The risk of asthma in rheumatoid arthritis: a population-based cohort study.
BACKGROUND
Several studies discussed the relations between asthma and rheumatoid arthritis (RA) but the results were controversial. These studies were either questionnaire based or with small study populations. We aimed to examine the risk of asthma among RA patients in a nationwide population.


METHODS
We conducted a cohort study using data from the National Health Insurance system of Taiwan. The RA cohort included 27 602 patients who were newly diagnosed and recruited between 1998 and 2008. Each patient was randomly frequency-matched with three people without RA on age group, sex and the year of index date from the general population. The occurrence of asthma was followed up until the end of 2010. The relative risks of asthma were estimated using Cox proportional hazard models after adjusting for age and comorbidities.


RESULTS
The overall incidence rate of asthma was 2.07-fold greater in the RA cohort than in the non-RA cohort (4.56 vs. 2.22 per 1000 person-years, 95% CI = 1.99-2.15). Stratified analyses by gender, age group and comorbidity revealed that the risk of asthma associated with RA was higher in females (adjusted hazard ratio (HR) = 2.18, 95% CI = 1.97-2.41), individuals younger than 40 years old (adjusted HR = 3.26, 95% CI = 2.09-5.11) and without comorbidity (adjusted HR = 2.17, 95% CI = 1.97-2.39).


CONCLUSIONS
Patients with RA had a significantly higher risk of developing asthma than healthy people in all sex and age subgroups. Stratified analyses indicated that there was a higher risk in women with RA than in men with RA when compared to their counterpart. Similarly, the HR of asthma associated with RA was higher in younger subjects, although the incidence rate increased with age.
From the Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, China Medical University Hospital and China Medical University, Taichung 404, Taiwan, Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Chu Shang Show Chwan Hospital, Nantou 557, Taiwan, Department of Public Health, China Medical University, Taichung 404, Taiwan, Management Office for Health Data, China Medical University Hospital, Taichung 404, Taiwan, Division of Nephrology, Department of Pediatrics, China Medical University Hospital and China Medical University, Taichung 404, Taiwan and Institute of Biostatistics, China Medical University, Taichung 404, TaiwanFrom the Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, China Medical University Hospital and China Medical University, Taichung 404, Taiwan, Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Chu Shang Show Chwan Hospital, Nantou 557, Taiwan, Department of Public Health, China Medical University, Taichung 404, Taiwan, Management Office for Health Data, China Medical University Hospital, Taichung 404, Taiwan, Division of Nephrology, Department of Pediatrics, China Medical University Hospital and China Medical University, Taichung 404, Taiwan and Institute of Biostatistics, China Medical University, Taichung 404, Taiwan.
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Shen
From the Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, China Medical University Hospital and China Medical University, Taichung 404, Taiwan, Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Chu Shang Show Chwan Hospital, Nantou 557, Taiwan, Department of Public Health, China Medical University, Taichung 404, Taiwan, Management Office for Health Data, China Medical University Hospital, Taichung 404, Taiwan, Division of Nephrology, Department of Pediatrics, China Medical University Hospital and China Medical University, Taichung 404, Taiwan and Institute of Biostatistics, China Medical University, Taichung 404, TaiwanFrom the Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, China Medical University Hospital and China Medical University, Taichung 404, Taiwan, Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Chu Shang Show Chwan Hospital, Nantou 557, Taiwan, Department of Public Health, China Medical University, Taichung 404, Taiwan, Management Office for Health Data, China Medical University Hospital, Taichung 404, Taiwan, Division of Nephrology, Department of Pediatrics, China Medical University Hospital and China Medical University, Taichung 404, Taiwan and Institute of Biostatistics, China Medical University, Taichung 404, Taiwan.
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Lin
From the Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, China Medical University Hospital and China Medical University, Taichung 404, Taiwan, Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Chu Shang Show Chwan Hospital, Nantou 557, Taiwan, Department of Public Health, China Medical University, Taichung 404, Taiwan, Management Office for Health Data, China Medical University Hospital, Taichung 404, Taiwan, Division of Nephrology, Department of Pediatrics, China Medical University Hospital and China Medical University, Taichung 404, Taiwan and Institute of Biostatistics, China Medical University, Taichung 404, Taiwan.
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Wei
From the Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, China Medical University Hospital and China Medical University, Taichung 404, Taiwan, Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Chu Shang Show Chwan Hospital, Nantou 557, Taiwan, Department of Public Health, China Medical University, Taichung 404, Taiwan, Management Office for Health Data, China Medical University Hospital, Taichung 404, Taiwan, Division of Nephrology, Department of Pediatrics, China Medical University Hospital and China Medical University, Taichung 404, Taiwan and Institute of Biostatistics, China Medical University, Taichung 404, Taiwan.
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Tu
From the Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, China Medical University Hospital and China Medical University, Taichung 404, Taiwan, Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Chu Shang Show Chwan Hospital, Nantou 557, Taiwan, Department of Public Health, China Medical University, Taichung 404, Taiwan, Management Office for Health Data, China Medical University Hospital, Taichung 404, Taiwan, Division of Nephrology, Department of Pediatrics, China Medical University Hospital and China Medical University, Taichung 404, Taiwan and Institute of Biostatistics, China Medical University, Taichung 404, Taiwan yufenli@mail.cmu.edu.tw.
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YF
Li
D000328:Adult; D017677:Age Distribution; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000150:complications* / Q000453:epidemiology; D001249:Asthma / Q000453:epidemiology / Q000209:etiology*; D015331:Cohort Studies; D015897:Comorbidity; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D018570:Risk Assessment / Q000379:methods; D017678:Sex Distribution; D013624:Taiwan / Q000453:epidemiology; D055815:Young Adult