Being able to speak more than one language may delay the onset of dementia, a new study has discovered.

Researchers at Edinburgh University and Nizam’s Institute of Medical Sciences in Hyderabad, India worked together on the study, which has been published in the journal Neurology. By examining hundreds of patients diagnosed with the degenerative condition, they discovered that being able to speak two or more languages delayed the onset of the disease by as long as five years.

According to the research, three types of dementia – Alzheimer’s disease, frontotemporal dementia and vascular dementia – were delayed by being able to speak two languages. This trend was also seen among subjects who were illiterate; possibly suggesting that this language ability is more influential than reading and writing.

The researchers analysed data on 648 people in Hyderabad, India, all of whom had been diagnosed with some form of dementia. The average age of the group was 66 years old, and it was discovered that typically the ability to speak two languages had delayed the onset of the disease by approximately four and a half years.

India was an interesting location for the researchers to base their study on. This summer, the People’s Linguistic Survey of India published the most comprehensive survey to be carried out in decades on the country’s languages. According to the poll, there are 780 languages spoken across the nation, although the experts behind the research estimated the real number could be closer to 880. This is because some languages are spoken by so few people they may have been missed out.

While this survey revealed a vast number of languages are spoken throughout India, it also discovered that in the last 50 years more than 200 languages native to the country have become extinct. Others are only spoken by a handful of people. The language of Majhi, for example, was found to only have four fluent speakers, in comparison to Hindi, which is spoken by an estimated 400 million people across India.

Hyderabad was chosen as the base for the study into how bilingualism can slow cognitive decline because speaking two languages is part of everyday life for many of the people who live there. Indeed, monolingual people are in the minority.

The researchers concluded that speaking two languages improves the development of some parts of the brain. Because some of the subjects could not read, the researchers also theorised that formal education did not go far enough in explaining the differences in the onset of cognitive decline.

Suvarna Alladi, the study’s author from Nizam’s Institute of Medical Sciences in Hyderabad, said: “These results offer strong evidence for the protective effect of bilingualism against dementia in a population very different from those studied so far in terms of its ethnicity, culture and patterns of language use.” Meanwhile, Thomas Bak, a researcher at the University of Edinburgh, explained the results suggested bilingual abilities are more influential on the development of dementia than any of the drugs that are currently available. “This makes the study of the relationship between bilingualism and cognition one of our highest priorities,” he concluded.