People who are prone to negative emotions, such as anxiety and anger, may be more vulnerable to the gradual mental decline that can come with age, a study published Monday finds.

The results, reported in the journal Neurology, suggest that chronic distress throughout life may in later years contribute to mild cognitive impairment -- persistent memory difficulties, such as forgetting people's names or misplacing items, which can evolve into advanced dementia.

It's estimated that at least 15 percent of older adults have mild cognitive impairment, many of whom will go on to develop Alzheimer's disease. Experts are still trying to understand exactly why some people develop mild impairment while others don't.

In one recent study, researchers at Rush University Medical Center in Chicago found that older adults who were prone to chronic emotional distress had a higher dementia risk than their less-distressed peers. In the current study, the same group found this was also the case for milder impairment.

Of 1,256 older men and women who were free of mental impairment at the study's outset, those who were distress-prone were about 40 percent more likely to become mildly impaired over the next 12 years.

The findings suggest that chronic distress does not just "speed along" the progression of Alzheimer's disease, but may make people more vulnerable to developing the earliest stages of cognitive impairment, said Dr. Robert S. Wilson, the study's lead author.

This is important, he told Reuters Health, because understanding the risk factors for mild cognitive impairment could allow early interventions to stave off Alzheimer's disease.

People's chronic distress levels can be estimated fairly easily, according to Wilson. For their study, he and his colleagues gauged participants' tendency toward negative emotions using a standard measure of "neuroticism." The measure asks people the level to which they agree with statements like "I am not a worrier," and "I often get angry at the way people treat me."

Because personality traits, including neuroticism, are believed to be largely stable throughout life, a high score on the neuroticism scale is considered an indicator of how much distress a person has suffered over the years.

It's not certain why distress-prone people might be more vulnerable to cognitive decline and dementia. But animal studies have shown that living under stressful conditions can cause changes in the brain that affect learning and memory, Wilson and his colleagues note.

What's more, animal research also suggests that there are ways to lessen the effects of distress on the brain, including antidepressants and exercise, Wilson said.

Whether this is true in people is unknown. More research, Wilson said, is needed to understand how chronic distress affects the human brain.