Pessimistic, anxious and depressed people may have a higher risk of dementia, U.S. researchers reported.

A study of a group of 3,500 people showed that those who scored high for pessimism on a standardized personality test had a 30 percent increased risk of developing dementia 30 to 40 years later.

Those scoring very high on both anxiety and pessimism scales had a 40 percent higher risk, the study showed.

"There appears to be a dose-response pattern, i.e., the higher the scores, the higher the risk of dementia," Dr. Yonas Geda, a neuropsychiatrist at the Mayo Clinic in Rochester, Minnesota who led the study, said in a statement.

Geda and colleagues looked at the medical records of 3,500 men and women who lived near the clinic between 1962 and 1965.

They all took the Minnesota Multiphasic Personality Inventory, a standard personality and life experience test, Geda's team told a meeting of the American Academy of Neurology in Miami.

In 2004 the team interviewed the participants or family members.

Those who scored higher for anxiety and pessimism on the test were more likely, as a group, to have developed dementia by 2004, including Alzheimer's disease and vascular dementia.

This did not mean a person who is pessimistic could assume he or she has a higher risk of developing dementia.

"One has to be cautious in interpreting a study like this," Geda said.

"One cannot make a leap from group level data to the individual. Certainly the last thing you want to do is to say, 'Well, I am a pessimist; thus, I am doomed to develop dementia 20 or 30 years later,' because this may end up becoming a self-fulfilling prophecy."

And there is not any specific way to prevent dementia, although many studies have shown that a healthy diet, exercise, keeping active in other ways, doing puzzles and other activities lower the risk.