Seasonality in Flares and Months of Births of Patients
with Ulcerative Colitis in a Chinese Population
Aiping Bai Æ Æ Yuan Guo Æ Æ Yuhuan Shen Æ Æ Yong Xie Æ Æ
Xuan Zhu Æ Æ Nonghua Lu
Received: 4 June 2008/Accepted: 16 July 2008/Published online: 3 December 2008
? The Author(s) 2008. This article is published with open access at Springerlink.com
in flares or months of births of inflammatory bowel disease
patients have been inconsistent, but little data are available
in a Chinese population. The aim of this study was to
determine whether symptom flares and births of ulcerative
colitis (UC) patients follow a seasonal pattern. Methods
Patients with a diagnosis of UC established between Jan-
uary 1990 and December 2007 were investigated according
to the occurrence of flares of symptoms and months of
births. The expected flares or births were calculated on a
monthly basis over the study period, taking into consider-
ation the difference in the number of days in the month in
each year. Results A total of 409 UC patients were included
in the study, and 1030 flares of symptoms were determined.
The peak number of flares occurred during the spring and
summer, especially in June, while the nadir occurred in the
P\0.005). The symptom flares also occurred more fre-
quently in the spring–summer period than in the autumn–
winter period (v2(3 df)= 22.1269, P\0.001). There was
no statistical difference in birth distribution on a monthly
Background and Aims Reports on seasonality
or seasonal (spring, summer, autumn, winter) basis. How-
ever, the births of UC patients occurred more frequently in
the autumn–winter period than in the spring–summer per-
iod when the data were merged into these two seasonal
components (v2(1 df)= 5.255607, P\0.025). Conclusions
The data indicate that the symptom flares of UC occurred
more frequently in the spring and summer, while the births
of UC patients occurred more often in the autumn and
winter. Environmental recurring factors may be associated
with the symptom flares of UC, and these factors during
pregnancy or postpartum may be associated with suscep-
tibility to UC later in life.
Environmental factor ? Seasonality ?
The relationship between environmental factors and out-
breaks of various diseases has been of interest to medical
practitioners for a long time. Environmental factors are
believed to trigger the onset of some diseases in genetically
susceptible individuals and to play a significant role in the
inflammatory response of these diseases [1–3]. Environ-
mental factors demonstrate seasonal fluctuations and
facilitate the pathogenesis of such diseases as peptic
ulceration , asthma , and chronic heart failure .
Ulcerative colitis (UC) and Crohn’s disease (CD) are
collectively referred to as inflammatory bowel disease
(IBD) and are both chronic relapsing diseases characterized
by alternating periods of remission and active disease. It is
currently believed that altered immunological function,
resulting from an abnormal interplay between genetic
susceptibility and environmental factors, significantly
A. Bai (&) ? Y. Xie ? X. Zhu ? N. Lu
Department of Gastroenterology, The First Affiliated Hospital of
Nanchang University, Nanchang 330006, China
Department of Pharmacy, The First Affiliated Hospital of
Nanchang University, Nanchang 330006, China
Department of Gastroenterology, The People’s Hospital of
Yicheng, Yicheng 441400, China
Dig Dis Sci (2009) 54:1094–1098
contributes to the mucosal inflammation of the intestinal
tract . To date, the environmental factors that contribute
to the course of IBD have not been well defined, and while
the results of some studies suggest that there may be sea-
sonal variation in the natural history of IBD [5–8] as well
as seasonality in month of birth of the patients [9, 10],
those of other studies do not reveal any such relationship
[11–13]. All of these results, however, were based on data
obtained from studies carried out in Western (=‘‘devel-
To date, little data on the seasonality of flares in terms of
patterns of IBD symptoms and month of births of IBD
patients are available in Asian populations, especially the
Chinese population. The incidence of IBD has been
increasing in China in recent years. However, Chinese
patients show somewhat different clinical patterns of IBD
from those of their Western counterparts, such as a lower
manifestation of fistulae and perianal diseases and a lower
incidence of family history , which may be attributed
to racial genetic predisposition, different cultural back-
ground, and dietary habits . Consequently, there may
be the seasonality of flares or births of IBD patients in
China may show different patterns from those of IBD
patients in Western countries. The purpose of this study
was to determine whether symptom flares or births of
Chinese patients follow a seasonal pattern.
Patients and Methods
This study was performed in two gastroenterology (GI)
units: the Department of Gastroenterology, the First Affil-
iated Hospital, Nanchang University, and the Department
of Gastroenterology, the People’s Hospital of Yicheng.
