Type 1 diabetes and asthma: a systematic review and meta-analysis of observational studies

Purpose: Type 1 diabetes (T1D) and asthma are both the top concurrent non-communicable diseases in the world, and the existence of a relationship between the two is an area of debate. Methods: All eligible observational studies in PubMed and EMBASE databases from inception to August 2021 were searched for data extraction and analysis. The pooled odds ratio (OR) with corresponding 95% confidence intervals (95% CI) was evaluated using fixed-effects or random-effects models in RevMan 5.3, and I²and Cochran Q tests were used to assess the heterogeneity. Results: 22 studies with 25,578 T1D and 3,330,901 non-T1D were included in this meta‐analysis. After data analysis, there seems to be no apparent connectivity between asthma and T1D as the crude OR (cOR) was 1.07 (95%CI, 0.93–1.23). Nevertheless, after limiting the meta-analysis to 6 studies with adjusted OR (aOR) available, the results suggested a positive association between T1D and asthma (aOR, 1.15; 95%CI, 1.06–1.25). Corresponding with this, a meta-analysis of cohort studies also found a positive association between T1D and asthma with the pooled cOR of 1.27 (95% CI, 1.09–1.49) and aOR of 1.15 (95%CI, 1.05–1.26). Further analysis of 7 studies in which the diagnosis of asthma precedes T1D onset revealed that asthma patients are at increased risk of subsequent T1D with the pooled cOR of 1.23 (95%CI, 1.04–1.44) and aOR of 1.58 (95% CI, 1.11–2.24). Conclusion: Our meta-analysis suggests a possible association between T1D and asthma, and patients who were previously diagnosed with asthma carried higher odds of developing T1D.