Bilingualism may delay the onset of Alzheimer's disease, a brain scanning study suggests.

The study by Canadian researchers in the journal Cortex offers the first physical evidence that speaking more than one language delays the onset of disease.

In the study, researchers studied CT scans of 40 people who had been diagnosed with Alzheimer's disease. They all had similar levels of education and cognitive skills, such as attention, memory and planning. Half were fluently bilingual and the other half spoke only one language.

"Bilingualism appears to contribute to increased cognitive reserve, thereby delaying the onset of Alzheimer disease and requiring the presence of greater amounts of neuropathology before the disease is manifest," the study's authors wrote.

But bilingualism does not prevent Alzheimer's, said Tom Schweizer, a neuroscientist who headed the research at St. Michael's Hospital in Toronto.

Once Alzheimer's symptoms appear in bilingual people, it is not clear whether the disease progresses at an accelerated rate.

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A pedestrian passes a stop sign displayed in both English and Inuktitut in Iqaluit. Bilingualism appears to contribute to increased cognitive reserve, thereby delaying the onset of Alzheimer's disease, researchers say. (Nathan Denette/Canadian Press)

The bilinguals showed "twice as much damage but were able to maintain their cognitive abilities just as well as the monolingual group. So that was quite striking in the sense that there is something there that is compensating for twice as much disease burden in these patients," said Schweizer.

He said that because bilingual people constantly switch from one language to another or suppress one language to speak in the other, their brains may be better prepared to compensate through enhanced brain networks or pathways when Alzheimer's sets in.

"Maybe bilinguals are building up their brains just like staying in school for four more years or something like that," said Dr. Howard Chertkow, a professor in the department of neurology and neurosurgery at McGill University in Montreal.

No downside to being bilingual

Chertkow, who speaks English and French fluently, called the findings interesting and important.

"There's no downside to be bilingual. If anything, there's a benefit. There's a benefit in your performance in school, in your attention, benefit when you get up to old age in terms of protecting your brain to some extent," Chertkow said.

The study was done in Toronto, where the second language of many study participants was French, English or Chinese.

Schweizer said the results are especially important in Canada, which is officially bilingual and has large numbers of immigrants for whom French and English are at least second languages.

The investigators considered the possibility that factors other than bilingualism contributed to the difference.

But both years of education and occupational status were greater in those speaking one language, which the researchers said works against their hypothesis.

Unanswered questions

Previous studies by the same team suggested the delay in onset of Alzheimer's was not affected by immigrant status.

Researchers still don't know precisely how bilingualism offers an advantage in delaying the disease.

They cautioned that the findings should be interpreted cautiously given the relatively small sample sizes.

The next steps would be to repeat the study in a larger sample of patients followed over time using more sophisticated MRI technology, the researchers said.

Chertkow's main criticism of the study was that the two groups weren't perfectly matched for age since the bilinguals were 1½ years older on average, a slight difference that could contribute.

More studies are also needed to find whether a second language has to be learned early in life to provide maximum benefit.

In the meantime, Jim Finkbeiner of Exeter, Ont. is trying to learn French. Since Finkbeiner was diagnosed with Alzheimer's two years ago, his symptoms haven't gotten worse.

"I figure if I stop and don't work at it, I'm not going to last long," he said.

The study was funded by the Alzheimer Society of Canada and the Canadian Institutes of Health Research.

With files from CBC's Ioanna Roumeliotis