ORIGINAL ARTICLE EPIDEMIOLOGY AND GENETICS A meta-analysis on wood dust exposure and risk of asthma M. Pe ´rez-Rı´os 1,2,3 , A. Ruano-Ravina 1,2,4 , M. Etminan 5 & B. Takkouche 1,2 1 Department of Preventive Medicine, University of Santiago de Compostela, 15782 Santiago de Compostela; 2 CIBER de Epidemiologı ´a y Salud Pu ´ blica, CIBERESP; 3 Epidemiology Section, Department of Public Health, Galician Regional Authority; 4 Galician Agency for Health Technology Assessment, Galician Department of Health, Spain; 5 Center for Clinical Epidemiology and Evaluation and Department of Medicine, University of British Columbia, Vancouver, BC, Canada To cite this article: Pe ´ rez-Rı ´os M, Ruano-Ravina A, Etminan M, Takkouche B. A meta-analysis on wood dust exposure and risk of asthma. Allergy 2010; 65: 467–473. Asthma is a chronic inflammatory condition that represents an important health problem in the developed world. It is the most common occupational respiratory disorder in the indus- trialized countries. Approximately, 250 specific substances at work are associated with the disease and about one-fifth of asthma cases is related to occupation (1). Recent data in the US show that the estimated number of workers potentially exposed to occupational triggers of asthma ranges from 8 to 20 million, which represent about 24% of the workforce, while the prevalence of the disease in the employed popula- tion is 6.5% (2). Wood workers include different occupations such as car- penters, small boat constructors or sawmill workers, all of which are exposed to a certain amount of wood dust. They represent an important occupational group with more than one million people employed in Europe (3) and 370 000 in the US, a figure that will grow 3% through 2016 (4). An increased risk of asthma among wood workers would then cause an important public health concern given the large number of people employed in this sector. The biological mechanism responsible for the effect of wood dust is not fully elucidated (5). Some studies have shown that abietic acid contained in the resin of some trees may induce lytic damage to the bronchial epithelial cells (6). Further, terpenes contained in pine and other coniferous trees may cause increase bronchial responsiveness (7). IgE medi- ated sensitization is another plausible mechanism (8). To date, results of epidemiologic studies have been incon- sistent. Although several studies found an increase in the risk of asthma among wood workers, other studies failed to find any association (5, 9). So far, no comprehensive meta-analysis is available. We, therefore, summarized the scientific evidence and carried out a meta-analysis on occupational exposure to wood dust and risk of asthma, following the MOOSE guidelines for meta- analyses of observational studies (10). Our study is limited to asthma occurring in an occupational setting. Methods Data sources and searches We conducted a computerized Medline search from 1966 to August 2008 to identify potentially eligible studies. We applied the following algorithm both in Medical Subject Heading and in free text words: (ASTHMA) AND (WOOD*) AND Keywords asthma; ethnicity; meta-analysis; wood; work. Correspondence Mo ´ nica Pe ´ rez-Rı ´os, Department of Preventive Medicine, University of Santiago de Compostela, 15782 Santiago de Compostela, Spain. Accepted for publication 13 July 2009 DOI:10.1111/j.1398-9995.2009.02166.x Edited by: Marc Humbert Abstract Work-related asthma is the most common occupational respiratory disorder in the industrialized countries. It has been postulated that wood dust exposure may increase the risk of work-related asthma. The objective of this study was to assess, through a meta-analysis, the risk of developing work-related asthma associated with wood dust exposure. A systematic search of the literature was performed. Inclusion and exclusion criteria were applied and a quality scale used to measure the quality of the included studies was developed. Using standard meta-analysis techniques, studies were pooled using both random and fixed effects models. Nineteen studies were included which consisted of three cohort studies, twelve case–control studies and four mortality studies. The pooled relative risk (RR) of asthma among workers exposed to wood dust was 1.53 (95% CI 1.25–1.87). When the analysis was restricted to studies carried out on Caucasian populations, the pooled RR was 1.59 (95% CI 1.26–2.00) while the pooled RR of studies on Asian populations was 1.15 (95% CI 0.92–1.44). Wood workers present a higher risk of asthma. Future research should include careful evaluation of ethnicity and nativity as risk modifiers. Allergy Allergy 65 (2010) 467–473 ª 2009 John Wiley & Sons A/S 467