"Most Alzheimer's research has been devoted to factors such as education, heart and blood risk factors, head trauma, family history and genetics," said study author Lena Johannsson, of the University of Gothenburg, Sweden.
    
"Personality may influence the individual's risk for dementia through its effect on behaviour, lifestyle or reactions to stress," Johannsson said.
    
For the study, 800 women with an average age of 46 were followed for 38 years and given personality tests that looked at their level of neuroticism and extroversion or introversion, along with memory tests. Of those, 19 percent developed dementia.
    
Neuroticism involves being easily distressed and personality traits such as worrying, jealousy or moodiness.

People who are neurotic are more likely to express anger, guilt, envy, anxiety or depression.
    
Introversion is described as shyness and reserve and extroversion is associated with being outgoing.    

The women were also asked if they had experienced any period of stress that lasted one month or longer in their work, health, or family situation.
    
Stress referred to feelings of irritability, tension, nervousness, fear, anxiety or sleep disturbances. Responses were categorized as zero to five, with zero representing never experiencing any period of stress, to five, experiencing constant stress during the last five years.
    
Women who chose responses from 3 and 5 were considered to have distress.
    
The study found that women who scored highest on the tests for neuroticism had double the risk of developing dementia compared to those who scored lowest on the tests.

However, the link depended on long-standing stress. Being either withdrawn or outgoing did not appear to raise dementia risk alone, however, women who were both easily distressed and withdrawn had the highest risk of Alzheimer's disease in the study.
    
A total of 16 of the 63 women, or 25 percent, who were easily distressed and withdrawn developed Alzheimer's disease, compared to eight out of the 64 people, or 13 percent, of those who were not easily distressed and were outgoing.
    
The study was published in Neurology, the medical journal of the American Academy of Neurology.

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