Supplementary Material for: Leisure-time television viewing and computer use, family history, and incidence of dementia

Background & Objectives: Time spent on screen-based sedentary activities are significantly associated with dementia risk, however, whether the associations vary by family history (FHx) of dementia is currently unknown. We aimed to examine independent associations of two prevalent types of screen-based sedentary activities (television [TV] viewing and computer use) with dementia and assess the modifying effect of FHx. Methods: We included 415,048 individuals free of dementia from the UK Biobank. Associations of TV viewing, computer use, and FHx with dementia risk were determined using Cox regression models. We estimated both multiplicative- and additive-scale interactions between TV viewing and computer use and FHx. Results: During a median follow-up of 12.6 years, 5,549 participants developed dementia. After adjusting for potential confounding factors, we observed that moderate (2-3 h/day; hazard ratio [HR] 1.13, 95% confidence interval [CI] 0.03-1.23) and high (>3 h/day; 1.33, 1.21-1.46) TV viewing was associated with a higher dementia risk, compared with low (0-1 h/day) TV viewing. Using restricted cubic spline models, the relationship of TV viewing with dementia was nonlinear (relative to 0 hour/day; P for nonlinear = 0.005). We found that >3 h/day of TV viewing was associated with a 42% (1.42, 1.18-1,71) higher dementia risk in participants with FHx while a 30% (1.30, 1.17-1.45) in those without FHx. For computer use, both low (0h/day; 1.41, 1.33-1.50) and high (>2h/day; 1.17, 1.05-1.29) computer use were associated with elevated dementia risk, compared with moderate (1-2h/day) computer use. We observed a J-shaped relationship with dementia (relative to 2 hour/day; P for nonlinear < 0.001). Compared with 1-2h/day of computer use, the HRs of dementia were 1.46 (1.29-1.65) and 1.10 (0.90-1.36) for 0h/day and >2h/day of computer use in participants with FHx respectively; while the corresponding HRs were 1.40 (1.30-1.50) and 1.19 (1.06-1.33) in those without FHx. We observed a positive additive interaction (RERI 0.29, 0.06-0.53) between computer use and FHx, while little evidence of interaction between TV viewing and FHx. Conclusions: The adverse effects of time spent on TV viewing or computer use and FHx were independent on dementia risk. Our findings point to new behavioral targets for intervention on preventing an early onset of dementia, especially for those with FHx.

研究背景与研究目的：每日花费在基于屏幕的久坐行为上的时长与痴呆症风险显著相关，但目前尚不明确该关联是否因痴呆症家族史（family history of dementia，FHx）而异。本研究旨在探讨两种常见的基于屏幕的久坐行为——电视（television [TV]）观看与电脑使用——与痴呆症风险的独立关联，并评估痴呆症家族史的调节效应。

研究方法：本研究纳入英国生物样本库（UK Biobank）中415048名无痴呆症病史的参与者。采用Cox回归模型分析电视观看时长、电脑使用时长以及痴呆症家族史与痴呆症风险的关联，并估算电视观看、电脑使用分别与痴呆症家族史之间的相乘尺度交互作用与相加尺度交互作用。

研究结果：中位随访12.6年期间，共有5549名参与者罹患痴呆症。校正潜在混杂因素后，与每日电视观看时长较低（0~1小时）的参与者相比，每日电视观看时长中等（2~3小时；风险比[hazard ratio，HR]=1.13，95%置信区间[confidence interval，CI]=0.03~1.23）与较高（＞3小时；HR=1.33，95%CI=1.21~1.46）均与痴呆症风险升高相关。通过限制性立方样条模型分析发现，电视观看时长与痴呆症风险的关联呈非线性（以每日0小时为参照；非线性检验P值=0.005）。在有痴呆症家族史的参与者中，每日电视观看时长＞3小时与痴呆症风险升高42%（HR=1.42，95%CI=1.18~1.71）相关，而在无家族史的参与者中该风险升高30%（HR=1.30，95%CI=1.17~1.45）。对于电脑使用而言，与每日电脑使用时长中等（1~2小时）的参与者相比，每日使用时长较低（0小时；HR=1.41，95%CI=1.33~1.50）与较高（＞2小时；HR=1.17，95%CI=1.05~1.29）均与痴呆症风险升高相关。电脑使用时长与痴呆症风险呈J型关联（以每日2小时为参照；非线性检验P值＜0.001）。与每日电脑使用时长1~2小时的参与者相比，在有痴呆症家族史的参与者中，每日使用0小时与＞2小时者的痴呆症风险比分别为1.46（95%CI=1.29~1.65）与1.10（95%CI=0.90~1.36）；而在无家族史的参与者中，对应的风险比分别为1.40（95%CI=1.30~1.50）与1.19（95%CI=1.06~1.33）。本研究观察到电脑使用与痴呆症家族史之间存在正向相加交互作用（相对超额交互危险度relative excess risk due to interaction，RERI=0.29，95%CI=0.06~0.53），而未发现电视观看与痴呆症家族史之间存在显著交互作用的证据。

研究结论：电视观看与电脑使用时长以及痴呆症家族史对痴呆症风险的不良影响相互独立。本研究结果为痴呆症预防的干预行为靶点提供了新方向，尤其针对存在痴呆症家族史的人群，有助于延缓痴呆症早发。