- The appendix stores beneficial bacteria that can reseed the gut after illness.
- People who had appendectomies face a 73% higher colorectal cancer risk over 20 years.
- Appendectomy is also linked to higher rates of C. difficile, IBD, and possibly Parkinson's.
William Parker had spent years studying the slimy coating inside human intestines when he noticed something peculiar about the appendix. The finger-shaped organ, long dismissed as evolution's leftover junk, was wrapped in an unusually thick layer of protective bacteria.
In 2007, Parker's team at Duke University proposed what seemed like a radical idea: the appendix wasn't useless at all. It was a safe house.
The proposal met skepticism. Medical textbooks had treated the appendix as vestigial for over a century. Surgeons routinely removed it at the first sign of inflammation. Antarctic expeditions and some space programs required prophylactic appendectomies for participants heading to remote locations.
Why keep an organ that might cause deadly peritonitis when help is months away?
Key figure
73%
Increased colorectal cancer risk in people who had appendectomies, over 20 years of follow-up
The Bacterial Reservoir
Parker's intuition proved prescient. The appendix, it turns out, harbors a distinct community of microbes unlike anywhere else in the gut. Its narrow shape and protected position near the junction of the small and large intestines make it difficult for the contents of diarrhea to flush clean.
When disease strips the colon of its microbial inhabitants, the appendix can reseed the gut with beneficial bacteria.
What is the gut microbiome?
Trillions of bacteria, fungi, and other microorganisms live inside your digestive tract. This community helps break down food, produces vitamins, and trains your immune system to distinguish friend from foe. An imbalanced microbiome has been linked to conditions from inflammatory bowel disease to depression.
Recent research has painted an increasingly detailed picture of what happens when this reservoir disappears.
Ignacio López-Goñi, a microbiologist at the University of Navarra, writes in The Conversation that people who undergo appendectomies show reduced populations of bacteria that produce short-chain fatty acids. These compounds help maintain the gut lining and regulate inflammation throughout the body.
The Long-Term Evidence
A 2022 study published in Oncogene tracked over 129,000 adults in Hong Kong for two decades. Those who had undergone appendectomies faced a 73% higher risk of developing colorectal cancer compared to matched controls. The researchers found that appendectomy patients harbored elevated levels of seven cancer-promoting bacterial species and depleted populations of five beneficial ones.
The connection extends beyond cancer.
Appendectomy has been associated with increased risk of recurrent Clostridium difficile infections, inflammatory bowel disease, and possibly even Parkinson's disease.
The appendix's lymphoid tissue produces immunoglobulin A, an antibody crucial for controlling which microbes colonize the gut.
A Policy Reversal in Space
These findings have quietly reshaped medical protocols for some of Earth's most isolated environments.
The Australian Antarctic program required prophylactic appendectomies for winterers starting in 1950. Russia, the United Kingdom, and several other nations used similar policies intermittently for their polar expeditions.
NASA never mandated the procedure for American astronauts, though the possibility was debated for decades. Today the agency's position is unambiguous: the potential risks of removing the appendix outweigh the benefits, even for missions where emergency surgery would be impossible.
Most surgeries occur during emergencies when the organ has already failed.
For a journey to Mars lasting two to four years with evacuation times measured in months, NASA would rather maintain astronauts' gut health than eliminate a small risk of appendicitis.
For the roughly 300,000 Americans who undergo appendectomies each year, the emerging science raises questions without easy answers. Most surgeries occur during emergencies when the organ has already failed. But the research suggests we should think twice before removing healthy appendixes incidentally during other procedures.
What evolution preserved for millions of years might be worth keeping after all.
Sources
- Primary Research: Shi et al. (2022) "Altered gut microbiome composition by appendectomy contributes to colorectal cancer" Oncogene
- Additional Context:
- Why the appendix is much more important than we once thought (The Conversation)
- Prophylactic surgery prior to extended-duration space flight (Canadian Journal of Surgery)
- Appendix Isn't Useless At All (ScienceDaily / Duke University)
Fact Check: Claim-by-Claim Verification Verified
The recap accurately represents the cited source article and supporting peer-reviewed studies on the appendix's role, the 73% colorectal cancer risk increase from the Shi et al. study, and related health associations.
Commentary
- The Hong Kong study's sample size (~129,000 total) slightly mismatches some reports (~129k vs. 43k cases +85k controls), but key 73% figure and findings align precisely.
- Appendectomy-CRC link shows geographic variation (stronger in Asian/American cohorts, neutral in Europeans per meta-analyses); causation not definitively proven.
- López-Goñi article notes reduced SCFA-producing bacteria post-appendectomy, consistent with microbiome research.
Sources used for verification
Academic/Peer-reviewed:
- Altered gut microbiome composition by appendectomy contributes to colorectal tumorigenesis - PubMed
- Biofilms in the large bowel suggest an apparent function of the human vermiform appendix - PubMed
- Prophylactic surgery prior to extended-duration space flight - PMC
- Risk of colorectal cancer after appendectomy: A systematic review and meta-analysis - PubMed
Other reliable sources:
- Why the appendix is much more important than we once thought - TheConversation.com
- Appendix Isn't Useless At All - ScienceDaily.com
- Health requirements for Australian Antarctic stations - Antarctica.gov.au
Fact-checked by Perplexity Sonar Pro on 2026-01-15
