Introduction

When people hear the word “anaemia,” they often think of iron deficiency. But there is another, less-known form called pernicious anaemia, an autoimmune condition that prevents the body from absorbing vitamin B12, a nutrient essential for healthy red blood cells and maintaining proper nerve function.

What makes pernicious anaemia especially unique is that it begins in the digestive system, particularly in the stomach and small intestine. In this article, we’ll explore how this condition develops, how it affects your gut, and what to look out for.

What is pernicious anaemia?

Pernicious anaemia is a rare autoimmune disease characterised by a vitamin B12 (cobalamin) deficiency caused by impaired absorption rather than a dietary lack of vitamin B12. This occurs when the immune system mistakenly attacks parietal cells in the stomach lining. These cells are responsible for producing intrinsic factor, a protein that binds to vitamin B12 and allows it to be absorbed in the ileum, the final part of the small intestine.¹

Without the intrinsic factor, vitamin B12 cannot be properly absorbed, leading to the production of abnormally large and immature red blood cells (a condition known as megaloblastic anaemia). As a result, patients experience symptoms seen in anaemia, such as fatigue, weakness, and in some cases, neurological symptoms such as numbness and memory issues.¹

How is the digestive system affected? 

Pernicious anaemia isn’t just a blood issue. It actually starts in the digestive system, specifically in the stomach and small intestine. 

The role of the stomach 

Pernicious anaemia begins with the destruction of parietal cells in the stomach, which results in decreased production of both stomach acid and intrinsic factor. Stomach acid is essential for releasing vitamin B12 from food, and intrinsic factor is crucial for its absorption. This damage leads to a condition called autoimmune gastritis, or inflammation and thinning of the stomach lining over time.^2,5

The role of the intestine

The absorption of B12 occurs in the ileum, or the last part of the small intestine. 

Even if an individual with pernicious anaemia consumes B12-rich foods and B12 supplements, without the intrinsic factor present, B12 would not be absorbed into the bloodstream and transported to different parts of the body. This is where the key issue with this condition lies. Eventually, this malabsorption of B12 can lead to different symptoms such as digestive discomfort like bloating, flatulence, or diarrhoea. 

It can lead to a buildup of undigested nutrients and bacteria in the gut, which may trigger gut microbiome imbalance or further inflammation. Research suggests that patients with this condition have a higher risk of developing gastric cancer, and the presence of antibodies against intrinsic factor correlates with a higher incidence of malignancies.³ 

Diagnosis 

The first line of diagnosis involves understanding the clinical symptoms that the patient experiences. These could include:¹

• Fatigue and weakness
• Yellowing of the skin
• Shortness of breath
• Rapid heartbeat and or palpitations
• Dizziness

These could occur because of a reduction in the number of healthy red blood cells. The B12 deficiency could lead to neurological symptoms such as:⁴ 

• Numbness or tingling in the hands and feet
• Issues with balance or difficulty walking 
• Memory loss or confusion 
• Mood changes like irritability or depression
• Cognitive decline or even dementia-like symptoms (in severe cases)

As pernicious anaemia begins in the digestive system, patients may experience: 

• Loss of appetite, bloating, gas, or abdominal discomfort 
• Diarrhoea or constipation 
• A red, swollen, and smooth appearance of the tongue due to loss of papillae (the small bumps on the tongue that help with taste, texture, and sensation) 
• Pain or tenderness may occur, leading to difficulty in chewing, swallowing, or speaking

Other problems may be: 

• A blurred or double vision due to optic nerve involvement
• Weight loss related to poor appetite or malabsorption
• Increased susceptibility to infections

However, the clinical symptoms are not sufficient to confirm the diagnosis since they are often insidious for various reasons. The beginning and progression of the pernicious anaemia are very slow. As a consequence, patients often are not aware of their symptoms related to anaemia, because over time they have become used to them. 

