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Background: Large population-based prospective studies are necessary to provide clarification on the associations of panoramic secondhand smoking burden, including prenatal and postnatal secondhand smoke (SHS) exposure, with the risk of developing dementia. Methods: Our study comprised a sample of 353,756 dementia-free individuals from the UK Biobank who were nonsmokers had data on the exposure of maternal smoking as well as SHS exposure in daily life, which was quantified in terms of hours per week (h/week) and whether they lived with household smokers. Multivariable Cox regression models were utilized to analyze the independent and joint associations of maternal smoking and daily life SHS exposure with dementia risk. Results: During a median follow-up of 11.8 years, 4,113 participants developed dementia. Compared with those who lived in the environment without smokers, multivariable-adjusted hazard ratios (HRs) (95% CIs) were 1.11 (1.02, 1.20) and 1.31 (1.13, 1.52) for those who exposed to SHS for >0 but ≤4 h/week and >4 h/week, respectively, and was 1.25 (1.13, 1.39) for those who lived with smokers in the household. A positive history of maternal smoking was associated with a modestly higher risk of dementia (HR = 1.07; 95% CI: 1.01, 1.15). Furthermore, compared with participants with neither history of maternal smoking nor exposure to SHS, a particularly higher risk of dementia was observed among those with both exposures (HR = 1.48; 95% CI: 1.18, 1.86). Additionally, the HR (95% CI) was 1.32 (1.10, 1.59) when comparing participants with a history of maternal smoking who lived with smokers in their households with those who had neither exposures. Conclusions: Having a history of maternal smoking, longer exposure to SHS, and living with smokers in the household were each associated with an increased risk of developing dementia. Individuals who were simultaneously exposed to maternal smoking and SHS or lived with household smokers had a particularly higher dementia risk. [ABSTRACT FROM AUTHOR]

Background: The influence of overall air pollution on dementia risk and the potential effect modification by other risk factors remain to be clarified.Methods: We selected 459,844 UK residents who were free of dementia and had data on the exposure to PM2.5, PM2.5-10, PM10, NO2, and NOx during baseline recruitment. The combined exposure to various PMs and NOx was estimated by using an air pollution score. Hazard ratios (HRs) and 95% confidence intervals (CIs) for incident dementia were estimated by Multivariable Cox models.Results: During a median 11.7 years of follow-up, 5,905 incident cases of all-cause dementia were identified. With the exception of PM2.5-10, all other air pollutants were separately associated with a higher risk of all-cause dementia (all P-trend <0.001) with generally similar associations for dementia subtypes. An increasing air pollution score was associated with higher risks of all-cause as well as individual dementia outcomes, with adjusted HRs (95% CI) of 1.27 (1.18, 1.37) for all-cause dementia, 1.27 (1.14, 1.43) for Alzheimer's disease, and 1.35 (1.16, 1.57) for vascular dementia when comparing the highest with the lowest quartile of the score (all P-trend <0.001). These associations of air pollution score with dementia and its subtypes were observed among never and former smokers but not among current smokers (all P-interaction <0.030).Conclusions: Air pollution was associated with higher risk of dementia among nonsmokers but not current smokers. Additional studies are required to confirm our findings and to explore the potential mechanisms underlying the possible effect modification by smoking status. [ABSTRACT FROM AUTHOR]