Background and aims: Reports on seasonality 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 January 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 consideration 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 winter, especially in January (chi(2) ((11 df))=32.74304, P<0.005). The symptom flares also occurred more frequently in the spring-summer period than in the autumn-winter period (chi(2) ((3 df))=22.1269, P<0.001). There was no statistical difference in birth distribution on a monthly or seasonal (spring, summer, autumn, winter) basis. However, the births of UC patients occurred more frequently in the autumn-winter period than in the spring-summer period when the data were merged into these two seasonal components (chi(2) ((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 susceptibility to UC later in life.