Can Vitamin B12 Deficiency Be a Sign of Cancer?

Your body needs a variety of nutrients to function. Having too little (a deficiency) of a specific vitamin or mineral can lead to health problems.

Researchers have reported lower vitamin B12 levels in some people with cancer. But it isn’t clear whether the deficiency is related to the cancer or caused by something else.

“Any micronutrient deficiency is going to affect your body. There could be a link between B12 and cancer, but we don’t have that definitive answer yet,” said Patty McDonnell, RD, CSO, CD, FAND, a clinical oncology nutrition advisor at Fred Hutch Cancer Center.

What is vitamin B12?

Vitamin B12 is also called cobalamin and supports the body in several ways. It is essential to help form red blood cells, produce cellular DNA (genetic material in cells), and keep nerve cells healthy.

The body can’t make vitamin B12 on its own. People have to get it from eating certain foods and possibly taking supplements. Vitamin B12 is found in animal and dairy products such as fish, seafood, meat, poultry, milk, cheese, and yogurt. Some fortified foods have B12 added to them.

What can cause vitamin B12 deficiency?

A B12 deficiency can happen for a few reasons. Either a person isn’t getting enough B12 in their diet, their body isn’t absorbing it well, or their body needs more than it has. A vitamin B12 deficiency, however, is not considered a sign of cancer.

“Vitamin B12 needs the stomach and intestines to work together to absorb it properly. Any health condition that affects these organs makes it harder to process B12,” said McDonnell.

Causes and risk factors for vitamin B12 deficiency include:

• Not eating enough food that contains B12: Older adults are more at risk due to reduced ability to absorb B12 from food. People who eat vegan diets have a higher risk as well.
• Digestive problems related to gastritis, Crohn’s disease, or celiac disease
• Having gastric bypass weight-loss surgery
• Pernicious anemia, an autoimmune condition that can prevent B12 absorption
• Surgical removal of all or part of the stomach (gastrectomy)
• Poor nutrition and stomach damage from heavy alcohol use
• Specific medications, such as metformin for type 2 diabetes and proton pump inhibitors for heartburn or reflux issues
• Certain family cancer syndromes
• Cancers that affect B12 absorption, such as stomach, pancreatic, and small intestine cancers
• Pregnancy and breastfeeding because of the increased need for B12 to support the baby’s growth

What is the connection between vitamin B12 deficiency and cancer?

Researchers have explored how both low and high vitamin B12 levels might be related to cancer. The study results are mixed.

Some studies have found lower levels of vitamin B12 in people with breast, cervical, liver, stomach, and colorectal cancers. However, this does not mean a B12 deficiency causes cancer. Cancers that start in the digestive system often affect how the stomach and intestines work, possibly contributing to B12 deficiency.

Along with cancer itself, cancer treatment can often affect B12 levels. For example, chemotherapy can damage cells along the digestive tract. Radiation therapy given in the lower abdomen (pelvis) can cause cell damage to the intestines. Both of these situations can cause B12 levels to drop.

Researchers have also reported high vitamin B12 levels in some people with cancer, including blood, stomach, lung, pancreatic, and colorectal cancers. But they aren’t sure whether elevated B12 levels are related to the cancer itself, another health problem, or something else.

“More research is needed to learn whether and how vitamin B12 is connected to cancer. If you have concerns about your B12 levels, talk with a registered dietitian or your healthcare provider,” said Heather Greenlee, ND, PhD, MPH, an American Society of Clinical Oncology (ASCO) expert and medical director of the Integrative Medicine Program at Fred Hutch.

Signs and symtoms of a vitamin B12 deficiency

A vitamin B12 deficiency is diagnosed with a blood test. Current guidelines do not recommend routine screening for B12 deficiency. Instead, testing is often recommended for people who have signs and symptoms of a B12 deficiency, such as: 

• Anemia
• Fatigue
• Memory problems or mental health problems
• Balance issues
• An inflamed tongue
• Numbness and tingling in the hands and feet (called neuropathy)

Risk factors for a vitamin B12 deficency can be related to age, nutrition, digestive problems, medications, and personal and family health history.

What can you do to raise your vitamin B12 levels?

If you have a vitamin B12 deficiency, your doctor might order additional tests. The results will help determine the best options for getting your B12 levels back to what’s normal for you. Keeping vitamin B12 levels in a recommended range can help prevent long-term health problems.

The most common recommendation is to eat more foods that contain B12, with meat, fish, and dairy being the best natural sources. People who follow a vegan diet may need to consume more fortified foods, like certain cereals, nutritional yeast products, and plant-based milks.

“Get vitamin B12 through whole foods if you can. That way you benefit from all the other nutrients in the foods as well,” Dr. Greenlee said.

If diet changes are not enough, your doctor may recommend a daily multivitamin with B12. People who cannot digest B12 can take a supplement that is placed and absorbed under the tongue (sublingual), inhaled through the nose, or given as a shot injected into muscle. These methods allow the vitamin to be absorbed directly into the bloodstream.

More vitamin B12 is not necessarily better, though. “The daily recommended amount of B12 for most adults is 2.4 micrograms,” said McDonnell. “Most multivitamins and supplements contain much more than that. There’s no need to exceed what your doctor or registered dietitian recommends.”

How long does it take for vitamin B12 levels to return to normal?

B12 levels often improve quickly after treatment starts. Many people notice improvement in their symptoms within weeks, although neuropathy symptoms can take months to improve. Results and how long you need treatment depend on the cause of the deficiency, its severity, how long you’ve had it, and which form of B12 you take.

“Vitamin B12 deficiency usually requires long-term treatment because the cause often doesn’t go away,” McDonnell said

Vitamins and minerals are only one part of a nutritious diet, however. “Supplements are not a silver bullet for lowering your cancer risk or treating cancer,” Dr. Greenlee said. “It’s important to focus on the big picture of achieving and maintaining a healthy diet, instead of just taking dietary supplements.”

Learn more from the American Cancer Society:

• Guideline for Diet and Physical Activity for Cancer Prevention
• Is Anemia a Sign of Cancer?
• Are Dietary Supplements Safe?

Dr. Greenlee is a member of ASCO’s Patient Information Advisory Committee and ASCO’s Evidence-Based Medicine Committee.