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Background: Previous epidemiological studies have reported controversial results on the relationship between smoking and Alzheimer's disease (AD). Therefore, we sought to assess the association using Mendelian randomization (MR) analysis. Methods: We used single nucleotide polymorphisms (SNPs) associated with smoking quantity (cigarettes per day, CPD) from genome-wide association studies (GWAS) of Japanese population as instrumental variables, then we performed two-sample MR analysis to investigate the association between smoking and AD in a Chinese cohort (1,000 AD cases and 500 controls) and a Japanese cohort (3,962 AD cases and 4,074 controls), respectively. Results: Genetically higher smoking quantity showed no statistical causal association with AD risk (the inverse variance weighted (IVW) estimate in the Chinese cohort: odds ratio (OR) = 0.510, 95% confidence interval (CI) = 0.149-1.744, p = 0.284; IVW estimate in the Japanese cohort: OR = 1.170, 95% confidence interval CI = 0.790-1.734, p = 0.434). Conclusion: This MR study, for the first time in Chinese and Japanese populations, found no significant association between smoking and AD. [ABSTRACT FROM AUTHOR]

Background: Many epidemiological studies have reported the association between various social factors and health status in mothers during and after pregnancy. However, little is known about their joint and longitudinal impact. We examined the association of lack of social support and trust during pregnancy and at 2.5 years postpartum with health status in mothers., Methods: To adequately address time-varying exposure, marginal structural models were fitted to a pseudopopulation constructed using inverse probability weighting. The model included records of 90,071 mothers participating in the Japan Environment and Children's Study. Social support and trust were measured using a 9-item questionnaire (Q1-9). Mental and physical health were measured using Mental and Physical Component Summary scores from the 8-item Short-Form Health Survey., Results: For the Mental Component Summary, the magnitude of the effect estimate was largest when participants lacked close friends/neighbors (Q4) at only 2.5 years postpartum (effect estimate, -6.23), followed by a lack in emotional support (Q2) at the same time point (effect estimate, -4.94). For the Physical Component Summary, effect estimates were negligible. The magnitude of the effect estimates of lack of social support and trust tended to be larger when there was a lack at only 2.5 years postpartum than at both time points., Conclusion: These findings suggest that, after childbirth, a loss in social support, particularly in an emotional aspect, carries high risk, especially for mental health. Our results highlight the importance of supporting mothers for more than a few years after pregnancy.