| Reference | Country | Study design | Patient recruitment | Sampling frame | Definition of GORD | Definition of asthma | Method of data collection | Prevalence or incidence of asthma in individuals with GORD (%) | Prevalence or incidence of asthma in controls | OR/RR (95% CI) | |
| Unadjusted | Adjusted | ||||||||||
| El-Serag and Sonnenberg 199733 | USA | Cross-sectional | All patients in Veterans Affairs system | Administrative database | Physician-diagnosed oesophagitis or stricture | Physician diagnosis | Database review | 4314/101 366 (4.3%) | 2602/101 366 (2.6%)∗ | OR 1.5 (1.4 to 1.6) | – |
| Locke et al 199773 | USA | Cross-sectional | Random | General population | Heartburn and/or acid regurgitation at least weekly | Self-reported | Questionnaire | 35†/303 (11.6%) | 51†/642 (7.9%)‡ | OR 1.5 (1.0 to 2.4)† | OR 1.0 (0.6 to 1.3)§ |
| Ruhl et al 200174 | USA | Cohort | Random | General population administrative database | Physician-diagnosed oesophagitis or hiatal hernia | Physician diagnosis | Database review | Incidence 2.6 cases per 1000 py (10/537) | Incidence 1.0 per 1000 py|| (67/6391) | – | RR 2.1 (1.1 to 4.2)# |
| Gislason et al 200275 | Iceland, Belgium, Sweden | Cross-sectional | Random | General population | Nocturnal heartburn or belching at least weekly | Self-reported physician diagnosis | Questionnaire | 9†/101 (8.9%) | 84/2096 (4.0%)∗∗ | OR 2.3 (1.1 to 4.8)† | OR 2.2 (1.0 to 4.7)†† |
| Jaspersen et al 200376 | Germany, Austria, Switzerland | Cross-sectional | Not reported | Patients referred for endoscopy | Erosive oesophagitis on endoscopy | Self-reported (recurrent wheezing) | Questionnaire | 169/3245 (5.2%) | – | – | – |
| Khoshbaten 200327 | Iran | Cross-sectional | Random | General population | Heartburn at least 3 times in the last 2 weeks | Self-reported (asthma or wheezing) | Physician interview | 4/70 (5.7%) | – | – | – |
| Wang et al 200477 | China | Cross-sectional | Random | General population | Symptom severity and frequency score of at least 3 | Self-reported physician diagnosis | Questionnaire | 28/430 (6.5%) | 46/2102 (2.2%)‡ | OR 3.1 (1.9 to 5.0)† | – |
| Ruigomez et al 200520 | UK | Cohort study with nested case-control analysis | Random | General population administrative database | Physician diagnosis | Physician diagnosis | Database review | Incidence 6.0 cases per 1000 py (4.9–7.3) (103/5653) | Incidence 3.8 cases per 1000 py (3.1–4.6)‡‡ (99/8105) | – | RR 1.2 (0.9 to 1.6)§§ |
| Cho et al 200578 | Korea | Cross-sectional | Random | General population | Heartburn and/or acid regurgitation at least weekly | Self-reported | Questionnaire | 13†/50 (26.0%) | 39†/1205 (3.2%)‡ | OR 10.5 (5.2 to 21.3)† | OR 2.6 (1.4 to 4.8)|||| |
| Nordenstedt et al 200679 | Norway | Cross-sectional | Random | General population | Severe heartburn and/or acid regurgitation | Self-reported | Questionnaire | 420/3153 (13.3%) | 2940/40210 (7.3%)‡ | OR 1.9 (1.7 to 2.2)† | OR 1.6 (1.4 to 1.9)## |
| Rey et al 200680 | Spain | Cross-sectional | Random | General population | Heartburn and/or acid regurgitation at least weekly | Self-reported | Questionnaire | 30†/245 (12.2%) | 91†/1709 (5.3%)‡ | OR 2.5 (1.6 to 3.8)† | OR 1.0 (0.7 to 1.5)∗∗∗ |
CI, Confidence interval; GORD, gastro-oesophageal reflux disease; OR, odds ratio; py, person-years; RR, relative risk.
∗Controls were patients without a diagnosis of oesophagitis or oesophageal stricture.
†Calculated based on values given in publication.
‡Controls were individuals from the general population who had no symptoms of GORD.
§Adjusted for age, sex, psychosomatic symptom score and each of the remaining atypical symptoms.
||Controls were individuals from the general population without hiatal hernia, oesophagitis, asthma, chronic bronchitis, emphysema or chronic cough at baseline.
#Adjusted for age, sex, marital status, education, body mass index, physical activity, smoking and diabetes.
∗∗Controls were individuals from the general population without nocturnal symptoms of GORD.
††Adjusted for possible confounders.
‡‡Controls were age and sex-matched primary care patients without a diagnosis of asthma or GORD at baseline.
§§Adjusted for age, sex, smoking, previous morbidity and healthcare utilisation.
||||Adjusted for age, sex and remaining atypical symptoms.
##Adjusted for age, sex, body mass index, smoking and use of asthma medication.
∗∗∗Adjusted for age, sex, coffee consumption, alcohol consumption, smoking, psychosomatic symptom score and all other atypical symptoms.