Cynical distrust, which is defined as the belief that others are mainly motivated by selfish concerns, has been associated with other health problems, such as heart disease.
This is the first study to look at the relationship between cynicism and dementia, researchers said.
"These results add to the evidence that people's view on life and personality may have an impact on their health," said study author Anna-Maija Tolppanen, of the University of Eastern Finland in Kuopio.
"Understanding how a personality trait like cynicism affects risk for dementia might provide us with important insights on how to reduce risks for dementia," Tolppanen said.
For the study, 1,449 people with an average age of 71 were given tests for dementia and a questionnaire to measure their level of cynicism.
The questionnaire has been shown to be reliable, and people's scores tend to remain stable over periods of several years.
People are asked how much they agree with statements such as "I think most people would lie to get ahead," "It is safer to trust nobody" and "Most people will use somewhat unfair reasons to gain profit or an advantage rather than lose it."
Based on their scores, participants were grouped in low, moderate and high levels of cynical distrust.
A total of 622 people completed two tests for dementia, with the last one an average of eight years after the study started.
During that time, 46 people were diagnosed with dementia. Once researchers adjusted for other factors that could affect dementia risk, such as high blood pressure, high cholesterol and smoking, people with high levels of cynical distrust were three times more likely to develop dementia than people with low levels of cynicism.
Of the 164 people with high levels of cynicism, 14 people developed dementia, compared to nine of the 212 people with low levels of cynicism.
The study also looked at whether people with high levels of cynicism were more likely to die sooner than people with low levels of cynicism.
A total of 1,146 people were included in this part of the analysis, and 361 people died during the average of 10 years of follow-up.
High cynicism was initially associated with earlier death, but after researchers accounted for factors such as socioeconomic status, behaviours such as smoking and health status, there was no longer any link between cynicism and earlier death.
The study was published in Neurology, the medical journal of the American Academy of Neurology.