Mukadam Naaheed, Sommerlad Andrew, Livingston Gill
J Alzheimers Dis. 2017;58(1):45-54. doi: 10.3233/JAD-170131.
Bilingualism may contribute to cognitive reserve, protect against cognitive decline, and delay the onset of dementia.
We systematically reviewed evidence about the effect of bilingualism on subsequent cognitive decline or dementia.
We searched electronic databases and references for longitudinal studies comparing cognitive decline in people who were bilingual with those who were monolingual and evaluated study quality. We conducted meta-analyses using random effects models to calculate pooled odds ratio of incident dementia.
We included 13/1,156 eligible articles. Meta-analysis of prospective studies of the effects of bilingualism on future dementia gave a combined Odds Ratio of dementia of 0.96 (95% CI 0.74-1.23) in bilingual participants (n = 5,527) compared to monolinguals. Most retrospective studies found that bilingual people were reported to develop symptoms of cognitive decline at a later age than monolingual participants.
We did not find that bilingualism protects from cognitive decline or dementia from prospective studies. Retrospective studies are more prone to confounding by education, or cultural differences in presentation to dementia services and are therefore not suited to establishing causative links between risk factors and outcomes.
双语能力可能有助于认知储备，预防认知能力下降，并延缓痴呆症的发病。
我们系统地回顾了关于双语能力对后续认知能力下降或痴呆症影响的证据。
我们在电子数据库和参考文献中搜索了纵向研究，比较双语者和单语者的认知能力下降情况，并评估研究质量。我们使用随机效应模型进行荟萃分析，以计算痴呆症发病的合并比值比。
我们纳入了1156篇合格文章中的13篇。对双语能力对未来痴呆症影响的前瞻性研究进行荟萃分析，结果显示，与单语者相比，双语参与者（n = 5527）患痴呆症的合并比值比为0.96（95%置信区间0.74 - 1.23）。大多数回顾性研究发现，据报道双语者出现认知能力下降症状的年龄比单语参与者晚。
我们在前瞻性研究中未发现双语能力可预防认知能力下降或痴呆症。回顾性研究更容易受到教育因素或向痴呆症服务机构就诊时文化差异的干扰，因此不适合确定风险因素与结果之间的因果关系。
