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.
"This is unheard of — no medicine comes close to delaying the onset of symptoms and now we have the evidence to prove this at the neuroanatomical level," Tom Schweizer, a neuroscientist who headed the research, said in a release.
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.
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But bilingualism does not prevent Alzheimer's, Schweizer noted. Once Alzheimer's symptoms appear in bilingual people, it is not clear whether the disease progresses at an accelerated rate.
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. 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.
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.
More studies are also needed to find you whether a second language has to be learned early in life to provide maximum benefit.
The study was funded by the Alzheimer Society of Canada and the Canadian Institutes of Health Research.