Can Vitamin B12 Deficiency be a Sign of Cancer

By Dr. Rahul Shekhar in Internal Medicine

Mar 20, 2025

Introduction

Vitamin B12 deficiency can be a sign of cancer, particularly in cases where it occurs alongside other persistent symptoms. While vitamin B12 deficiency causes fatigue, nerve disorders, and anaemia, research has shown concerning links between low B12 levels and several types of cancer, including stomach, pancreatic, and blood cancers.

This comprehensive guide examines the crucial connection between Vitamin B12 deficiency and cancer.

What Is Vitamin B12 & Why Is It Important?

Vitamin B12, also known as cobalamin, stands as a water-soluble nutrient that plays several crucial roles in maintaining bodily functions. Since the human body cannot produce this essential vitamin, obtaining it through diet or supplements becomes necessary.

At its core, vitamin B12 is a fundamental component for DNA synthesis & red blood cell formation. Moreover, this vitamin maintains the proper functioning of nerve cells and supports the myelination process in the central nervous system. The vitamin works alongside two key enzymes—methionine synthase and L-methylmalonyl-CoA mutase—to facilitate these vital processes.

The absorption of vitamin B12 follows a complex pathway. Initially, the vitamin binds with proteins in food and undergoes separation in the mouth through saliva. Subsequently, the freed vitamin combines with haptocorrin, a specific binding protein. The stomach's hydrochloric acid and gastric protease continue this process, ultimately leading to the vitamin binding with intrinsic factors for absorption in the distal ileum.

The recommended daily intake for adults aged 19 to 64 is approximately 1.5 micrograms. However, the Reference Daily Intake suggests a slightly higher amount of 2.4 micrograms, with increased requirements for pregnant or nursing individuals.

Primary dietary sources of vitamin B12 include:

Animal products such as meat, fish, and poultry
Dairy items, including milk, cheese, and yoghurt
Eggs and fortified breakfast cereals

Common Causes of Vitamin B12 Deficiency

Several medical conditions & lifestyle factors contribute to vitamin B12 deficiency. The most prevalent cause stems from absorption difficulties rather than dietary shortages.

Pernicious Anaemia: Pernicious anaemia is a significant factor behind B12 deficiency. It occurs when the body fails to produce an intrinsic factor, a crucial protein for B12 absorption. This condition appears more common in individuals with northern European or African ancestry.

GI Diseases: Digestive system disorders often interfere with B12 absorption. These include:

Celiac disease
Crohn's disease
Ulcerative colitis
Helicobacter pylori infection
Chronic pancreatic disease

Medications: Certain medicines can hinder B12 absorption over time. People taking heartburn medicines, especially proton pump inhibitors or metformin for diabetes, face an increased risk of developing B12 deficiency.

Age: Many older adults produce insufficient hydrochloric acid in their stomachs, making it harder to absorb naturally occurring B12 from food sources.

Surgery: Surgical procedures affecting the digestive system might compromise B12 absorption. Weight-loss surgery or gastrectomy often reduces B12 absorption capabilities. Similarly, surgeries that remove or bypass the end of the small intestine, where B12 absorption primarily occurs, can result in deficiency.

Lifestyle Choices: Excessive alcohol consumption impairs B12 absorption, with risk thresholds set at more than two drinks daily for men and more than one for women.

Dietary Habits: Dietary patterns play a role, though less commonly in developed nations. Strict vegetarians and vegans face increased risks due to the absence of natural B12 in plant-based foods. This risk extends to breastfed infants of vegan mothers.

Genetics: Genetic conditions, though rare, can cause severe B12 deficiency. These include Imerslund-Gräsbeck syndrome, inherited intrinsic factor deficiency, and transcobalamin II deficiency.

Symptoms and Signs of B12 Deficiency & When to Be Concerned

Physical symptoms often emerge gradually as B12 levels decline in the body. Fatigue is one of the earliest indicators, alongside unexplained weakness and shortness of breath. The body's inability to produce healthy red blood cells leads to pale or yellowish skin, reflecting the underlying anaemia.

Digestive disturbances frequently accompany B12 deficiency. People might notice decreased appetite, indigestion, or alternating bouts of diarrhoea and constipation. A notably sore or inflamed tongue, sometimes accompanied by mouth ulcers, signals potential B12 depletion.

Neurological manifestations deserve particular attention because they might become permanent without timely treatment. These symptoms include:

Numbness and tingling in hands and feet
Problems with balance and coordination
Muscle weakness- affecting movement
Vision disturbances
Memory difficulties and confusion

Mental health changes accompany B12 deficiency, ranging from mild depression to severe psychological issues. Individuals might experience:

Mood swings and irritability
Difficulty concentrating
Changes in behaviour patterns
Cognitive decline

Certain symptoms warrant immediate medical attention. Immediately contact a doctor if experiencing:

Persistent neurological symptoms
Severe fatigue affecting daily activities
Cognitive changes or memory problems
Vision disturbances
Unexplained mood changes

Can B12 Deficiency Indicate Cancer: Key Associations

Research reveals complex associations between vitamin B12 deficiency and various types of cancer. Studies indicate that certain cancers might affect B12 absorption, although a deficiency alone does not directly cause cancer.

