Biomarker assessment of tobacco smoking exposure and risk of dementia death: pooling of individual participant data from 14 cohort studies.

BACKGROUND: While there is a suggestion that self-reported tobacco smoking may be a risk factor for dementia, to date, it has not been possible to explore the thresholds at which this exposure elevates risk. Accordingly, our aim was to relate cotinine, a biomarker of tobacco smoking, to risk of dementia death.
METHODS: We pooled 14 prospective cohort studies that held data on cotinine (plasma or saliva), covariates and death records.
RESULTS: In the 33 032 study members (17 107 women) with salivary cotinine data, a mean duration of 8.3 years of follow-up gave rise to 135 deaths ascribed to dementia; while in 15 130 study members (7995 women) with plasma cotinine data, there were 119 dementia deaths during 14.3 years of mortality surveillance. After multiple adjustment, both plasma cotinine (per 1 SD higher cotinine; 95% CI 1.29; (1.05 to 1.59)) and salivary cotinine (1.10 (0.89 to 1.36)) were positively related to dementia risk, with stronger effects apparent for plasma.
CONCLUSION: Our finding that plasma cotinine was related to an elevated risk of dementia death warrants testing in studies with measures of disease onset as opposed to just mortality. © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.