CHICAGO, Oct 1 (Reuters) - People who lead a good clean life -- those who are conscientious, self-disciplined and scrupulous -- appear to be less likely to develop Alzheimer's disease, U.S. researchers said on Monday.

The finding is the latest from a long-running study of nearly 1,000 Catholic nuns, priests and brothers by Robert Wilson of Rush University Medical Center in Chicago. The study appeared in the Archives of General Psychiatry.

Wilson and colleagues defined conscientiousness in the study as people who control their impulses and are goal-directed. These people are often considered dependable.

People in Wilson's study did not have dementia when the study started in 1994.

The researchers asked the volunteers to rank themselves on a five-point scale according to a 12-item inventory, with questions such as "I am a productive person who always gets the job done." From this, they derived a conscientiousness score, based on a scale of 0 to 48. The average score was 34.

They were also given various medical and neurological exams, including cognitive testing. Follow-up tests were done each year through 2006. A total of 176 people developed Alzheimer's disease during the study.

People who were highly conscientious -- those in the 90th percentile with scores of 40 or higher, had an 89 percent lower risk of developing Alzheimer's disease than those who ranked in the 10th percentile, with a score of 28 or lower.

The researchers also found that conscientiousness was linked with a slower rate of cognitive decline and a lower risk of mild cognitive impairment, a risk factor for Alzheimer's disease.

Why conscientious people are less prone to Alzheimer's is not clear, but Wilson and colleagues suggested it may be because conscientious people tend to be more resilient, making them better able to cope with difficulties.

Such people also tend to have a fair measure of success in school and work, they said.

"These factors might lessen the adverse consequences of negative life events and chronic psychological distress, which have been associated with risk of dementia in old age," the authors wrote.

According to the World Health Organization, about 18 million people worldwide have Alzheimer's disease, a brain-wasting condition marked by memory loss and confusion that becomes so severe patients lose the ability to care for themselves.

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