Does Low Iron Cause Pernicious Anemia? The Surprising Connection

December 30, 2025 •

3 min read

While many forms of anemia result from a lack of iron, pernicious anemia stems from a completely different issue: a vitamin B12 deficiency caused by an autoimmune condition. This does not mean low iron cause pernicious anemia, but rather, the two can co-exist due to underlying factors affecting absorption.

Quick Summary

Pernicious anemia is an autoimmune disorder leading to vitamin B12 malabsorption, not an iron deficiency. Low iron is a frequent coexisting condition, complicating diagnosis.

Key Points

Not a Direct Cause: Low iron does not directly cause pernicious anemia; pernicious anemia is an autoimmune condition causing vitamin B12 deficiency.
Shared Vulnerability: The autoimmune attack in pernicious anemia destroys stomach cells, leading to low stomach acid (achlorhydria), which impairs both B12 and iron absorption.
Coexistence is Common: A significant number of people with pernicious anemia also have an iron deficiency due to malabsorption caused by the same underlying condition.
Diagnostic Challenge: The opposing effects of B12 and iron deficiencies on red blood cell size (macrocytic vs. microcytic) can mask each other on blood tests, making diagnosis difficult.
Distinct Symptoms: While fatigue is a shared symptom, pernicious anemia uniquely causes neurological problems like numbness and memory loss, while iron deficiency can cause brittle nails or a sore tongue.
Treatment Differences: Pernicious anemia requires lifelong B12 supplementation (often injections), whereas iron deficiency is treated with iron supplements and addressing the root cause.

Pernicious Anemia vs. Iron Deficiency: A Tale of Two Anemias

Pernicious anemia and iron deficiency anemia are distinct types of anemia with different causes. Pernicious anemia is an autoimmune disease where the body cannot absorb vitamin B12, which is vital for making red blood cells. Iron deficiency anemia is caused by insufficient iron, needed for hemoglobin production. While low iron doesn't cause pernicious anemia, the conditions can coexist, often due to shared issues in the digestive system.

The Autoimmune Root of Pernicious Anemia

Pernicious anemia results from an autoimmune attack on parietal cells in the stomach. These cells produce intrinsic factor, necessary for B12 absorption, and hydrochloric acid, which helps release B12 from food and is needed for iron absorption. Damage to these cells leads to both B12 malabsorption and reduced iron absorption, explaining why iron deficiency is common in those with pernicious anemia.

Why Coexistence Complicates Diagnosis

Diagnosing anemia can be tricky when both pernicious anemia and iron deficiency are present. Pernicious anemia typically causes red blood cells to be larger than normal (high MCV), while iron deficiency makes them smaller (low MCV). When both occur, these opposing effects can normalize the MCV, potentially hiding both deficiencies. Doctors need to consider various lab results and symptoms for an accurate diagnosis.

Comparison of Pernicious Anemia and Iron Deficiency Anemia


Feature	Pernicious Anemia	Iron Deficiency Anemia
Underlying Cause	Autoimmune disease attacking stomach cells (parietal cells).	Insufficient iron for hemoglobin production due to diet, blood loss, or malabsorption.
Primary Deficiency	Vitamin B12 (Cobalamin).	Iron.
Red Blood Cell Size	Macrocytic (abnormally large).	Microcytic (abnormally small).
Key Symptoms	Fatigue, neurological issues (numbness, tingling), memory problems.	Fatigue, shortness of breath, pale skin, brittle nails.
Neurological Symptoms	Yes, common due to B12's role in nerve health.	No, not a typical symptom.
Treatment	Vitamin B12 supplements, often injections for life.	Iron supplementation (tablets or IV) and addressing the underlying cause.

The Importance of Correct Diagnosis and Treatment

Accurate diagnosis is crucial as treatments differ significantly. Treating only one deficiency while another exists can be ineffective or harmful. For example, giving folate alone for megaloblastic anemia can mask B12 deficiency and allow nerve damage to worsen. A comprehensive approach addressing all deficiencies is key to recovery.

Medical Evaluation and Management

Doctors diagnosing pernicious anemia will conduct tests for confirmation and to check for coexisting conditions like iron deficiency.

Blood Tests: These include a CBC to check red blood cell size (MCV), as well as B12 and folate levels. Elevated MMA and homocysteine levels can further indicate B12 deficiency.
Antibody Testing: Tests for antibodies against intrinsic factor or parietal cells can confirm the autoimmune cause of pernicious anemia.
Iron Panel: If iron deficiency is suspected, this panel measures serum iron, ferritin, and TIBC.
Addressing the Cause: The doctor will also identify and treat the reason for iron deficiency, such as heavy menstrual bleeding or gastrointestinal issues.

Conclusion

In conclusion, low iron does not cause pernicious anemia, which is an autoimmune condition causing B12 malabsorption. However, the same autoimmune process can impair iron absorption, leading to frequent coexistence of the two conditions. Proper diagnosis involves a thorough review of symptoms and lab tests to identify all nutritional deficiencies. Treating both B12 and iron deficiencies appropriately is vital for managing these conditions and preventing complications. For more information on the coexistence of these conditions, consult this study from the National Institutes of Health.

Frequently Asked Questions

Yes, pernicious anemia can lead to low iron. The autoimmune gastritis that causes pernicious anemia also reduces stomach acid, which impairs the body's ability to absorb dietary iron.

Pernicious anemia is primarily caused by an autoimmune reaction where the body's immune system attacks and destroys the parietal cells in the stomach that produce intrinsic factor, a protein needed for vitamin B12 absorption.

Both can cause fatigue, but pernicious anemia is specifically associated with neurological issues like numbness, tingling, and memory problems. Iron deficiency is associated with symptoms like pale skin, brittle nails, and a sore tongue.

Yes, it is very common to have both conditions simultaneously. The underlying cause of pernicious anemia—autoimmune gastritis—creates an environment that impairs the absorption of both vitamin B12 and iron.

Doctors use a combination of tests. A complete blood count (CBC) looks at red blood cell size (MCV). Further tests measure serum B12, folate, ferritin, and intrinsic factor antibodies to identify the specific deficiency.

No, treating low iron does not fix pernicious anemia. Pernicious anemia requires B12 supplementation, usually via injection. Treating only the iron deficiency would not address the root cause of the B12 malabsorption.

Diagnosing coexisting conditions is challenging because the opposing effects of B12 deficiency (large red blood cells) and iron deficiency (small red blood cells) can cancel each other out, leading to misleadingly normal lab results for red blood cell size (MCV).