Gastrointestinal cancers demonstrate significant connections with B12 deficiency. Stomach tumours can destroy cells that produce intrinsic factors essential for B12 absorption. In cases of pancreatic cancer, the disease affects enzymes involved in B12 digestion, leading to decreased absorption.

Blood cancers present unique challenges, as they affect bone marrow production of red blood cells, consequently impacting B12 levels. Patients with leukaemia or multiple myeloma often exhibit symptoms similar to B12 deficiency anaemia.

Recent studies highlight concerning correlations between B12 levels and specific cancer types:

Breast Cancer: Research found significantly lower B12 concentrations in menopausal and post-menopausal breast cancer patients
Cervical Cancer: Studies revealed a higher risk of HPV infection, responsible for 99.8% of cervical cancer cases, in individuals with insufficient B12 levels
Colorectal Cancer: Research demonstrated a reduction in cancer risk with every 4.5 µg increase in dietary B12 intake.

Medical Conditions That Mimic B12 Deficiency

These include:

Multiple sclerosis often mirrors B12 deficiency symptoms through neurological manifestations. Both conditions affect the nervous system, causing similar symptoms like fatigue, weakness, and cognitive changes. Accordingly, doctors must conduct thorough evaluations to differentiate between these conditions.
Myelodysplastic syndrome (MDS) presents another diagnostic challenge. Recent studies highlight cases where patients with normal B12 levels received initial MDS diagnoses based on bone marrow biopsies. Upon detecting elevated methylmalonic acid levels, doctors revised these diagnoses to B12 deficiency.
Several other medical conditions frequently mistaken for B12 deficiency include:

Chronic fatigue syndrome
Fibromyalgia
Dementia and Alzheimer's disease
Depression and bipolar disorder
Parkinson's disease
Functional neurological disorder

Age-related concerns often mask B12 deficiency symptoms. Doctors sometimes attribute symptoms like tiredness, memory loss, and cognitive dysfunction to natural ageing, even in patients as young as their early fifties.
Thiamine-responsive megaloblastic anaemia syndrome (TRMA) resembles B12 deficiency. This inherited condition causes megaloblastic anaemia between infancy and adolescence, alongside hearing loss and diabetes mellitus.

How to Diagnose & Treat B12 Deficiency

Blood tests serve as the primary method for diagnosing vitamin B12 deficiency. Doctors typically start with a complete blood count (CBC) to check haemoglobin levels and red blood cell size. A serum B12 level below 200 pg/mL indicates deficiency, whereas values between 200-300 pg/mL suggest borderline status.

In cases where initial results remain unclear, doctors order additional tests. These include measuring methylmalonic acid (MMA) and homocysteine levels in the blood. Both markers rise as B12 levels decline, offering more precise diagnostic insights.

Upon confirming B12 deficiency, treatment approaches vary based on underlying causes. For diet-related deficiencies, oral B12 supplements taken between meals often prove sufficient. Yet, individuals with absorption issues, namely those with pernicious anaemia, require different interventions.

The standard treatment protocol involves the following:

Intramuscular B12 injections (hydroxocobalamin)
Initial dosing every other day for two weeks
Maintenance doses every 2-3 months thereafter
Regular blood tests to monitor B12 levels

Conclusion

Understanding the relationship between vitamin B12 deficiency and cancer requires careful consideration of multiple factors. While B12 deficiency alone does not cause cancer, it serves as a potential warning sign for several types of cancer, especially gastrointestinal malignancies.

Doctors now recognise that B12 deficiency symptoms overlap with various conditions, making accurate diagnosis essential. Regular blood tests help identify true B12 deficiency cases, allowing healthcare providers to start appropriate treatment before permanent damage occurs.

The treatment path depends largely on the underlying cause. Some patients respond well to oral supplements, while others need regular B12 injections. People experiencing persistent symptoms of B12 deficiency should seek medical attention, particularly when traditional supplements fail to resolve the issue.

FAQs

Can Vitamin B12 Deficiency Be Reversed Without Medical Help?

Mild cases might improve through dietary changes alone.

Does Cancer Treatment Always Lead to B12 Deficiency?

Not necessarily. Yet, chemotherapy might damage the gastrointestinal lining, potentially causing absorption issues in certain patients.

Are Plant-Based Diets Linked to Higher Cancer Risk Due to B12 Deficiency?

Vegans and vegetarians face increased risks of B12 deficiency. However, the connection between these diets and cancer risk depends on various factors, including overall health status and genetic predisposition.

How Long Until B12 Treatment Shows Results?

Recovery timing varies and depends on the severity of the deficiency & its underlying causes. However, most individuals notice improvements within weeks of starting appropriate treatment.