Can Vitamin B12 Deficiency Be a Sign of Cancer? The Full Story
Key points
- Stomach Cancer: Tumors in the stomach can damage or destroy the parietal cells. These cells produce "intrinsic factor," a crucial protein that binds to vitamin B12 so it can be absorbed later in the small intestine. Without intrinsic factor, B12 from food cannot be used by the body.
- Pancreatic Cancer: The pancreas releases enzymes essential for detaching vitamin B12 from proteins in food, a critical first step for its absorption. As Medanta Hospital explains, pancreatic cancer can impair the production of these enzymes, leading to deficiency.
- Colorectal & Small Intestine Cancers: Tumors or surgeries affecting the ileum (the final section of the small intestine) can disrupt the primary site where B12 is absorbed into the bloodstream.
Experiencing symptoms like fatigue or brain fog can be concerning, and a blood test revealing a vitamin B12 deficiency often raises more questions than answers. A common worry is whether this nutritional gap could be a sign of something more serious, like cancer.
The short answer is that vitamin B12 deficiency is not a direct sign of cancer. However, the relationship between the two is complex and multifaceted. In some cases, a deficiency can be a consequence of cancer or its treatment, while certain underlying conditions that cause low B12 levels can also elevate your cancer risk.
This article provides a comprehensive look at the evidence, differentiating correlation from causation and explaining how and when these two health concerns are connected.
The Complex Relationship: Sign, Consequence, or Risk Factor?
Most medical sources agree that finding you have a B12 deficiency, in isolation, does not mean you have cancer. Most cases are caused by diet, age-related changes, or specific autoimmune conditions. However, the connection can be understood in three main ways:
- A Consequence of Cancer: This is the most established link. Certain cancers, particularly those affecting the digestive system, can directly interfere with the body's ability to absorb or process vitamin B12.
- A Result of an Underlying Risk Factor: Conditions like pernicious anemia are a primary cause of severe B12 deficiency. This same condition is also a known risk factor for stomach cancer. Here, the deficiency and the cancer risk share a common cause.
- A Potential Contributor to Cancer Risk: Some research, cited by the National Institutes of Health, suggests that B12 deficient diets can influence the genome and potentially increase cancer risk over time, though this link is less direct.
How Cancer Can Cause Vitamin B12 Deficiency
The most direct connection is when cancer or its treatments physically impair the body's complex B12 absorption pathway.
Gastrointestinal Cancers
Gastrointestinal (GI) cancers show the most significant link to B12 deficiency.
- Stomach Cancer: Tumors in the stomach can damage or destroy the parietal cells. These cells produce "intrinsic factor," a crucial protein that binds to vitamin B12 so it can be absorbed later in the small intestine. Without intrinsic factor, B12 from food cannot be used by the body.
- Pancreatic Cancer: The pancreas releases enzymes essential for detaching vitamin B12 from proteins in food, a critical first step for its absorption. As Medanta Hospital explains, pancreatic cancer can impair the production of these enzymes, leading to deficiency.
- Colorectal & Small Intestine Cancers: Tumors or surgeries affecting the ileum (the final section of the small intestine) can disrupt the primary site where B12 is absorbed into the bloodstream.
Blood Cancers
Cancers like leukemia or multiple myeloma affect the bone marrow, the body's factory for blood cells. This can disrupt the production of healthy red blood cells, a process heavily dependent on vitamin B12, and lead to symptoms of anemia that overlap with B12 deficiency.
The Impact of Cancer Treatments
Beyond the disease itself, treatments can also lead to deficiency. Chemotherapy can damage the lining of the GI tract, causing temporary malabsorption, while cancer-related loss of appetite and weight loss can lead to inadequate dietary intake of B12.
Conditions Linking B12 Deficiency and Cancer Risk
Sometimes, B12 deficiency is a prominent symptom of a separate condition that carries its own cancer risk.
Pernicious Anemia: The Strongest Link
Pernicious anemia is the most cited example. It is an autoimmune disorder where the body's immune system mistakenly attacks the parietal cells in the stomach. This destroys the body's ability to produce intrinsic factor and absorb B12. According to the American Cancer Society, people with pernicious anemia have an increased risk of developing stomach cancer.
The B12 Paradox: Are High Levels a Greater Concern?
Interestingly, some research points to a paradoxical connection: elevated vitamin B12 levels may be a stronger, though still not definitive, marker for hidden cancer than low levels.
