Smoking cessation and incident dementia in elderly Japanese: the Ohsaki Cohort 2006 Study
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NEURO-EPIDEMIOLOGY
Smoking cessation and incident dementia in elderly Japanese: the Ohsaki Cohort 2006 Study Yukai Lu1 · Yumi Sugawara1 · Shu Zhang1 · Yasutake Tomata1 · Ichiro Tsuji1 Received: 14 June 2019 / Accepted: 3 February 2020 © The Author(s) 2020
Abstract To investigate the association of smoking status and years since smoking cessation with the risk of incident dementia among elderly Japanese. We conducted a longitudinal analysis of smoking status and smoking cessation with dementia in prospective cohort study of 12,489 Japanese individuals aged ≥ 65 years who were followed up for 5.7 years. Information on smoking status and other lifestyle factors was collected via a questionnaire in 2006. Data on incident dementia were retrieved from the public Long-term Care Insurance Database. The Cox proportional hazards model was used to estimate the multivariableadjusted hazard ratios (HRs) and 95% confidence intervals (95% CIs) for incident dementia. During 61,613 person-years of follow-up, 1110 cases (8.9%) of incident dementia were documented. Compared with individuals who had never smoked, current smokers showed a higher risk of dementia (HR 1.46, 95% CI 1.17, 1.80). Among ex-smokers, the risk for those who had stopped smoking for ≤ 2 years was still high (HR 1.39, 95% CI 0.96, 2.01), however, quitting smoking for 3 years or longer mitigated the increased risk incurred by smokers; the multivariable HRs (95% CIs) were 1.03 (0.70, 1.53) for those who had stopped smoking for 3–5 years, 1.04 (0.74, 1.45) for 6–10 years, 1.19 (0.84, 1.69) for 11–15 years, and 0.92 (0.73, 1.15) for > 15 years. Our study suggests that the risk of incident dementia among ex-smokers becomes the same level as that of never smokers if they maintain abstinence from smoking for at least 3 years. Keywords Smoking · Smoking cessation · Incident dementia · Cohort study · Elderly population
Introduction Dementia is a major cause of disability and dependency among the elderly, having a significant impact on individuals as well as families, communities and societies. In 2015, dementia affected about 47 million people worldwide, and it is estimated that globally nearly 9.9 million people develop dementia each year [1]. Thus, it is critical to identify more modifiable factors to reduce the incidence of dementia. The association between smoking status and dementia has been examined extensively [2–12], and a recent meta-analysis Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10654-020-00612-9) contains supplementary material, which is available to authorized users. * Yumi Sugawara [email protected] 1
Division of Epidemiology, Department of Health Informatics and Public Health, Tohoku University School of Public Health, Graduate School of Medicine, 2‑1 Seiryo‑machi, Aoba‑ku, Sendai, Miyagi 980‑8575, Japan
indicated that current smokers have a significantly higher risk of dementia [13]. However, it has been suggested that smoking cessation would attenuate the excess risk of dementia
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