How strong is the evidence for Multilingualism?

Multilingualism has one of the more geographically consistent evidence bases in dementia research, though two recent meta-analyses converge on an important nuance: it appears to delay when symptoms appear, not whether dementia develops at all. That evidence is currently rated moderate (67/100), built on 7 published studies, including 2 meta-analyses -- a reasonable base, but not yet enough for full certainty.