Speaking more than one language protects the brain against cognitive decline and makes a person better at multi-tasking, researchers say.

Being bilingual, or even learning a second language late in life, has been shown to slow the decline of some key brain functions, said Ellen Bialystok of York University in Canada. A study co-authored by Dr Bialystok found that people who spoke more than one language were diagnosed with Alzheimer's disease 4.3 years later and reported the onset of symptoms 5.1 years later than monolingual patients.

''One of the reasons bilingualism has these powerful mechanisms including protecting against early symptoms of dementia is because it's one way to keep your brain active,'' Dr Bialystok said. ''Every little bit helps.''