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updated 10/1/2014 4:46:58 PM ET 2014-10-01T20:46:58

Women who feel anxious, moody and distressed for significant amounts of time during middle age may be at an increased risk of developing Alzheimer's disease later in life, a new study suggests.

In the study, researchers followed 800 women over 38 years. At the study's start, their  average age was 46. The researchers assessed the women's levels of distress and neuroticism, which is a personality trait that psychologists describe as the tendency to feel negative emotions when you are threatened or frustrated. The researchers also examined the women's memory abilities, and looked at how extroverted or introverted they were.

During the study, 153 women developed some type of dementia, including 104 who developed Alzheimer's disease. The researchers found that the women with the highest levels of neuroticism who also experienced long-standing distress were twice as likely to develop Alzheimer's disease as the women with the lowest levels of neuroticism.

"We … saw that persons with a high degree of neuroticism, combined with a low degree of extraversion, had the highest risk of AD," study author Lena Johansson of the University of Gothenburg in Sweden, told Live Science. [ 10 Ways to Keep Your Mind Sharp ]

However, the women's levels of neuroticism alone did not have a significant effect on their risk of Alzheimer's, unless their neuroticism was also accompanied by long-standing distress, according to the study.

But the link the researchers found was an association, not a cause-and-effect relationship between neuroticism and Alzheimer's.

"It is possible that neuroticism makes the individual more vulnerable to stressors and distress, which leads to later development of dementia," the researchers wrote in the study, published today (Oct. 1) in the journal Neurology.

To measure the women's level of distress, at five points during the study, the investigators asked them if they had experienced any period of stress in the last five years about their work, health or family situation that lasted at least a month. The women rated their stress on a scale from zero to five, and the researchers considered women who chose responses between three and five to have experienced distress.

There are several possible ways that neuroticism and Alzheimer's disease may be linked, the researchers wrote. It could be that people with less neurotic personalities may have different lifestyles, compared with those who have higher levels of neuroticism, and those lifestyles may affect their health in ways that affect their risk of Alzheimer’s.

But studies have also shown that both neuroticism and stress are associated with certain changes in the brain, which in turn may affect learning, cognition and memory, they wrote.

Previous research has found a link between a lower risk of Alzheimer's disease and lower neuroticism, the researchers wrote. Future studies should examine the exact mechanisms behind the link between neuroticism and Alzheimer's disease, Johansson said.

"It remains to be seen whether neuroticism could be modified," for instance through medical treatment or lifestyle changes, she said.

"Taken together, these findings are consistent with a broader truth that people who are more exposed (or more vulnerable) to the vicissitudes of life may also be less likely to ‘age well,’ whether this is measured by mortality, cardiovascular disease, AD [Alzheimer’s disease], or other aging-related outcomes," Dr. Robert Stewart of King’s College London, who was not involved in the study, wrote in a related editorial.

Follow Agata Blaszczak-Boxe on Twitter. Follow LiveScience@livescience, Facebook  &Google+.Originally published onLive Science.

© 2012 LiveScience.com. All rights reserved.

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