INTRODUCTION
Among respiratory diseases, asthma is one of the most burdensome disorder both affects in childhood and adulthood. The prevalence was estimated that there were more than 272 million people had asthma worldwide in 2017.[1] Asthma not only increases financial, social, and psychological burdens, but also makes a harmful impact on quality of life, and is connected with comorbidities.[2] Interestingly, there is increasing evidence presenting an connection between asthma and constipation[3], a common condition affecting adults and children globally and a frequent reason for visits to physicians. The mean global prevalence of constipation in children is 12% and that in adult is 16%. [4] Even though constipation has few complications of life-threatening, it can make physical and mental distress for patients and their families, eventually impairing quality of life. Complications of constipation included hemorrhoids, rectal prolapse, and fecal or urine incontinence, which usually increases the frequency of hospitalizations or outpatient department visits, leading to increased burdens of health insurance.
Nowadays, constipation is seemed to be a causative factor in intestinal dysbiosis[5] and therapeutic managements are increasingly incorporating prebiotics, probiotics[6], or synbiotics with a view to regulating the intestinal microflora[7, 8]. Moreover, recent research has demonstrated that the gut microbiota would exert important regulatory effects via the gut-lung axis.[9-11] For instance, gut dysbiosis[12] and lower concentration of short-chain fatty acids (SCFAs) in the bowel are found in patients with asthma. This condition decreases the production of butyrate and propionate, leading to the dysregulation of gut inflammation and the defect of the intestinal epithelial barriers, resulting in leaky gut and allow penetration of microorganisms and toxins into systemic circulation, thereby activating Th2 immune responses, eventually contributing to airway inflammation. Some research have suggested that allergic diseases might be associated with constipation.[13, 14] Furthermore, previous study has demonstrated that stool stasis in the long time could influence the microbiota and environment of gut, resulting in deleterious effects on mucosal immunity and intestinal motility.[15] Whether if constipation predisposes susceptible people to asthma is unknown. At present, there are still scanty data on the connection between constipation and asthma in the literature. In addition, this association has never been investigated using a large-scale national longitudinal database. We hypothesized that constipation might influence the risk of asthma and assessed this hypothesis by analyzing a real-world, population-based retrospective cohort from National Health Insurance Research Database (NHIRD) in Taiwan.