A study of 600 stroke victims found 40.5% who were multilingual had normal mental functions afterwards, compared to 19.6% who only speak one language.
The Edinburgh University study took into account smoking, high blood pressure, diabetes and age.
It worked with the Nizam Institute of Medical Sciences in India.
The study was conducted in Hyderabad because its multi-cultural nature means many languages are commonly spoken.
The study, published in the American Heart Association journal Stroke, found “results support the notion of a protective role of bilingualism in the development of post-stroke cognitive impairment”.
It is the first time a study has been done looking at the relationship between the number of languages spoken and a patient’s cognitive outcome after stroke.
The paper said: “The percentage of patients with intact cognitive functions post-stroke was more than twice as high in bilinguals than in monolinguals.
“In contrast, patients with cognitive impairment were more common in monolinguals.”
Researchers believe the study, which was funded by the Indian Council of Medical Research, suggests the mental challenge of speaking multiple languages can boost cognitive reserve – an improved ability of the brain to cope with damaging influences such as stroke or dementia.
Co-author Thomas Bak, of the University of Edinburgh’s school of philosophy, psychology and language sciences, said: “Bilingualism makes people switch from one language to another, so while they inhibit one language, they have to activate another to communicate.
“This switching offers practically constant brain training which may be a factor in helping stroke patients recover.”