Lifelong bilingualism can help delay the onset of Alzheimer's disease and other dementia in the elderly by an average of four years, according to a small study by Canadian researchers.

Patients who spoke more than one language reported memory loss or other dementia symptoms on average four years later than people who spoke only one language.

Researchers with the Rotman Research Institute at the Baycrest Research Centre for Aging and the Brain in Toronto carried out the study and published their findings in the February 2007 issue of Neuropsychologia.

Principal investigator Ellen Bialystok, a psychologist and associate scientist at the Rotman Research Institute at Baycrest, said the results were unusually clear.

"Rarely does a study give such clean results, so this was surprising to us," she told CBC News Online.

Bilingualism forces the control functions of the brain's frontal lobe into action, said Bialystok, who conducted the research with psychologist Fergus Craik and neurologist Morris Freedman.

"If you have two languages in your brain, you need a way to keep them straight, otherwise you might say the wrong thing," she said.

"It's one of the things that often goes wrong with people suffering from dementia. They can no longer control their speech."

The frontal lobes, which control planning and other high-level functions, are also used in language. Research has found exercising that part of the brain can help build up a "cognitive reserve," which can stave off dementia.

The study follows earlier work in which Bialystok and colleagues showed bilingualism enhances attention and cognitive control in both children and older adults.

Scientists have increasingly studied activities that help build cognitive reserve in later years. Studies have found evidence that physical activity, social engagement and mental activities such as reading and doing crossword puzzles can also help stave off dementia.

For people who might hear this news and rush off to take Spanish lessons or enrolling in French immersion classes, Bialystok cautioned the study dealt only with lifelong bilingualism.

"We're talking about lifelong bilingualism, so we're talking about people who speak fluently in both languages and use them all the time in daily life," she said.

No tests have been done on trilingual subjects, she said, although she suspects that speaking more than two languages wouldn't have any further effect on cognitive reserves.

"My feeling is it wouldn't make a difference," she said. "The leap in the brain is really from one to two."

Researchers looked at record of 184 patients

The study looked at the diagnostic records of 184 patients who visited Baycrest's Sam and Ida Ross Memory Clinic between 2002 and 2005 complaining of cognitive issues. Of that group, 93 were bilingual and 91 were monolingual.

The bilingual patients included speakers of 25 different languages, the most common being Polish, Yiddish, German, Romanian and Hungarian.

Researchers determined from records of interviews with patients and caregivers that the mean age of dementia symptoms was 71.4 years for the monolingual group and 75.5 years for the bilingual group.

The researchers are working on further studies, in which they will interact with the patients.