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      BMI–mortality association: shape independent of smoking status but different for chronic lung disease and lung cancer

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          Abstract

          Background

          Besides smoking, low or high body mass index (BMI) is associated with chronic lung disease (CLD). It is unclear how CLD is associated with BMI, whether smoking interacts with this association, and how the associations differ from the patterns known for lung cancer.

          Population and Methods

          Our population comprised 35,212 individuals aged 14–99, who participated in population-based surveys conducted in 1977–1993 in Switzerland (mortality follow-up until 2014). We categorized smokers into never, former, light, and heavy; and BMI into underweight, normal weight, overweight, and obese. Hazard ratios (HRs) were obtained with multivariable Cox proportional hazards models.

          Results

          CLD mortality was strongly associated with being underweight. This was mainly due to the effect in men (HR 5.04 [2.63–9.66]) and also prevailed in never smokers (HR 1.81 [1.11–3.00]). Obesity was also associated with CLD mortality (HR men: 1.37 [1.01–1.86], women: 1.39 [0.90–2.17]), but not with lung cancer mortality. In line with lung cancer, for CLD, the BMI–mortality association followed the same shape in all smoking categories, suggesting that this association was largely independent of smoking status.

          Conclusion

          The shape of the BMI–mortality association was inversely linear for lung cancer but followed a U-shape for CLD. Further research should examine the potentially protective effect of obesity on lung cancer occurrence and the possibly hazardous impact of underweight on CLD development.

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          Most cited references 13

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          Body Mass Index and Mortality in Chronic Obstructive Pulmonary Disease: A Meta-Analysis

          Background The association between body mass index (BMI) and mortality in patients suffering from chronic obstructive pulmonary disease (COPD) has been a subject of interest for decades. However, the evidence is inadequate to draw robust conclusions because some studies were generally small or with a short follow-up. Methods We carried out a search in MEDLINE, Cochrane Central Register of Controlled Trials, and EMBASE database for relevant studies. Relative risks (RRs) with 95% confidence interval (CI) were calculated to assess the association between BMI and mortality in patients with COPD. In addition, a baseline risk-adjusted analysis was performed to investigate the strength of this association. Results 22 studies comprising 21,150 participants were included in this analysis. Compared with patients having a normal BMI, underweight individuals were associated with higher mortality (RR  = 1.34, 95% CI  = 1.01–1.78), whereas overweight (RR  = 0.47, 95% CI  = 0.33–0.68) and obese (RR  = 0.59, 95% CI  = 0.38–0.91) patients were associated with lower mortality. We further performed a baseline risk-adjusted analysis and obtained statistically similar results. Conclusion Our study showed that for patients with COPD being overweight or obese had a protective effect against mortality. However, the relationship between BMI and mortality in different classes of obesity needed further clarification in well-designed clinical studies.
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            Prevalence of airflow obstruction in smokers and never-smokers in Switzerland.

            The aim of the present study was to measure age-specific prevalence of airflow obstruction in Switzerland in smokers and never-smokers using pulmonary function tests and respiratory symptoms from 6,126 subjects participating in the Swiss Cohort Study on Air Pollution and Lung Diseases in Adults. The lower limit of normal of the forced expiratory volume in 1 s/forced vital capacity ratio was used to define airflow obstruction. Severity of airflow obstruction was graded according to the recommendations of the Global Initiative for Chronic Obstructive Lung Disease. Prevalence of airflow obstruction ranged from 2.5% in subjects aged 30-39 yrs to 8.0% in those aged ≥ 70 yrs. In multivariate analysis, age (OR 2.8, ≥ 70 yrs versus 30-39 yrs), smoking (OR 1.8) and asthma (OR 6.7) were associated with airflow obstruction. Never-smokers constituted 29.3% of subjects with airflow obstruction. Never-smokers with airflow obstruction were younger, more likely to be male and reported asthma more frequently than obstructive smokers. Obstructive smokers and never-smokers had similar level of symptoms and quality of life impairment. The prevalence of airflow obstruction in Switzerland is similar to other developed countries. Never-smokers account for a third of the prevalence, which is higher proportion than elsewhere. Airflow obstruction in never-smokers deserves attention because of its frequency and its similar health impact to that in smokers.
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              Body mass index and risk of lung cancer among never, former, and current smokers.

              Although obesity has been directly linked to the development of many cancers, many epidemiological studies have found that body mass index (BMI)--a surrogate marker of obesity--is inversely associated with the risk of lung cancer. These studies are difficult to interpret because of potential confounding by cigarette smoking, a major risk factor for lung cancer that is associated with lower BMI. We prospectively examined the association between BMI and the risk of lung cancer among 448 732 men and women aged 50-71 years who were recruited during 1995-1996 for the National Institutes of Health-AARP Diet and Health Study. BMI was calculated based on the participant's self-reported height and weight on the baseline questionnaire. We identified 9437 incident lung carcinomas (including 415 in never smokers) during a mean follow-up of 9.7 years through 2006. Multivariable Cox proportional hazards regression models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) with adjustment for lung cancer risk factors, including smoking status. To address potential bias due to preexisting undiagnosed disease, we excluded potentially unhealthy participants in sensitivity analyses. All statistical tests were two-sided. The crude incidence rate of lung cancer over the study follow-up period was 233 per 100 000 person-years among men and 192 per 100 000 person-years among women. BMI was inversely associated with the risk of lung cancer among both men and women (BMI ≥35 vs 22.5-24.99 kg/m(2): HR = 0.81, 95% CI = 0.70 to 0.94 and HR = 0.73, 95% CI = 0.61 to 0.87, respectively). The inverse association was restricted to current and former smokers and was stronger after adjustment for smoking. Among smokers, the inverse association persisted even after finely stratifying on smoking status, time since quitting smoking, and number of cigarettes smoked per day. Sensitivity analyses did not support the possibility that the inverse association was due to prevalent undiagnosed disease. Our results suggest that a higher BMI is associated with a reduced risk of lung cancer in current and former smokers. Our inability to attribute the inverse association between BMI and the risk of lung cancer to residual confounding by smoking or to bias suggests the need for considering other explanations.
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                Author and article information

                Journal
                Int J Chron Obstruct Pulmon Dis
                Int J Chron Obstruct Pulmon Dis
                International Journal of COPD
                International Journal of Chronic Obstructive Pulmonary Disease
                Dove Medical Press
                1176-9106
                1178-2005
                2018
                06 June 2018
                : 13
                : 1851-1855
                Affiliations
                [1 ]Epidemiology, Biostatistics and Prevention Institute (EBPI), University of Zurich, Zurich, Switzerland
                [2 ]Health Department – Nutrition and Dietetics, Bern University of Applied Sciences, Bern, Switzerland
                Author notes
                Correspondence: Matthias Bopp, Epidemiology, Biostatistics and Prevention Institute (EBPI), University of Zurich, Hirschengraben 84, 8001 Zurich, Switzerland, Tel +41 44 634 4614, Fax +41 44 634 4986, Email matthias.bopp@ 123456uzh.ch
                Article
                copd-13-1851
                10.2147/COPD.S157629
                5995287
                © 2018 Faeh et al. This work is published and licensed by Dove Medical Press Limited

                The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.

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                Original Research

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