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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.

Dale C, Nüesch E, Prieto-Merino D, Choi M, Amuzu A, Ebrahim S, Casas JP, Davey-Smith G - PLoS ONE (2015)

Bottom Line: However, this could arise from confounding or reverse causality.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Non-communicable Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, United Kingdom.

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.

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(A) Prevalence of COPD and symptoms of lung function by categories of BMI and WHR (lowest to highest).(B) Prevalence of smoking measures by categories of BMI and WHR (lowest to highest). (C) Prevalence of markers of ill-health by categories of BMI and WHR (lowest to highest).
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pone.0115446.g001: (A) Prevalence of COPD and symptoms of lung function by categories of BMI and WHR (lowest to highest).(B) Prevalence of smoking measures by categories of BMI and WHR (lowest to highest). (C) Prevalence of markers of ill-health by categories of BMI and WHR (lowest to highest).

Mentions: For some measures, there was evidence for a difference in prevalence in the lowest BMI and WHR exposure categories (COPD, dyspnea symptoms, % never smoked and unintended weight loss) (Fig 1, S5 Table, S6 Table and S7 Table). COPD prevalence was higher amongst those with the lowest BMI compared to those with lowest WHR (15.2%; 95% CI 9.8–20.6 amongst those with a WHR<0.72 compared to 33.6%; 95% CI 26.1–41.1 amongst those with a BMI < 22kg/m2) (Fig 1A). Results for dyspnea symptoms were consistent with this.


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.

Dale C, Nüesch E, Prieto-Merino D, Choi M, Amuzu A, Ebrahim S, Casas JP, Davey-Smith G - PLoS ONE (2015)

(A) Prevalence of COPD and symptoms of lung function by categories of BMI and WHR (lowest to highest).(B) Prevalence of smoking measures by categories of BMI and WHR (lowest to highest). (C) Prevalence of markers of ill-health by categories of BMI and WHR (lowest to highest).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4401726&req=5

pone.0115446.g001: (A) Prevalence of COPD and symptoms of lung function by categories of BMI and WHR (lowest to highest).(B) Prevalence of smoking measures by categories of BMI and WHR (lowest to highest). (C) Prevalence of markers of ill-health by categories of BMI and WHR (lowest to highest).
Mentions: For some measures, there was evidence for a difference in prevalence in the lowest BMI and WHR exposure categories (COPD, dyspnea symptoms, % never smoked and unintended weight loss) (Fig 1, S5 Table, S6 Table and S7 Table). COPD prevalence was higher amongst those with the lowest BMI compared to those with lowest WHR (15.2%; 95% CI 9.8–20.6 amongst those with a WHR<0.72 compared to 33.6%; 95% CI 26.1–41.1 amongst those with a BMI < 22kg/m2) (Fig 1A). Results for dyspnea symptoms were consistent with this.

Bottom Line: However, this could arise from confounding or reverse causality.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Non-communicable Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, United Kingdom.

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.

Show MeSH
Related in: MedlinePlus