Vitamin B12 Deficiency and Cancer: What the Research Really Says
Vitamin B12 deficiency is not a direct sign of cancer, but scientific studies do show some interesting connections. In many cases, low B12 levels appear more often in people with certain cancers—especially early-stage gastrointestinal cancers. However, the evidence is still mixed because several studies also report no definite link.
What we do know is this: cancer can sometimes cause B12 deficiency, and long-term low B12 may slightly influence cancer risk in a few organs.
Can Vitamin b12 deficiency be a sign of cancer ?
Table of Contents
Why Vitamin B12 Deficiency Happens
Most people don’t become deficient because they aren’t eating enough B12. Instead, the problem usually lies in poor absorption. Some common reasons include:
- Pernicious anemia: the immune system damages stomach cells that help absorb B12
- Stomach or intestinal surgeries
- Long-term use of certain medicines, such as metformin or proton pump inhibitors (PPIs)
- Digestive disorders that affect nutrient absorption
In cancer patients, tumors in the gastrointestinal tract can physically block absorption or damage the stomach lining, which reduces intrinsic factor — the key protein needed to absorb B12.
Types of Cancer Often Linked With Low B12
- Stomach (Gastric) Cancer
People with pernicious anemia have a higher risk of stomach cancer. Tumors in the stomach can directly interfere with B12 absorption.
- Colorectal Cancer
Many studies notice lower B12 levels in the early stages of colorectal cancer. Researchers think this occurs because cancer alters the way the intestines absorb nutrients.
- Blood Cancers (Leukemia, Lymphoma)
These cancers disrupt bone marrow and red blood cell production, causing symptoms that look similar to B12-deficiency anemia.
- Pancreatic and Liver Cancer
These organs help process and activate B12. When they are affected by cancer, B12 metabolism becomes impaired.
In some blood cancers, B12 levels can even appear falsely high because cancer cells release more B12-binding proteins.
How Cancer Affects B12 Levels
Cancers in the stomach and intestines can destroy cells needed for B12 absorption or block pathways through which nutrients travel.
Vitamin B12 plays a key role in DNA methylation, a process that protects DNA from damage. Chronic deficiency can disrupt this process, potentially raising cancer risk in digestive organs.
Interestingly, a few studies also point out that excessively high B12 intake may increase colorectal cancer risk — highlighting that balance is crucial.
What Research Shows (and Why Results Differ)
- Some studies link low B12 with higher risks of stomach, breast, and colorectal cancers.
- A 2024 study of 788 cancer patients found B12 deficiency common in cancers like colorectal cancer.
- Animal research shows that diets very low in B12 can cause DNA mistakes that may lead to cancer.
- But other studies show no clear cause-and-effect relationship.
- There is also evidence that too much B12 might not be ideal, and very low intake (like strict vegan diets without supplements) could pose risks.
Overall: the connection exists, but it’s complex and not fully proven.
Symptoms: When Should You Be Concerned?
Symptoms of B12 deficiency often resemble early cancer symptoms, including:
- Tiredness and weakness
- Anemia
- Numbness or tingling
- Memory or concentration problems
- Pale skin
If your B12 stays low despite a good diet and no known medication issues, doctors may investigate further to rule out hidden gastrointestinal problems, including tumors.
Diagnosis and Treatment
Doctors usually check:
- Serum B12 levels
- Complete blood count (CBC)
- Methylmalonic acid (MMA) — the most accurate indicator of B12 deficiency
For treatment, high-dose oral supplements (1–2 mg/day) work as well as injections for most people. If cancer or another underlying issue is causing the deficiency, that must also be treated.
Vegetarians, vegans, and older adults may need regular supplements or fortified foods.
Prevention and Reducing Risks
- Eat foods rich in B12: meat, dairy, eggs, fish
- Use supplements if you’re vegetarian, vegan, or unable to absorb nutrients well
- Treat early digestive issues or anemia promptly
- Monitor B12 levels after stomach or intestinal surgery
If B12 remains low without a clear reason, it’s smart to see a doctor, as it might point to a hidden condition that needs attention.
