The role of the appendix in preventing depression

The remarkable link between this misunderstood appendage and the brain

A few years ago, researchers conducting a study into appendectomy and small bowel obstruction noticed a striking pattern. There was a ‘surprisingly high proportion of psychiatric illness’ among people who’d had their appendix removed in childhood.

Appendectomy is the usual treatment for appendicitis, a very painful and potentially fatal condition, if left untreated.

The appendix is a pouch of tissue attached to the colon on the lower right-hand side of the abdomen. Why would its removal lead to psychiatric illness later in life? There is, at first, no obvious connection.

This wasn’t the first time that appendectomy had been linked to seemingly unrelated conditions. Previous observations included higher risk of colorectal cancer, cardiovascular disease, Parkinson’s disease, inflammatory bowel disease, gallstones, sarcoidosis, and rheumatoid arthritis.

Nor was this the first time that an association with psychiatric disease had been observed. Increased risk of depression, anxiety disorders and bipolar after childhood appendectomy was described in another Swedish study published in 2020.

Fortunately, the researchers who’d noticed this pattern decided to explore the matter further. Early this year (2025), the results of their exploration were published.

Their study involved 752 participants who had had childhood appendectomy. Each was individually matched to five similar people who had not had an appendectomy. Health data was collected from all participants.

Sure enough, the researchers found that ‘The risk of psychiatric illness in general … and affective disorders was higher among those with appendectomy.’

Until the early 2000s, the appendix was,considered a redundant evolutionary leftover, flapping about pointlessly. The only function it appeared to have was to make your life hell, should it become blocked and inflamed.

That was because nobody had figured it out. We humans can be a bit arrogant at times.

We had it all wrong. The appendix serves as a shelter for gut microorganisms, including bacteria, viruses, protozoa, archaea. It is a safe retreat for occasions when there are disturbances to the gut microbiome. Teeming with life, it is a ‘living organ in a delicate relationship with its human host’.

It is also part of the immune system, a lymphoid tissue and the main site of IgA production. IgA are the antibodies that fight specific infection in the digestive tract, preventing invading organisms from getting a foothold.

Even its location is relevant, being positioned away from faecal matter passing through the colon.

Despite what is now known, the NHS website (not updated since circa 1950) still states ‘You do not need your appendix, so it's not harmful to remove it.’

Appendicitis is inflammation of the appendix. This can occur if it becomes blocked, usually by a stone-like hard stool or piece of undigested food. It is a medical emergency and the most common surgical emergency in childhood. The lifetime risk of developing the condition is approximately 8%. If the appendix ruptures, bacterial infection can spread to the abdomen (peritonitis), which is why treatment must be given as soon as possible.

Although most cases occur between the age of 5 and 45, once you get past 60 the risk increases again. Furthermore, cases of acute appendicitis in older people are rising - 15% of patients aged 50 and above who turn up in the emergency department with acute abdominal pain are found to have appendicitis.

So what’s the link with psychiatric disorders?