High vitamin B12 levels and cancer: how they’re related

Vitamin B12, also known as cobalamin, is part of the vitamin B complex — a group of eight vitamins that support everything from optimal cognitive function to converting the carbohydrates you consume into usable energy.¹

Stored primarily in the liver, vitamin B12 plays an important role in several essential bodily functions, including:²

• DNA synthesis
• Healthy red blood cell formation
• Central nervous system development and function
• Enzyme function

Interest in vitamin B12’s role in long-term health has grown in recent years — not only because it helps support neuron function, learning, and memory, but also because some research has explored whether elevated vitamin B12 levels may be associated with certain cancers.³

Research on the relationship between vitamin B12 and cancer is still in its early stages, and science-backed findings remain inconclusive. That said, there are several hypotheses to be aware of if you're concerned about the link between high vitamin B12 levels and cancer.

Excessive Vitamin B12 May Increase the Risk of Lung and Colon Cancer

A large-scale 2017 study published in the Journal of Clinical Oncology found that males who supplemented with “megadoses” of vitamins B6 and B12 had a 30% to 40% increased risk of lung cancer compared to individuals who did not supplement.⁴

However, the elevated risk was observed specifically among male current smokers. Additionally, participants consumed approximately 23 times the recommended daily intake over a period of 10 years. Female participants in the study did not demonstrate an increased risk of lung cancer.

Based on these findings, the study authors concluded that vitamin B12 supplementation should not be considered a “chemopreventive” strategy for lung cancer and may potentially have the opposite effect.⁴

In a follow-up study, researchers found that supplementing with vitamins B12 and B9 (folic acid) may increase the risk of colon cancer. These nutrients are often used to support bone health and reduce osteoporosis risk. However, researchers emphasized that larger and more comprehensive studies are still needed before definitive conclusions can be made.

High Vitamin B12 Levels May Be a Biomarker of Cancer

A 2013 study published in the Journal of the National Cancer Institute reported that elevated serum cobalamin (vitamin B12) levels were associated with:⁵

• Subsequent cancer diagnoses, particularly within the first year of follow-up
• An increased risk of smoking-related, hematological (blood-related), and alcohol-related cancers

Researchers concluded that elevated vitamin B12 levels may serve as a potential biomarker for cancer. This hypothesis was further supported by a separate 2020 study, which found that unexplained high serum vitamin B12 levels may be associated with the development of solid cancers, such as breast cancer.⁶ However, additional research is still needed.

Importantly, it remains unclear whether the disease process itself may contribute to elevated vitamin B12 levels.⁷ Researchers from the 2020 study also noted that the increase in vitamin B12 was likely unrelated to typical dietary intake or standard supplementation because food and supplements generally do not substantially affect plasma B12 concentrations.

Vitamin B12 May Not Have an Effect at All

On the other hand, an earlier study published in the American Journal of Epidemiology found no association between vitamin B12 levels and an increased risk of lung cancer.⁸

So, where does this leave us?

While current evidence surrounding vitamin B12 and cancer risk remains mixed, these findings underscore the importance of evaluating your nutrient levels before starting a vitamin B12 supplement. Always consult with your healthcare provider before adding any new vitamin or mineral supplement to your routine.

As these findings demonstrate, the increased risk of lung cancer observed in some studies was associated with extremely high doses of vitamin B12 — approximately 23 times the recommended daily intake of 2.4 micrograms.⁹

Other research has suggested that elevated vitamin B12 levels may occur as part of the disease process itself. Unlike fat-soluble vitamins, vitamin B12 is water-soluble, meaning excess amounts are typically excreted through urine.

In the absence of vitamin B12 supplementation, unusually high vitamin B12 levels in the bloodstream may sometimes indicate underlying health conditions, including:¹⁰

• Several forms of liver disease, such as acute hepatitis, cirrhosis, and liver cancer
• Certain blood cancers, including leukemia and polycythemia vera
• Hypereosinophilic syndrome, a group of blood disorders that may lead to organ damage¹¹

Not necessarily, but it’s recommended that you consult with your healthcare provider if you suspect you have elevated vitamin B12 levels. This is especially important if you experience symptoms commonly associated with high vitamin B12 levels in the blood, including:⁹

• Gastrointestinal issues, such as nausea, vomiting, or diarrhea
• Headaches
• Tingling sensations in the hands and feet
• Weakness and fatigue

Experts generally agree that consuming appropriate amounts of vitamin B12 is safe.⁹ Even amounts that exceed the recommended daily intake of 2.4 micrograms are not typically considered toxic because excess vitamin B12 is usually excreted through urine.⁹

In some cases, symptoms associated with elevated vitamin B12 levels may actually occur in people undergoing treatment for a vitamin B12 deficiency rather than from excessive intake itself.⁹

Ultimately, assessing your vitamin B12 levels through serum testing may provide peace of mind if you’re concerned about elevated levels. If testing reveals unusually high vitamin B12 concentrations, you and your healthcare provider can work together to identify potential underlying causes and determine an appropriate next step or treatment plan.

Most people obtain the majority of the vitamin B12 they need each day through foods such as:^2,9

• Fortified cereals
• Dairy products like yogurt, cottage cheese, and cheese
• Meat, poultry, and fish
• Nutritional yeast

However, some individuals may need to prioritize additional vitamin B12-rich foods or supplementation, including those who:

Are Vegan or Vegetarian

With the exception of fortified foods, vitamin B12 is naturally found almost exclusively in animal-based food sources.⁹ As a result, vegans and vegetarians may benefit from vitamin B12 supplements or fortified foods to help maintain healthy levels.² Additionally, infants who are breastfed by vegan mothers may be at greater risk of developing low vitamin B12 levels.²

Are Older Adults

Vitamin B12 deficiency becomes more common with age. Some estimates suggest that up to 43% of adults may have low vitamin B12 levels, particularly individuals with atrophic gastritis, a condition that commonly affects adults over age 65.²

Have Pernicious Anemia

Pernicious anemia is an autoimmune condition caused by the body’s inability to properly absorb vitamin B12.¹² Most commonly diagnosed in adults between ages 60 and 80, pernicious anemia can interfere with red blood cell production and may lead to permanent nerve damage if left untreated.

Have a Gastrointestinal Disorder

Individuals with gastrointestinal conditions such as Crohn’s disease or celiac disease may have difficulty absorbing adequate amounts of vitamin B12.² Similarly, people who have undergone gastrointestinal procedures, including weight loss surgery, may be at increased risk of vitamin B12 deficiency.² In many cases, healthcare providers may recommend vitamin B12 supplementation or cobalamin injections to help restore healthy levels.

When your nutritional needs aren’t being met, you may not feel your best — and in some cases, deficiencies can contribute to more serious health concerns.

A vitamin B12 deficiency may contribute to symptoms and conditions such as:⁹

• Mood changes and disturbances
• Fatigue
• Muscle weakness
• Nerve damage
• Anemia
• Intestinal problems
• Cognitive complications, including dementia

On the one hand, dangerously low vitamin B12 levels can pose significant health risks. On the other hand, studies exploring a possible association between cancer and extremely elevated vitamin B12 levels may understandably raise concerns.²

Ultimately, current evidence supports a common-sense approach: when maintained within a healthy range, vitamin B12 plays an essential role in supporting overall health and well-being. If you suspect your vitamin B12 levels may be too high or too low, consider speaking with your healthcare provider about blood testing and strategies for maintaining balanced vitamin B12 levels.

Vitamin B12 plays an important role in energy production, nerve function, and red blood cell formation. If you’re looking for additional nutritional support, Everlywell offers wellness products and supplements designed to help support your overall health and nutrition goals.