A large-scale Danish study found that patients with high B12 levels (not caused by supplements) had an increased risk of being diagnosed with cancer soon after, especially liver cancer and certain blood cancers. The leading theory is that some tumors may secrete B12-binding proteins or that liver damage from cancer can cause the organ to release its large stores of B12 into the bloodstream. This highlights that any unexplained, abnormal B12 level—whether high or low—warrants a thorough medical evaluation.
Understanding Vitamin B12 Deficiency
To understand its connection to other health issues, it's helpful to know the basics of vitamin B12 deficiency itself.
What Is Vitamin B12 and Why Is It Important?
Vitamin B12, or cobalamin, is an essential water-soluble vitamin. Your body needs it for:
- Red blood cell formation
- DNA synthesis
- Proper neurological function and nerve cell health
Since our bodies cannot produce B12, we must get it from food—primarily animal products like meat, fish, eggs, and dairy—or supplements.
Common Symptoms of B12 Deficiency
The onset of symptoms can be slow and gradual. Being aware of the signs is crucial for early detection.
Image Source: Medanta
- Profound Fatigue and Weakness: A deep exhaustion that isn't relieved by rest is a hallmark sign, often related to anemia.
- Neurological Symptoms: This is a key differentiator from other deficiencies. Signs include:
- Numbness, tingling, or "pins and needles" in the hands and feet.
- Difficulty with balance and coordination.
- Confusion, memory problems, or "brain fog."
- Physical Signs:
- Pale or slightly yellow skin (jaundice).
- A sore, red, and smooth tongue (glossitis).
- Mouth ulcers or recurrent canker sores.
- Psychological Changes: Mood swings, irritability, depression, or changes in behavior.
The Four Stages of Deficiency
Vitamin B12 deficiency typically progresses through four distinct stages:
- Stage 1: Serum Depletion: B12 levels in the blood begin to drop, but the body's stores are still sufficient. There are usually no symptoms.
- Stage 2: Cellular Depletion: The body's stores of B12 are low, leading to biochemical changes. Blood tests may show elevated levels of homocysteine and methylmalonic acid (MMA), more sensitive markers of deficiency.
- Stage 3: Early Clinical Deficiency: Damage begins to occur, and early symptoms, particularly neurological ones like tingling, may appear.
- Stage 4: Severe Deficiency: Macrocytic anemia (abnormally large red blood cells) develops, and neurological symptoms become more severe. Without treatment, some neurological damage can become irreversible.
When to See a Doctor
If you are experiencing persistent symptoms of vitamin B12 deficiency, it is essential to consult a healthcare professional. Do not attempt to self-diagnose cancer based on a vitamin deficiency.
A doctor can perform simple blood tests to confirm a deficiency and investigate its underlying cause. As Baptist Health notes, you should be especially vigilant if your symptoms are accompanied by "red flag" signs such as:
- Unexpected and unexplained weight loss
- Persistent abdominal pain
- Rectal bleeding
- Jaundice (yellowing of the skin and eyes)
Determining the root cause—whether it's diet, an absorption issue like pernicious anemia, or another underlying condition—is the key to effective treatment and managing your overall health.
References
- American Cancer Society. (n.d.). Stomach Cancer Risk Factors. https://www.cancer.org/cancer/types/stomach-cancer/causes-risks-prevention/risk-factors.html
- Arendt, J. F. H., & Nexo, E. (2012). Cobalamin Related Parameters and Cancer Risk. In Vitamin B12. InTech.
- Loedin, A. K., et al. (2021). Is There a Carcinogenic Risk Attached to Vitamin B12? PMC, National Institutes of Health. https://pmc.ncbi.nlm.nih.gov/articles/PMC8126961/
- Medical News Today. (2025). Vitamin B12 deficiency and cancer: Are they connected?. https://www.medicalnewstoday.com/articles/can-vitamin-b12-deficiency-be-a-sign-of-cancer
- Medanta. (2025). Can Vitamin B12 Deficiency Be a Sign of Cancer?. https://www.medanta.org/patient-education-blog/can-vitamin-b12-deficiency-be-a-sign-of-cancer
- Baptist Health. (2025). Can Vitamin B12 Deficiency Be a Sign of Cancer?. https://www.baptisthealth.com/blog/cancer-care/can-vitamin-b12-deficiency-be-a-sign-of-cancer
About the author
Fatima Al-Jamil, MD, MPH, is board-certified in gastroenterology and hepatology. She is an Assistant Professor of Medicine at a university in Michigan, with a clinical focus on inflammatory bowel disease (IBD) and motility disorders.