Obesity Comorbidity Body mass index and risk of pneumonia: a systematic review and meta-analysis D. T. Phung 1 , Z. Wang 2 , S. Rutherford 1 , C. Huang 1 and C. Chu 1 1 Centre for Environment and Population Health, Griffith University, Brisbane, Queensland, Australia; 2 Centre for Chronic Disease, School of Medicine, University of Queensland, Brisbane, Queensland, Australia Received 5 May 2013; revised 27 May 2013; accepted 28 May 2013 Address for correspondence: Dr DT Phung, Centre for Environment and Population Health, Griffith University, 170 Kessel Road, Nathan, Brisbane, QLD 4111, Australia. E-mail: d.phung@griffith.edu.au Summary The aims of our meta-analysis were to examine the pattern and gender’s influence on body mass index (BMI) – pneumonia relationship. Published studies were searched from PubMed, Web of Science, Cochrane Library databases using key- words of pneumonia, BMI and epidemiologic studies. Random-effects analysis was applied to estimate pooled effect sizes from individual studies. The Cochrane Q-test and index of heterogeneity (I 2 ) were used to evaluate heterogeneity, and Egger’s test was used to evaluate publication bias. Random-effects meta- regression was applied to examine the pattern and gender’s influence on BMI– pneumonia relationship. A total of 1,531 studies were initially identified, and 25 studies finally were included. The pooled relative risk (RR) and meta-regression model revealed a J-shaped relationship between BMI and risk of community-acquired pneumonia (underweight, RR 1.8, 95% confidence interval [CI], 1.4–2.2, P < 0.01; over- weight, 0.89, 95%CI, 0.8–1.03, P, 0.1; obesity, 1.03, 95% CI, 0.8–1.3, p. 8) and U-shaped relationship between BMI and risk of influenza-related pneumonia (underweight, RR 1.9, 95% CI, 1.2–3, P < 0.01; overweight, 0.89, 95% CI, 0.79–0.99, P, 0.03; obesity, 1.3, 95% CI, 1.05–1.63, p. 2; morbidity obesity, 4.6, 95% CI, 2.2–9.8, P < 0.01); whereas, no difference in risk of nosocomial pneu- monia was found across the BMI groups. Gender difference did not make signifi- cant contribution in modifying BMI–pneumonia risk relationship. Keywords: BMI, body mass index, meta-analysis, pneumonia. obesity reviews (2013) Introduction Pneumonia is a substantial public health problem as it contributes significantly to morbidity, mortality and cost. It has been ranked as the third leading cause of death world- wide (1) and is one of the most common infectious disease in Western societies (2). A previous survey indicated that hospitalizations with pneumonia elevated by 20–50% during the past decade (3–5). The estimated annual inci- dence of pneumonia ranged from 1.6 to 11.6 per 1,000 inhabitants (6,7). The incidence of pneumonia is found highest among the elderly and persons who have coexisting illness (8) and the mortality rate of this disease remains high regardless of improvements in diagnostic and treat- ment techniques (9–11). It has been believed that obesity can be a risk factor of respiratory tract infections, including pneumonia because of impaired T- and B–cell-medicated immune response, a higher risk of aspiration, reduced lung volume, and altered ventilation pattern (12,13). In addition, obesity is also asso- ciated with the risk of major chronic diseases such as dia- betes, cardiovascular diseases, asthma, cancer, and liver obesity reviews doi: 10.1111/obr.12055 1 © 2013 The Authors obesity reviews © 2013 International Association for the Study of Obesity