Exposure to secondhand smoke and cognitive impairment in non-smokers: national cross sectional study with cotinine measurementBMJ 2009; 338 doi: https://doi.org/10.1136/bmj.b462 (Published 12 February 2009) Cite this as: BMJ 2009;338:b462
- David J Llewellyn, research associate1,
- Iain A Lang, research fellow2,
- Kenneth M Langa, associate professor of internal medicine345,
- Felix Naughton, doctoral researcher1,
- Fiona E Matthews, senior research scientist6
- 1Department of Public Health and Primary Care, University of Cambridge, Cambridge CB2 2SR
- 2Public Health and Epidemiology Group, Peninsula Medical School, Exeter
- 3Department of Internal Medicine, University of Michigan, USA
- 4Veterans Affairs Center for Practice Management and Outcomes Research, Michigan
- 5Institute for Social Research, University of Michigan
- 6MRC Biostatistics Unit, Institute of Public Health, Cambridge
- Correspondence to: D J Llewellyn
- Accepted 13 November 2008
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.
We thank Fiona McDougall (University of Cambridge) and Robert Friedland (Case Western Reserve University) for their suggestions.
Contributors: DJL conceived the study, acquired the data, did the statistical analysis, and is guarantor. All authors participated in the management, analysis, interpretation of data, and drafting of the manuscript. All have critically revised the manuscript for important intellectual content and seen and approved the final version.
Funding: The English Longitudinal Study of Ageing is funded by the US National Institute on Aging and a consortium of UK government departments. KML was supported by grants from the US National Institute on Aging (K08 AG019180 and R01 AG027010) and a Paul Beeson Physician Faculty Scholars in Aging Research award. IAL is an academic specialty registrar in public health supported by the National Health Service South-West Region Public Health Training scheme. FN is supported by a grant from Cancer Research UK [grant No C1345/A5809]. FEM is funded by the Medical Research Council [U.1052.00.013]. The sponsors played no part in the study design; the collection, analysis, and interpretation of data; the writing of the report; or the decision to submit the article for publication.
Competing interests: None declared.
Ethical approval: This study was approved by the Multicentre Research and Ethics Committee (MREC/01/2/91).
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