Published 12 February 2009, doi:10.1136/bmj.b462
Cite this as: BMJ 2009;338:b462

Research

Exposure to secondhand smoke and cognitive impairment in non-smokers: national cross sectional study with cotinine measurement

¹ Department of Public Health and Primary Care, University of Cambridge, Cambridge CB2 2SR, ² Public Health and Epidemiology Group, Peninsula Medical School, Exeter, ³ Department of Internal Medicine, University of Michigan, USA, ⁴ Veterans Affairs Center for Practice Management and Outcomes Research, Michigan, ⁵ Institute for Social Research, University of Michigan, ⁶ MRC Biostatistics Unit, Institute of Public Health, Cambridge

Objective To examine the association between a biomarker of exposure to secondhand smoke (salivary cotinine concentration) and cognitive impairment.

Design Cross sectional analysis of a national population based study.

Setting Stratified random sample of households throughout England.

Participants 4809 non-smoking adults aged 50 years or more from the 1998, 1999, and 2001 waves of the Health Survey for England who also participated in the 2002 wave of the English Longitudinal Study of Ageing and provided saliva samples for cotinine assay and a detailed smoking history.

Main outcome measure Cognitive impairment as defined by the lowest 10% of scores on a battery of neuropsychological tests.

Results Participants who did not smoke, use nicotine products, or have salivary cotinine concentrations of 14.1 ng/ml or more were divided into four equal size groups on the basis of cotinine concentrations. Compared with the lowest fourth of cotinine concentration (0.0-0.1 ng/ml) the odds ratios (95% confidence intervals) for cognitive impairment in the second (0.2-0.3 ng/ml), third (0.4-0.7 ng/ml), and highest fourths (0.8-13.5 ng/ml) were 1.08 (0.78 to 1.48), 1.13 (0.81 to 1.56), and 1.44 (1.07 to 1.94; P for trend 0.02), after adjustment for a wide range of established risk factors for cognitive impairment. A similar pattern of associations was observed for never smokers and former smokers.

Conclusions Exposure to secondhand smoke may be associated with increased odds of cognitive impairment. Prospective nationally representative studies relating biomarkers of exposure to cognitive decline and risk of dementia are needed.

© Llewellyn et al 2009
This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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