The findings are based on tests on 104 people

Researchers from York University in Canada carried out tests on 104 people between the ages of 30 and 88.

They found that those who were fluent in two languages rather than just one were sharper mentally.

Writing in the journal of Psychology and Ageing, they said being bilingual may protect against mental decline in old age.

Previous studies have shown that keeping the brain active can protect against senile dementia.

Education in general can bestow benefits on cognitive function in later life

Professor Clive Ballard,

Alzheimer's Society

Other activities like doing crosswords or playing board games may also help.

Language skills

This latest study appears to back up the theory that language skills also have a protective effect.

Dr Ellen Bialystok and colleagues at York University assessed the cognitive skills of all those involved in the study using a variety of widely recognised tests.

They tested their vocabulary skills, their non-verbal reasoning ability and their reaction time.

Half of the volunteers came from Canada and spoke only English. The other half came from India and were fluent in both English and Tamil.

The volunteers had similar backgrounds in the sense that they were all educated to degree level and were all middle class.

The researchers found that the people who were fluent in English and Tamil responded faster than those who were fluent in just English. This applied to all age groups.

The researchers also found that the bilingual volunteers were much less likely to suffer from the mental decline associated with old age.

"The bilinguals were more efficient at all ages tested and showed a slower rate of decline for some processes with aging," they said.

"It appears...that bilingualism helps to offset age-related losses."

The UK's Alzheimer's Society welcomed the study.

"These findings, that early development of second language may improve a specific aspect of cognitive function in later life, are very interesting," said Professor Clive Ballard, its director of research.

"It is a possibility that the acquisition of a second language in early childhood may influence the process of the development of neuronal circuits.

"However, the results of this particular study need to be interpreted cautiously as they were comparing groups of individual of different nationalities, educated in different systems.

"It is also well recognised that education in general can bestow benefits on cognitive function in later life."