Being able to speak two languages fluently may delay the onset of Alzheimer's disease by up to five years, a new study suggests.

Dementia currently affects around 36 million people worldwide, including some 40,000 people in Ireland. Alzheimer's disease is the most common type of dementia, accounting for up to 80% of all cases.

Scientists in Belgium looked at 134 people with Alzheimer's disease. Just over half of the participants were monolingual - they spoke one language fluently - while the remainder were bilingual - they spoke two languages fluently.

The study found that the age that Alzheimer's began to manifest itself in monolinguals was 71. However, in bilinguals, it was 76.

A similar difference was found when it came to the diagnosis of the disease. Monolinguals were diagnosed around the age of 72, while bilinguals were diagnosed around the age of 77.

The study took into account other factors that may have influenced the results, such as education and socioeconomic status.

According to the scientists from Ghent University, their findings confirm the results of previous studies which suggested that being bilingual can slow down cognitive ageing.

They added that having to constantly control two languages acts as a workout for the brain, helping to protect its grey cells.

Details of these findings are published in the journal, Bilingualism: Language and Cognition.

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