Hundreds of people in Spain's Basque region who spoke one to four languages were assessed with AI that estimated brain age from patterns of brain connectivity.
The apparent benefit increased with language count: trilingual participants looked about seven years younger, while people speaking four languages appeared roughly 13 years younger.
Earlier second-language learning and higher fluency were linked to greater gains, and an outside neuroscientist said trials in older adults have also found attention and memory improvements after months of study.
Researchers said the study controlled for age, sex and education but could not rule out other influences such as lifestyle and social engagement.