Almost all of the UC patients came from the Westeast Lake
District and Nanchang County of Nanchang City, and
Yicheng County of Yicheng City. The diagnosis of UC had
been established by clinical, endoscopic, histological, and/
or radiological criteria . Endoscopy was performed in
most of the patients and revealed typical signs of UC.
Flares were diagnosed only on the basis of typical symp-
toms without endoscopy in a small proportion of the
patients. Infections or parasites were excluded by stool
culture and microscopic examination. Patients with a
diagnosis of UC colitis established between January 1990
and December 2007 were included in this study and
investigated for seasonality of flares of symptoms and the
month of births.
Data on the flares of symptom were retrospectively
assessed by the appearance of typical symptoms, such as
diarrhoea, abdominal pain, weight loss, perianal fistula/
abscess, rectal bleeding, extra-intestinal manifestations, or
of aggravated conditions of these symptoms so that
additional medical treatment—in additional to prior ther-
apy—was required. Only those patients who were able to
precisely indicate the exact month when symptoms
appeared or were aggravated were included in the statisti-
cal analysis. The expected flares or births during each year
were calculated according to the differences in the number
of days in the month of 1 year. Statistical analysis was
performed using the chi-square test, and statistical signifi-
cance was set at a P value of 0.05.
A total of 427 UC patients were investigated. The actual
months when disease flares or births occurred were estab-
lished in 409 of the 427 patients (95.7845%). Eighteen
patients were excluded because the month of disease flares
could not be established.
A total of 1030 flares of symptoms were determined
from the data collected from those 409 patients, and the
observed and expected frequency of disease flares per
month is shown in Table 1, taking into account the dif-
ference in the number of days in each month between
January 1990 and December 2007. Flare peaks occurred in
the spring and summer, especially in May, June, and
August, compared with the nadir in the winter (v2(11df)=
Table 2 shows the observed and expected frequency of
disease flares on a seasonal basis: spring (March, April,
May), summer (June, July, August), autumn (September,
October, November), and winter (December, January,
February). The ratio of observed to expected number of
Table 1 Observed and expected monthly frequency of disease flares
in 409 patients with ulcerative colitis (UC) between January 1990 and
Month of the yearObservedExpected
April 92 84.65753
September 91 84.65753
October 79 87.47945
Dig Dis Sci (2009) 54:1094–10981095
flares is 291:259.6, 296:259.6, 246:256.8, and 197:254.0
for the spring, summer, autumn and winter, respectively
(v2(3 df) = 32.74304, P\0.001).
Table 3 shows the observed and expected birth cases for
the 409 UC patients according to month, taking into con-
sideration the difference in the number of days in each
month, between January 1990 and December 2007. These
data are combined in Table 4 to show the seasonal distri-
bution of birth cases, and the data on birth distribution is
further condensed into a spring–summer and autumn–
winter pattern in Table 5. We found no statistical
difference in birth distribution in the different months
(P[0.1) or four seasons (P[0.1); however, more UC
patients were born in the autumn–winter period than in the
spring–summer period, with the ratio of observed to
expected number of births being 183:206.1808 for the
spring–summer period and 226:202.8192 for the autumn–
winter period (v2(1 df)= 5.255607, P\0.025).
The First Affiliated Hospital of Nanchang University is the
only main regional hospital for residents of the Westeast
Lake District and Nanchang County of Nanchang City,
central-eastern China, and the People’s Hospital of Yich-
eng has the same function for the residents of Yicheng
County, central China. Consequently, almost all UC
patients in these two areas are referred to these two hos-
pitals for medication, and the number of patients reported
here reflects the incidence of UC in these areas between
January 1990 and December 2007.
It is well known that environmental factors contribute to
inducement of IBD, but the relationship between season-
ality and flares of symptoms or births of IBD patients
requires further study as results to date have been incon-
sistent in terms of seasonal variations in the flares of
symptoms or birth cases of IBD patients. The results of
some studies suggest a degree of seasonality, with
increased rates of UC flares being found in the spring and
summer in an Italian population  or in spring and
autumn in Swedish populations , while another study
found monthly seasonality in symptomatic onset of UC in
December and January in a Norwegian population .
