Background Traumatic brain injuries (TBI) among military veterans are increasingly recognized as important causes of both short and long-term neuropsychological dysfunction. However, the association between TBI and the development of dementia is controversial. This systematic review and meta-analysis sought to quantify the risks of all-cause dementia including Alzheimer’s diseases and related dementias (ADRD), and to explore whether the relationships are influenced by the severity and recurrence of head injuries. Methods Database searches of Medline, Embase, Ovid Healthstar, PubMed and PROSPERO were undertaken from inception to December 2020 and supplemented with grey literature searches without language restrictions. Observational cohort studies examining TBI and incident dementia among veterans were analysed using Dersimonian-Laird random-effects models. Results Thirteen cohort studies totalling over 7.1 million observations with veterans were included. TBI was associated with an increased risk of all-cause dementia (hazard ratio [HR] = 1.95, 95% confidence interval [CI]: 1.55–2.45), vascular dementia (HR = 2.02, 95% CI: 1.46–2.80), but not Alzheimer’s disease (HR = 1.30, 95% CI: 0.88–1.91). Severe and penetrating injuries were associated with a higher risk of all-cause dementia (HR = 3.35, 95% CI: 2.47–4.55) than moderate injuries (HR = 2.82, 95% CI: 1.44–5.52) and mild injuries (HR = 1.91, 95% CI: 1.30–2.80). However, the dose–response relationship was attenuated when additional studies with sufficient data to classify trauma severity were included. Conclusion TBI is a significant risk factor for incident all-cause dementia and vascular dementia. These results need to be interpreted cautiously in the presence of significant heterogeneity.

中文翻译：

---

退伍军人的创伤性脑损伤和痴呆症的风险：系统评价和荟萃分析

背景 退伍军人中的创伤性脑损伤 (TBI) 越来越被认为是短期和长期神经心理功能障碍的重要原因。然而，TBI 与痴呆症发展之间的关联存在争议。这项系统评价和荟萃分析旨在量化全因痴呆症的风险，包括阿尔茨海默病和相关痴呆症 (ADRD)，并探讨这些关系是否受到头部损伤严重程度和复发的影响。方法 Medline、Embase、Ovid Healthstar、PubMed 和 PROSPERO 的数据库检索从成立到 2020 年 12 月进行，并辅以灰色文献检索，没有语言限制。使用 Dersimonian-Laird 随机效应模型分析了检查退伍军人 TBI 和事件性痴呆的观察性队列研究。结果 纳入了 13 项队列研究，共对退伍军人进行了超过 710 万次观察。TBI 与全因痴呆风险增加相关（风险比 [HR] = 1.95，95% 置信区间 [CI]：1.55-2.45），血管性痴呆（HR = 2.02，95% CI：1.46-2.80），但不是阿尔茨海默病 (HR = 1.30, 95% CI: 0.88–1.91)。与中度损伤（HR = 2.82, 95% CI: 1.44-5.52）和轻度损伤（HR = 1.91, 95% CI：1.30–2.80)。然而，当纳入有足够数据对创伤严重程度进行分类的其他研究时，剂量-反应关系减弱。结论 TBI是发生全因痴呆和血管性痴呆的重要危险因素。在存在显着异质性的情况下，需要谨慎解释这些结果。