Among people who develop dementia, onset of the disease may be delayed in those who can speak more than one language, a new study indicates.

Scientists in India assessed almost 650 people with dementia and found that those who spoke at least two languages developed different forms of the condition, including Alzheimer's disease, up to five years later than those who only spoke one language.

The study found that this link also applied to people who were illiterate and who had not attended school. This, the scientists said, shows that the results are not linked to differences in education levels.

They acknowledged that further research is needed to uncover why this link exists. However they suggested that the work involved in speaking more than one language, such as switching between sounds, concepts and grammar, may act as a form of natural brain training.

"These findings suggest that bilingualism might have a stronger influence on dementia that any currently available drugs. This makes the study of the relationship between bilingualism and cognition one of our highest priorities," the team said.

Details of these findings are published in the journal, Neurology.

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