Cohort studyindependent cross-checkabstract checked★ key study I-ORG-124 in-depth review

Tonsil removal and bowel inflammation: the family test

Increased Risk of Inflammatory Bowel Disease in Families with Tonsillectomy: A Danish National Cohort Study.

Overview

Bager P et al.. Epidemiology 2019 · PMID 30461527 · DOI 10.1097/EDE.0000000000000946

Even relatives of people who had their tonsils out had more Crohn's disease, suggesting shared family factors rather than the surgery itself.

Does the study support the specific claim? No · Methodological quality: high

Study explained simply

What did the researchers want to find out?: Test whether the tonsillectomy-IBD link is causal
How was the study done?: National cohort with family linkage
How many people, animals or samples were studied?: 7 million Danes
What was actually found?: Higher IBD risk after own and after relatives' tonsillectomy
How large was the observed effect?: Crohn RR 1.52 (own) and 1.22 (relative)
What do the results mean in everyday life?: The link is probably partly due to family factors
What are the study's limitations?: IBD only
What does it say about Elawady's specific claim?: Contradicts a causal reading of the claim
Do the results apply to Germany and Europe?: Directly applicable
What can explicitly not be concluded from this study?: Cannot exclude a small direct effect

Authors: Bager P et al.
Journal: Epidemiology
Year: 2019
Identifier: PMID 30461527 DOI 10.1097/EDE.0000000000000946
Verification: verified – PubMed efetch 2026-10-26; Crossref works API 2026-10-26
Retracted: no
Corrections: none
Extent checked: abstract only
Conflicts of interest and funding: Non-commercial support (PubMed).

Is the tonsillectomy-IBD association explained by hereditary/shared factors? Risk after own tonsillectomy versus after relatives' tonsillectomy.

Study design: Cohort study – Nationwide Danish cohort with kinship linkage (Poisson regression)
Population: Danish population
Country: Denmark
Period: 1977-2014
Sample size: 7,045,288 individuals; 276,673 tonsillectomised
Inclusion and exclusion criteria: National registers

Exposure / intervention: Own tonsillectomy; tonsillectomy in first-, second-, third-degree relatives
Comparator: No tonsillectomy / no tonsillectomised relatives
Endpoints: Crohn's disease, ulcerative colitis
Statistical methods: Rate ratios (Poisson)

Results: Own tonsillectomy: Crohn's RR 1.52 (1.43-1.61), UC RR 1.24 (1.18-1.29), elevated up to 20 years. Relatives' tonsillectomy: Crohn's RR 1.22 (1.17-1.27) first-degree, 1.14 (1.08-1.19) second-degree, 1.08 (1.01-1.15) third-degree; UC 1.10, 1.05, 1.03.
Absolute risks: Not reported
Authors' conclusion: Individuals with tonsillectomised family members were also at increased IBD risk, which calls into question a direct effect of tonsillectomy and points to shared hereditary or environmental factors.

Orienting tool: ROBINS-E
Type of assessment: simplified assessment (abstract only)
Full formal assessment: no
Overall risk of bias: low
Rationale: Negative-control style design (relatives) directly probes confounding.

A graded association with relatives' surgery (who were not operated themselves) is evidence of confounding by familial factors.

Best available test of whether tonsillectomy-autoimmunity associations are causal.

Chang 2026 and Ji 2016 show the association itself.

Danish; directly applicable.

Strong argument that at least part of the tonsillectomy-immune disease association is due to shared family factors rather than the operation.

Multidimensional assessment
Multidimensional assessment
Authenticity of the source	verified
Methodological quality	high
Risk of bias	low
Precision of results	high
Directness	indirect
Reproducibility	unknown
Consistency with the overall evidence	consistent
Regional transferability	high
Adequacy of the interpretation (by the archive)	not applicable

Similar family designs for other autoimmune diseases.