In addition to reduced incidence of Alzheimer's, people who exhibit a strong behavioral pattern of self-discipline, who control their impulses and are goal-oriented and responsible, may also experience a slower rate of cognitive decline and a lower risk of mild cognitive impairment, the study suggests.

Important for Overall Health

Conscientiousness has been associated with a wide range of mental and physical disorders, disability and death, suggesting it may be important for maintaining overall health, the researchers note.

There are a number of possible explanations for how conscientiousness might protect against Alzheimer's disease. Conscientious people may be more likely to succeed in their educational and professional objectives. They may be more resilient and have better coping strategies.

"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," say the authors.

89 Percent Lower Risk

Almost 1,000 older Catholic nuns, priests and brothers took part in the study. None had dementia when it began in 1994. Their evaluations included medical histories, neurologic examinations and cognitive testing.

A 12-item inventory was employed to determine their level of conscientiousness. Participants rated agreement with each item -- for example, "I am a productive person who always gets the job done" --on a scale of one to five.

Scores ranged from zero to 48, with higher scores indicating more conscientious individuals. The researchers conducted follow-up examinations annually through 2006, with an average of 7.9 evaluations per person.

The participants had an average conscientiousness score of 34 out of 48. Through a maximum of 12 years of follow-up, 176 individuals developed Alzheimer's disease.

Those who had conscientiousness scores in the 90th percentile (40 points) or higher had an 89 percent lower risk of developing Alzheimer's disease than those whose scores ranked in the 10th percentile (28 points) or lower. Controlling for known Alzheimer's disease risk factors did not substantially change these results..

Not Linked With Pathologic Hallmarks

The researchers also analyzed results from brain autopsies of 324 participants who died during the study. Conscientiousness was not linked to any of the hallmark signs of Alzheimer's disease, including brain plaques and tangles, in those patients.

However, conscientiousness did appear to modify the association of such brain changes with an individual's cognitive abilities before death.

"Level of conscientiousness is associated with incidence of mild cognitive impairment and Alzheimer's disease, but not with the pathologic hallmarks of these conditions," the researchers conclude.

"Understanding the mechanisms linking conscientiousness to maintenance of cognition in old age may suggest novel strategies for delaying the symptoms of Alzheimer's disease."