People who speak more than one language tend to develop dementia up to five years later than those who are monolingual, new research reveals.

Investigators at the Nizam Institute of Medical Sciences in India and the University of Ediburgh looked at close to 650 dementia patients. There were 391 patients who spoke two or more languages, and they had a later date of diagnosis for Alzheimer’s disease, vascular dementia and frontotemporal dementia.

Around 14% of the patients studied were illiterate. Formal language education did not make a difference in delayed onset, the authors said, suggesting that bilingual switching between words, concepts, grammar, sounds and social norms created a form of “natural” brain training.

The results suggest “bilingualism might have a stronger influence on dementia that any currently available drugs,” said Thomas Bak, Ph.D., of the University of Edinburgh’s School of Philosophy, Psychology and Language Science.

Results were published in Neurology on Nov. 6. A 2010 study, also published in Neurology, also found “bilingualism confers protection against the onset of AD,” the authors wrote.