RESULTS
The flowchart is presented in Fig. 1. We identified 82421 patients with constipation and 82421 matched controls between 1999 and 2013 from the LHID. Demographic characteristics of this study participants are shown in Table 1. The constipated patients and non-constipation cohort were similar in age and gender distribution. After propensity score matching, there were no statistically significant differences between the constipation and non-constipation groups.
As shown in Table 2, the incidence of asthma was 10.8 per 1,000 person-years in the constipation group, which was higher than the rate of 5.6 per 1,000 person-years observed in the non-constipation group. After adjustment, patients with constipation had a significantly higher risk of asthma than those without constipation (aHR:1.91, 95% C.I. 1.84-1.99, p<0.001). Compared with women, men had a significantly higher risk of asthma (aHR:1.17; 95% CI, 1.12-1.22; p<0.001). In term of comorbidities, we observed that people with hypertension, COPD, or autoimmune disease had a relatively higher risk of asthma. (hypertension:1.22, 95% C.I. 1.15-1.29, p<0.001; COPD:3.21, 95% C.I. 2.94-3.50, p<0.001; autoimmune disease:1.42, 95% C.I. 1.17-1.73, p<0.001). By contrast, patients using corticosteroids or antihistamines during the study for period at least 30 days had a lower risk of asthma. (corticosteroids: 0.80, 95% C.I. 0.76-0.84, p<0.001; antihistamines: 0.61, 95% C.I. 0.59-0.64, p<0.001)
Table 3 showed that subgroup analyses were performed to assess the association between constipation and asthma based on demographic characteristics. Patients in the constipation group aged 20-39 years, had a 2.04-fold greater risk of asthma compared with the same age group in the non-constipation group (aHR; 95% CI,1.84-2.26, P < 0.001). Patients aged <20, 40-64, and ≥65 years in the constipation group had a 1.85, 1.70, and 2.02-fold greater risk of asthma.(aHR; 95% CI, 1.69-2.01, 1.57-1.83 and 1.89-2.16; P < 0.001), respectively. Among females, compared with those without constipation, there was a 1.86-fold higher risk of asthma in patients with constipation (aHR; 95% CI, 1.77-1.96; P < 0.001). Among males, there was 1.92-fold higher risk of asthma in patients with constipation (aHR; 95% CI, 1.80-2.04; P < 0.001). Furthermore, constipated patients had a higher likelihood of asthma, regardless of comorbidities and medications.
In addition, Table 4 presents that analysis for risk of asthma in constipated patients with laxatives prescription. Compared to participants without constipation, the adjusted hazard ratio was 1.76 (95% CI, 1.69-1.85; P < 0.001), 2.15(95% CI, 2.03-2.27; P < 0.001), and 2.29(95% CI, 2.10-2.49; P < 0.001) for < 3 times, 3-12 times, and ≥12 times of laxatives prescription within one year, respectively. There appeared to be a dose-effect relationship between constipation severity and risk of asthma.The Kaplan–Meier curves are shown in Fig. 2. The cumulative incidence of asthma was significantly higher in constipated patients than in non-constipated patients, and the log-rank test for the comparison of cumulative incidence curves resulted in a P-value of <0.001