title: Why do thin people have elevated all-cause mortality? Evidence on confounding and reverse causality in the association of adiposity and COPD from the British Women's Heart and Health Study.
abstract: Low adiposity has been linked to elevated mortality from several causes including respiratory disease. However, this could arise from confounding or reverse causality. We explore the association between two measures of adiposity (BMI and WHR) with COPD in the British Women's Heart and Health Study including a detailed assessment of the potential for confounding and reverse causality for each adiposity measure. Low BMI was found to be associated with increased COPD risk while low WHR was not (OR = 2.2; 95% CI 1.3-3.1 versus OR = 1.2; 95% CI 0.7-1.6). Potential confounding variables (e.g. smoking) and markers of ill-health (e.g. unintentional weight loss) were found to be higher in low BMI but not in low WHR. Women with low BMI have a detrimental profile across a broad range of health markers compared to women with low WHR, and women with low WHR do not appear to have an elevated COPD risk, lending support to the hypothesis that WHR is a less confounded measure of adiposity than BMI. Low adiposity does not in itself appear to increase the risk of respiratory disease, and the apparent adverse consequences of low BMI may be due to reverse causation and confounding.
authors.affiliation: Department of Non-communicable Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, United Kingdom.
authors.forename: Caroline
authors.initials: C
authors.lastname: Dale
authors.affiliation: Department of Non-communicable Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, United Kingdom.
authors.forename: Eveline
authors.initials: E
authors.lastname: Nüesch
authors.affiliation: Department of Non-communicable Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Prieto-Merino
authors.affiliation: Department of Non-communicable Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, United Kingdom.
authors.forename: Minkyoung
authors.initials: M
authors.lastname: Choi
authors.affiliation: Department of Non-communicable Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, United Kingdom.
authors.forename: Antoinette
authors.initials: A
authors.lastname: Amuzu
authors.affiliation: Department of Non-communicable Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, United Kingdom.
authors.forename: Shah
authors.initials: S
authors.lastname: Ebrahim
authors.affiliation: Department of Non-communicable Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, United Kingdom; Institute of Cardiovascular Science, University College London, London, United Kingdom.
authors.forename: Juan P
authors.initials: JP
authors.lastname: Casas
authors.affiliation: CAiTE centre, School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom.
authors.forename: George
authors.initials: G
authors.lastname: Davey-Smith
mesh_terms: D050154:Adiposity / Q000502:physiology*; D000368:Aged; D015992:Body Mass Index; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008019:Life Style; D008875:Middle Aged; D009765:Obesity / Q000150:complications / Q000175:diagnosis*; D016017:Odds Ratio; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications* / Q000401:mortality; D012307:Risk Factors; D012907:Smoking; D011795:Surveys and Questionnaires; D006113:United Kingdom; D049629:Waist-Hip Ratio