Introduction
The incidence of allergic diseases has recently increased in different
regions around the world.1 In Japan, allergic diseases
are a serious health concern, with high rates of wheezing (16.4%),
asthma (10.5%), and atopic dermatitis (21.5%) observed in children at
5 years of age.2 Concurrently, cesarean delivery rates
have been increasing worldwide,3–5 and have
approximately doubled in Japan since 1990, reaching 18.6% in
2014.6 The increased rate is mainly due to a rise in
elective cesarean delivery. Some recent reports describe associations
between cesarean delivery and allergic diseases.7-9Given that the increases in allergic disease rates have occurred over a
short period of time, they may be associated with environmental factors
rather than genetic factors. Compared with children born by vaginal
delivery, those born by cesarean delivery have different gut flora and
cytokine profiles,10–12 which are thought to be
related to allergic diseases. In contrast, some reports showed that
delivery by cesarean section was not associated with the development of
allergic diseases.13-15 Therefore, the association
between cesarean delivery and allergic diseases is controversial. In
this study, we investigated the association between infants born by
cesarean delivery and the development of asthma, atopic dermatitis,
wheezing, and eczema using data from a large sample size cohort study of
the Japan Environment and Children’s Study (JECS).