INTRODUCTION
Atopic dermatitis (AD) is a long-lasting, relapsing pruritic
inflammatory skin disorder that occurs in both childhood and adulthood.
It leads to a defective skin barrier and strengthened T-cell responses
to allergens and microbes from surroundings, resulting in chronic
inflammatory reaction.1 In the past few years, the
prevalence of atopic dermatitis has increased rapidly in developed
countries such as the United States2 and in
Taiwan.3 AD not only increases social, financial, and
psychological burdens4, but also makes a deleterious
effect on quality of life, 5 and is associated with
comorbidities.6
Interestingly, there is growing evidence showing an association between
AD and constipation, a common condition affecting children and adults
worldwide and a frequent reason for visits to gastroenterologists. The
mean global prevalence of constipation in adults is 16% and that in
children is 12%.7 Although constipation has few
life-threatening complications, it can affect physical and emotional
distress for patients and their family members, eventually impairing
quality of life. Complications of constipation included hemorrhoids,
fecal incontinence, and rectal prolapse, which often increases the
frequency of outpatient department visits or hospitalizations, resulting
in increased cost of health insurance.
Constipation is now considered to be a causative factor in gut
dysbiosis8 and therapeutic approaches are increasingly
incorporating probiotics, prebiotics, or synbiotics with a view to
manipulating the intestinal microbiota.9 In addition,
recent study has demonstrated that the gut microbiota might exert
important regulatory effects via the gut-skin axis.10For example, intestinal dysbiosis and lower concentration of short-chain
fatty acids (SCFAs) in the bowel are found in patients with
AD.11–14 In a Korean study, which investigated the
gut microbiome and relevant metabolites in patients with AD, dysbiosis
of Faecalibacterium prausnitzii was observed in stool samples of
patients with AD. This condition decreases the production of propionate
and butyrate, resulting in the dysregulation of intestinal inflammation
and the defect of the epithelial barrier (leaky gut), thereby allowing
penetration of toxin and microbes into systemic circulation, which
activates Th2 immune responses, eventually culminating in skin
damage.12 Some researches have suggested that allergic
disease might be connected with constipation.15,16Furthermore, previous research has indicated that prolonged stool stasis
may change the intestinal environment and microbiota, resulting in
deleterious effects on gut motility and mucosal
immunity.17,18 Whether constipation predisposes
susceptible individuals to AD is unknown. Currently, there are scanty
data on the association between constipation and AD in the literature.
Moreover, this relationship has never been investigated by data obtained
from the large national longitudinal database. We hypothesized that
constipation could impact the risk of AD and evaluated this hypothesis
by analyzing the population-based retrospective cohort from Taiwanese
National Health Insurance Research Database (NHIRD).