However, other studies have not found any seasonal pattern
of onset or relapse among patients with UC among British
 and American populations . Conflicting data have
also been reported for the seasonal variation of birth cases
in IBD patients. One study demonstrated that birth during
the winter period in Israel was associated with increased
risk to develop CD, whereas birth during the spring was
associated with a reduced risk , but another study did not
find any seasonality in month of birth of IBD in British
population of under 20-year-olds . These different
Table 2 Seasonal distribution of disease flares according to season
Table 3 Observed and expected number of birth cases among 409
UC patients according to months of the year patients
Month of the yearObserved Expected
Table 4 Seasonal distribution of birth cases among 409 UC patients
Table 5 Seasonal distribution of birth cases among 409 UC patients
based on a spring–summer and autumn–winter pattern
1096 Dig Dis Sci (2009) 54:1094–1098
results among study populations of different races in dif-
ferent geographic areas may reflect the distinct genetic
backgrounds of the study populations.
To date, little information on seasonal patterns in flares
of IBD or births of IBD patients has been collected among
Asian populations, especially the Chinese population. In
this study, we determined the seasonal patterns in disease
flares and births of patients with UC among a Chinese
population. We found a higher frequency of symptom
flares in the spring and summer, especially in May, June,
and August, with a much lower frequency during the
winter. In contrast, the distribution of births of UC patients
showed no statistical difference when analyzed on a
monthly basis, but most UC birth cases did occur during
the autumn–winter period than in the spring–summer per-
iod. These data are not consistent with those obtained from
Western populations, and the underlying factors for the
difference should be intensively studied.
The role of environmental factors in triggering IBD has
been the focus of attention for a long time, particularly with
respect to bacterial infections. Bacteria and bacterial anti-
gens can modulate the gut immune response and contribute
to intestinal inflammation [17, 18]. The tolerance which
exists under a normal healthy state towards resident
intestinal flora is broken in active IBD , which implies
the triggering role of bacterial infection in the flare of IBD.
As many human infectious pathogens appear in a regular
seasonal pattern [20, 21], seasonal exposure to infectious
agents may induce bursts of immune diseases, such as IBD
[22, 23], and there may be an association between the
month of birth and risk of developing IBD later in life .
In the Asian area, bacterial infections show a seasonal
pattern of occurrence that peaks in the spring and summer
[25, 26], but viral infections generally occur in the autumn
and spring , which is slightly different from the sea-
sonality found in Western populations according to a
number of epidemiological studies [28, 29]. The infection
pattern in the Asian area is consistent with the data of our
study, and this consistency may provide a clue for deter-
mining the link between bacterial infection and flares of
UC, and viral exposure in early life, such as during preg-
nancy or postpartum, with an increased chance of
developing UC later in life. The related studies and
potential mechanisms need to be further investigated.
Inflammatory bowel disease is triggered by an inap-
propriate immune activation in genetically predisposed
individuals . Exposure to seasonally variable external
factors during the maturation of the immune system is
suspected to be an inducing factor for IBD, with the
immune response varying in different seasons. For exam-
ple, the immune function decreases during the winter,
when there is a lower production of proinflammatory
cytokines and an increased TH1/TH2 ratio [30, 31], which
differs from those found during the summer and spring [32,
33]. The possible factors modulating the immune response
in different seasons and at different temperatures has been
studied by some groups. The warmer temperature can
facilitate the locomotion of human neutrophilic leukocytes
and lymphoblasts [34, 35] and thereby induce the release of
inflammatory mediators, such as interleukin (IL)-6 [36,
37]. These fluctuations in immune function in the different
seasons may explain the seasonal variations in symptom
flares of UC.
The production of adrenal corticosteroids, such as cor-
tisol, have an inhibitory effect on immune function . A
recent study which assayed the level of cortisol production
in normal individuals found seasonal rhythms in cortisol
concentration , with peak production occurring in the
spring and summer and the lowest production in the
autumn and winter. Seasonal fluctuations in cortisol con-
centration may play a negative role in immune diseases and
affect flares of UC.
In conclusion, the results of our analysis of UC patients
in a Chinese population are not consistent with those
obtained on Western populations and indicate that flares of
symptoms occurred mainly in the spring and summer,
especially in May, June, and August, and that the birth of
UC patients occurred more frequently in the autumn–
winter period than in the spring–summer period. The
environmental recurring factors may be associated with the
symptom flares of UC, and comparable factors during
pregnancy or postpartum may be associated with a sus-
ceptibility to UC later in life.
Creative Commons Attribution Noncommercial License which per-
mits any noncommercial use, distribution, and reproduction in any
medium, provided the original author(s) and source are credited.
This article is distributed under the terms of the
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