with this problem develop Alzheimer's disease, a much more serious impairment, but about 10 to 15 percent do, according to the Alzheimer's Society.

Wilson and colleagues analyzed data from two large studies involving 1,256 older people who started the studies with no memory problems.

After up to 12 years of follow up, 482 people in the study developed mild cognitive impairment. Participants were rated on how prone they are to worry and depression.

"What we're measuring is a personality trait that we all have to greater or lesser degree. We all experience anxiety and periodic depression. This trait helps identify people for whom that is more characteristic than others," said Wilson, whose study appears in this week's issue of the journal Neurology.

"This isn't a measure of stress, but of the response to stress," he said.

The latest research suggests that chronic stress may harm parts of the brain responsible for responding to stress - an area that is also associated with memory, he said.

"The bigger impact on public health will depend on us understanding the neurobiological basis for this," he said.

That is not yet clear, but the research might lead to early treatments, such as promoting exercise to reduce stress or drug therapy for depression.

"It could open up new avenues for strategies to delay the symptoms of this disease," he said.