A robust body of reviews and neuroimaging studies indicates that lifelong bilingualism contributes to cognitive reserve, helping to delay the onset of clinical symptoms of dementia and Alzheimer's disease, although some researchers continue to examine mixed findings and methodological variables.
The retrieved literature predominantly supports the claim that lifelong bilingualism delays the onset of cognitive decline and dementia through mechanisms of cognitive reserve and neuroprotection (Papers 0, 2, 6, 8, 9). While a couple of sources point out mixed findings or methodological inconsistencies in the broader literature (Papers 4, 10), the weight of evidence clearly favors the protective effect, warranting a verdict of SUPPORTED.