WEDNESDAY, Nov. 6 (HealthDay News) -- Speaking two languages may help delay the damage of dementia, a new study suggests.

Researchers found that people who were bilingual did not show the signs of three types of dementia, including Alzheimer's disease, for more than four years longer than those who spoke only one language.

The report was published online Nov. 6 in the journal Neurology.

"Bilingualism can be seen as a successful brain training, contributing to cognitive reserve, which can help delay dementia," said study co-author Dr. Thomas Bak, a lecturer at the Center for Cognitive Aging and Cognitive Epidemiology at the University of Edinburgh in Scotland.

Cognitive reserve is the ability of the brain to keep functioning normally despite significant disease or injury, explained Stephen Rao, a neuropsychologist at Cleveland Clinic's Lou Ruvo Center for Brain Health. "It has been understood that this capacity is influenced by education, higher occupational status, engagement in higher order cognitive [thinking] activities, and now bilingualism," Rao said.

People with a greater cognitive reserve experience the onset of dementia later in life than people with less reserve. As a result, the impact of dementia will be less apparent for longer in people with greater reserve capacity, as thinking and memory functions are able to carry on even with the loss of brain cells.

Bak noted that the effect that speaking two languages had in delaying dementia had nothing to do with the level of education of the participants, but may well be another aspect of cognitive reserve.

"The fact that bilingual advantage is not caused by any differences in education is confirmed by the fact that it was also found in illiterates, who have never attended any school," he said.

Another expert agreed.

"This looks to me like a specific effect of language training and plasticity over and above the well-known effect of education," said Dr. Sam Gandy, director of the Mount Sinai Center for Cognitive Health in New York City.

This is reminiscent of the benefit of social engagement that is over and above that of education and mental stimulation, Gandy pointed out.