Does a second language or music help protect the brain against ageing?

People who speak two or more languages daily have, on average, better cognitive functioning in old age than monolinguals. This is consistently visible across multiple studies involving hundreds to thousands of participants. An Indian study of people aged 60 and over found dementia in 4.9% of monolinguals versus 0.4% of bilinguals. A large European study (more than 86,000 participants from 27 countries) found that multilinguals had nearly twice as low a chance of accelerated biological ageing. A Scottish long-term study, in which the same people were tested at age 11 and again at age 70-plus, showed that bilinguals performed better than would be expected based on their early intelligence, even if they had learned the second language only as an adult.

The mechanism behind this advantage is called cognitive reserve: the brains of bilinguals appear to be more resistant to damage before symptoms become apparent. They show signs of dementia later, their cognition is better than one would expect given comparable brain pathology, and their decline proceeds more slowly in the later stages.

When you learn the second language does, however, matter. In the DELCODE study (746 participants), people who had used a second language daily early in life (between the ages of 13 and 30) benefited the most: they scored better on memory, working memory and executive functions. Those who became bilingual only in middle age had only a memory advantage. Those who started only in later life saw no measurable effect.

The evidence is not without dissenting voices. The large American SALSA study (1,499 older Latinos, followed for nine years) found no protective effect of bilingualism on the rate of cognitive decline. Another study of Mexican-American older adults also found no association between the degree of bilingualism and cognitive test scores after accounting for education and other factors. This suggests that the population group, the timing of measurement and the way of testing can strongly influence the picture.

No data on music are available in the studies provided, so that part of the question cannot be answered on the basis of this research. As far as bilingualism is concerned, daily active use counts the most. Learning a second language without speaking it regularly is unlikely to yield a cognitive benefit.