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.