The article provides a summary of research on a very complex topic and it appears as usual there's no simple "answer". It seems a pretty safe bet that bilingua

The article provides a summary of research on a very complex topic and it appears as usual there's no simple "answer". It seems a pretty safe bet that bilingualism confers some advantages, though the challenge is to try to differentiate just what those are and aren't. The researcher's problem is the enormous overlap of factors affecting cognitive function. For example, psychiatric disorders are quite common and associated with deficits in executive functioning, which we might reason affects capacity to become bilingual in the first place, thus a variable to be controlled. However it's also been shown that biological relatives of psychiatrically disordered individuals have similar (if less severe) deficits. Dispersed into the general population, it's difficult to screen for the potential confound, injecting a subtle and essentially incomputable bias into the comparisons of bi- vs. monolingual individuals. Similarly, the association with earlier or later onset of dementia is extremely difficult to parse. We're back to the usual pulpit re: correlation vs. causation. It could be argued that bilingualism is one indicator of advantaged systemic integrity. There are no doubt many other signals of such advantage. Dementia could be the outcome of an intrinsic lack of fitness in the Darwinian sense.