LOS ANGELES — People who spoke two languages developed dementia 4½ years later than those who spoke just one — even in people who were illiterate, said scientists who reviewed the records of hundreds of dementia patients.
The study is the largest to date to document the delay of dementia in bilingual people and the first to suggest that education level alone can't explain the difference, the researchers said.
The people reviewed lived in Hyderabad, India. Much previous work has been with immigrants who bring a native language to a new culture.
Most people in Hyderabad are at least bilingual. They are exposed to Telugu and Dakhini languages in informal contexts, such as home, and to Hindi and English in school and other formal contexts.
The researchers found that a person didn't get additional advantage by speaking three or more languages.
The advantages — dementia onset at 61.1 years of age for monolingual people, 65.6 for bilingual people — applied to Alzheimer's disease, as well as frontotemporal dementia and vascular dementia.
The results were published online Wednesday in the journal Neurology.