Speaking more than one language does not improve a person's general mental ability. However, while there is no cognitive advantage to being bilingual, there are broader social and lifestyle benefits that come from speaking multiple languages.
While being bilingual delays the onset of dementia, the decline into full-blown Alzheimer's disease is more rapid in those who speak two or more languages than in monolingual people.
Bilingual multiple sclerosis patients score better than those who are monolingual in cognitive tests.
While being multilingual did not delay the onset of dementia for those at risk, nuns who spoke four or more languages were significantly less likely to develop dementia than those who spoke just one language.
Living in a linguistically diverse environment helps promote more effective learning of new languages for monolingual people.
By eleven months, infants hold language dependent expectations of a speaker's ethnicity. The study suggests babies make connections between languages based on the individuals they encounter in their environments.
While learning a second language has positive benefits for children, there is little evidence that bilingual children have more advanced executive function or improved attention over those who are monolingual.