In many such cases, the underlying disease may not be suspected until a complete red blood count has been performed to check your red blood cells. In pernicious anaemia, red blood cells are often larger than normal, a condition known as macrocytosis. It may also show low haemoglobin and low haematocrit, confirming anaemia.² Combining this test with the vitamin B12 blood level, where a low level supports the diagnosis of B12 deficiency. Yet, this test alone isn't enough, since other conditions can cause low B12.⁶

For confirmation, an antibody test is performed, looking for antibodies that attack intrinsic factor and against the cells in the stomach lining. If these results are positive, it strongly suggests a diagnosis of pernicious anaemia. 

Other biological markers may be demanded to confirm the origin of the condition. These could include:

1. Gastrin: a hormone produced by cells in the stomach lining that stimulates the stomach to produce gastric acid 
2. Pepsinogen: an inactive enzyme precursor secreted by chief cells in the stomach. When converted into pepsin, the active form, it helps break down proteins in the stomach

In the case of pernicious anaemia, increased levels of fasting gastrin and decreased levels of pepsinogen are well-accepted serological markers. This should be confirmed, however, by appropriate testing of the gastric body mucosa by an endoscopy.⁷

Treatment 

Pernicious anemia is a lifelong condition, but it is treatable.

As B12 is not absorbed by the body through the stomach due to the decrease in levels of intrinsic factor available, it must be administered via an injection. This allows for the levels of B12 to be replenished quickly and for some relief from the symptoms. The frequency of B12 injections varies as time progresses.⁸

Consuming haematinic-rich food (which contains iron, B12, and folate) can help with overall health. Avoiding alcohol and quitting smoking can help with managing symptoms, as these may worsen the stomach lining further. Keeping up a close observation of the patient, monitoring the symptoms, and following up on the treatment plan are important. 

Conclusion

Pernicious anaemia is far more than a blood disorder. At its core, it is a condition that originates within the digestive system, specifically affecting the stomach and small intestine. The disease begins when the immune system attacks the parietal cells in the stomach lining, impairing the production of intrinsic factor and stomach acid. These elements are essential for the proper digestion of food and the absorption of vitamin B12.

As a result, even when the diet is rich in vitamin B12, the body cannot absorb it efficiently due to the loss of intrinsic factor. This impaired absorption primarily occurs in the ileum, the final part of the small intestine, where vitamin B12 is normally taken into the bloodstream. The consequences are not limited to blood and nerve health. The digestive tract itself suffers from inflammation, nutrient malabsorption, discomfort, and in some cases, long-term complications such as gastric atrophy or malignancies.

Understanding the role of the stomach and small intestine in the development of pernicious anaemia is crucial for effective diagnosis and treatment. Early recognition and appropriate management with lifelong vitamin B12 supplementation can prevent irreversible complications and support both digestive and systemic health. It is essential to consider gastrointestinal health not just as a symptom of the disease, but as its foundation.

Summary

Your gut and your blood are more connected than you think, and taking care of one means protecting the other. Pernicious anaemia is an example of this. It might sound like a rare medical term, but it’s a condition that quietly starts in your stomach and can affect your entire body. It happens when your immune system damages the cells in your stomach that help absorb vitamin B12, a vitamin your body needs to make healthy blood and keep your brain and nerves working properly.

Even if you're eating well, your body can’t use B12 without a special protein called intrinsic factor, which your stomach stops making in this condition. Over time, this can lead to tiredness, memory issues, and even problems with the digestive system. Over time, this leads to chronic inflammation of the stomach lining (autoimmune gastritis), reduced stomach acid, difficulty in digestion, and malabsorption in the intestines, leading to bloating, gas, diarrhea, or nutrient deficiencies.

The good news? Once it’s diagnosed, pernicious anemia is treatable. Most people just need regular B12 injections or high-dose supplements, along with some follow-up care. Catching it early makes a big difference. If you notice any related symptoms, it could be your gut telling you something more serious. Don’t ignore it.