Lead author Hui-Xin Wang surveyed 506 individuals over the age of 78, none of whom were suffering from dementia at the onset of the study. One set of survey questions focused on personality, and sorted the participants according to various traits. Some individuals were extraverted and tended to be social and optimistic. Some were prone to distress and tended to be nervous, negative, and more often emotionally unstable. And some participants were more laid-back and calmer than others.
The relaxed individuals had a 50% less likelihood of developing dementia than the distressed participants.