Swedish researchers have found in a sibling comparison study that acute appendicitis had a protective effect against ulcerative colitis. The study has been published in BMJ Open Gastroenterology.
Past literature has shown an inverse relationship between appendicitis and ulcerative colitis (UC). But recent research has suggested that this relationship is influenced by genetic or environmental factors. Hence researchers from Sweden conducted a cohort study to assess the inverse relationship between acute appendicitis and ulcerative colitis (UC) using a sibling comparison design to adjust for unmeasured familial genetic and environmental factors between 1984 and 2018.

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Using several Swedish national registers nearly 3.1 million Sweden residents were involved in the study. Fitting Cox hazards models, the risk for developing UC in individuals with and without acute appendicitis was calculated by the age of 20 years, adjusting for several potential confounding factors. Further, sibling-stratified analyses were performed to adjust for shared unmeasured familial confounding factors.
Results:
During 57.7 million person-years of follow-up, 20,848 out of 31, 25, 232 developed UC among those without appendicitis (3.63 (3.59–3.68) per 10 000 person-years), whereas only 59 out of 35,848 people developed UC among those with appendicitis before age 20 years (1.66 (1.28–2.14) per 10 000 person-years).
A reduced risk of UC development was found in those with acute appendicitis by age 20, compared with individuals who did not have appendicitis by this age.
A slight attenuation in this association was found when adjusting for shared familial confounders.
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By late adolescence, individuals with acute appendicitis had a lower risk of developing UC than those without. Shared familial environmental factors and genetics appeared to play a minor role in this association.
Further reading: Garcia-Argibay M, Hiyoshi A, Montgomery S. Acute appendicitis and ulcerative colitis: a population-based sibling comparison study. BMJ Open Gastroenterol. 2022;9(1):e001041. doi:10.1136/bmjgast-2022-001041