A 38-year study has found that neurotic women have a higher risk of developing Alzheimer's disease in later life, researchers say.

Anxious, jealous, moody or distressed middle aged women may be putting themselves at risk of developing Alzheimer's disease, according to a 38-year long study.

The claim, which appears in Neurology online, comes after scientists used personality and memory tests to track the health and welfare of 800 women who had an average age of 46. They found that 19 per cent of those women developed dementia in later life.

The tests also looked at their levels of neuroticism, whether they appeared to be shy and reserved plus also if they were outgoing characters.

Neurology online is the medical journal of the American Academy of Neurology. Study author Lena Johannsson of the University of Gothenburg, Sweden said: "Most Alzheimer's research has been devoted to factors such as education, heart and blood risk factors, head trauma, family history and genetics.

"Personality may influence the individual's risk for dementia through its effect on behaviour, lifestyle or reactions to stress."

Neuroticism involves being easily distressed and can be linked to worrying, jealousy or moodiness. People who are neurotic are more likely to express anger, guilt, envy, anxiety or depression. The study also looked at women who appeared to be shy and reserved plus those who seemed to be outgoing.

The women were asked if their work, health or family situation had left them feeling stressed for at least a month. Stress might be spotted by feeling irritable, tense, nervous, fearful, anxious and not being able to sleep properly.

Responses were ranked from zero, where the women said they never felt stressed, to five, where they said they had constantly experienced stress in the last five years. Women who chose responses from three and five were considered to have distress.

Those women with the highest scores on the tests for neuroticism had double the risk of developing dementia compared to those who scored lowest on the tests, according to the study.

The scientists point out that the link depends on long-standing stress.

Being either withdrawn or outgoing did not appear to raise dementia risk alone, but women who were both easily distressed and withdrawn had the highest risk of Alzheimer's disease in the study.

It was found that 16 of the 63 women who were easily distressed and withdrawn developed Alzheimer's disease. This compared to eight out of the 64 people who were not easily distressed and were outgoing.

Dr Simon Ridley, head of research at Alzheimer's Research UK, said: "Observational studies like this can be important for picking out health trends but this type of research is not able to tell us about cause and effect.

"This long-term study adds to existing evidence linking stress to an increased risk of dementia, but more research is needed to understand the underlying reasons behind this link, as well as the impact of some of the personality traits highlighted here. There are many reasons for acting to reduce people's stress levels but controlled trials would be needed to know whether alleviating this type of stress could help prevent Alzheimer's in later life.

Copyright AAP 2014