Association between environmental tobacco smoke exposure and dementia syndromes.

Objectives: Environmental tobacco smoke (ETS) has a range of adverse health effects, but its association with dementia remains unclear and with dementia syndromes unknown. We examined the dose-response relationship between ETS exposure and dementia syndromes.
Methods: Using a standard method of GMS, we interviewed 5921 people aged ≥60 years in five provinces in China in 2007-2009 and characterised their ETS exposure. Five levels of dementia syndrome were diagnosed using the Automated Geriatric Examination for Computer Assisted Taxonomy instrument. The relative risk (RR) of moderate (levels 1-2) and severe (levels 3-5) dementia syndromes among participants exposed to ETS was calculated in multivariate adjusted regression models.
Results: 626 participants (10.6%) had severe dementia syndromes and 869 (14.7%) moderate syndromes. Participants exposed to ETS had a significantly increased risk of severe syndromes (adjusted RR 1.29, 95% CI 1.05 to 1.59). This was dose-dependently related to exposure level and duration. The cumulative exposure dose data showed an adjusted RR of 0.99 (95% CI 0.76 to 1.28) for >0-24 level years of exposure, 1.15 (95% CI 0.93 to 1.42) for 25-49 level years, 1.18 (95% CI 0.87 to 1.59) for 59-74 level years, 1.39 (95% CI 1.03 to 1.84) for 75-99 level years and 1.95 (95% CI 1.34 to 2.83) for ≥100 level years. Significant associations with severe syndromes were found in never smokers and in former/current smokers. There were no positive associations between ETS and moderate dementia syndromes.
Conclusions: ETS should be considered an important risk factor for severe dementia syndromes. Avoidance of ETS may reduce the rates of severe dementia syndromes worldwide.