Bilingualism Is Associated with a Delayed Onset of Dementia but Not with a Lower Risk of Developing it: a Systematic Review with Meta-Analyses.
Level 4 - case-series / case-control
Systematic review and meta-analysis of cross-sectional studies
PubMed 32036490 · doi:10.1007/s11065-020-09426-8
What was done
Method and design, enough to judge the result. From the abstract only. The authors conducted a systematic review and meta-analysis of cross-sectional studies evaluating whether bilingualism is associated with delayed symptom onset, age at diagnosis, and risk of developing mild cognitive impairment (MCI), Alzheimer's disease (AD), or dementia. Disease severity at dementia diagnosis was evaluated as a secondary outcome.
What was found
The actual numbers and directions reported. Not a paraphrase of the conclusion; if the abstract gives no numbers, say so. Bilinguals reported experiencing AD symptoms 4.7 years later than monolinguals (95% CI: 3.3, 6.1) and were diagnosed with dementia 3.3 years later (95% CI: 1.7, 4.9; 95% prediction intervals: -1.9 to 8.5). In subgroup analyses by diagnosis type, bilinguals vs. monolinguals were 1.9 years older at dementia diagnosis (95% CI: -0.9, 4.7) and 4.2 years older at AD diagnosis (95% CI: 2.0, 6.4). There was no significant difference in age at MCI diagnosis (mean difference: 3.2; 95% CI: -3.4, 9.7), overall risk of developing dementia (odds ratio: 0.89; 95% CI: 0.68-1.16), or disease severity at dementia diagnosis (Hedges' g = 0.05; 95% CI: -0.13, 0.24).
Why it matters
What this paper adds. One or two sentences, no hype. This meta-analysis suggests bilingualism is associated with older age at symptom onset and diagnosis for Alzheimer's disease and dementia, though it is not associated with an overall lower risk of developing dementia.
Limits
Sample size, population, design weaknesses, what was not measured. This section is mandatory and must be substantive. The review was limited to cross-sectional studies with substantial unexplained heterogeneity and wide prediction intervals. The abstract notes methodological limitations including poor measurement of language profiles, potential confounding by factors like immigration status, and the inclusion of differing dementia etiologies; total participant count and number of included studies were not reported.
Cited by
- context Learning a new language is associated with a decrease in the risk of Alzheimer's disease.