Being able to speak more than one language may help you think more clearly in later life， even if you’ve learned the second language as an adult， according to a new study.

Thomas H. Bak of the University of Edinburgh Center for Cognitive Aging and Cognitive Epidemiology， the author of the new paper， said previous studies had shown that “bilinguals” who suffered dementia began showing symptoms four to five years later than people who spoke only one language. But causality was not clear: Does mastering a second tongue keep brains active longer， or do people with that skill start off with healthier brains than those who don’t?

“That is a very difficult question to address，” Bak said， “and we needed a very special population to do it.”

In his new study， older bilinguals performed better on cognitive tests than monolinguals， even when they had not scored better on intelligence testing decades earlier. That means that， at least in part， learning another language does predict brain health in old age， Bak said.