Speaking a second language may slow the rate at which the brain declines with age, showing that bilingual people are better protected against Alzheimer's disease than people who use only one language.
Several studies have now demonstrated a clear link between using a second language and cognitive decline, which can be explained by the idea that bilingualism acts like a "mental gymnasium" that keeps the brain active in later life, scientists said.
The latest study, presented to the American Association for the Advancement of Science in Washington, found bilingual patients with probable Alzheimer's were more likely have delayed symptoms compared to monolingual patients. In fact, the effect of speaking a second language produced a stronger effect on delaying the onset of Alzheimer's than any drug currently used to control the disease, said Ellen Bialystok, professor of psychology at York University in Toronto, Canada.
"The finding of a four- to five-year delay in the onset of symptoms of Alzheimer's disease is dramatic. There are no pharmacologic interventions that have shown comparable effects." Our interpretation of the present findings is that bilingualism is a cognitively demanding condition that contributes to cognitive reserve in much the same way as do other stimulating intellectual and social activities."
The researchers believe the effect is directly connected with using a second language, rather than a side-effect of differences in occupation or education between bilingual and monolingual people. Experiments suggest it has something to do with the extra mental effort that goes into using a second language, Professor Bialystok said.
"Being bilingual has certain cognitive benefits and boosts the performance of the brain especially one of the most important areas known as the executive control system. We know that this system deteriorates with age but we have found at every stage of life it functions better in bilinguals. They perform at a higher level.
"It is rather like a reserve tank in a car. When you run out of fuel, you can keep going for longer because there is a bit more in the safety tank," she said.
Judith Kroll, professor of psychology at Penn State University in Pennsylvania, said recent studies have shown that juggling two or more languages helps to exercise the brain and keeps it fit in the elderly. The bottom line is that bilingualism is good for you."
Bilingual people engage in "code switching", mental negotiations between which language they are using.