Chemotherapy — the use of powerful drugs to destroy cancer cells and prevent cancer from spreading — can come with many side effects, including fatigue, numbness and tingling and brain fog, according to the American Cancer Society (ACS). And a deficiency in vitamin B12 could make these and other symptoms worse.
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"B12 plays a crucial role in energy and the ability to build new blood cells," Megan Kruse, MD, an oncologist at the Cleveland Clinic, tells LIVESTRONG.com. Your B12 level can be measured during treatment to keep an eye on your range, Dr. Kruse says.
Normal values for vitamin B12 can range from 160 to 950 picograms per milliliter, according to Mount Sinai. You may be considered deficient even at the low end of that range; below about 170 to 250 pg/mL is usually deemed a vitamin B12 deficiency, according to the Office of Dietary Supplements (ODS). Additional tests can be performed to confirm whether you have vitamin B12 deficiency or not when your vitamin B12 level is in the low-normal range.
Most adults should get about 2.4 micrograms of vitamin B12 per day, about the amount in a 3-ounce serving of canned tuna, according to the ODS. And it may be safest to get that daily amount from food alone, according to December 2019 research in the Journal of Clinical Oncology. The study found patients with breast cancer who took vitamin B12 supplements during chemotherapy had a greater risk of cancer recurrence or death than women who didn't take B12.
However, Dr. Kruse says, you may need more B12 than what you get from food alone to prevent a deficiency if you are a vegetarian (since the vitamin is most commonly found in animal products) or undergoing chemotherapy treatment. And if you need additional vitamin B12 during chemo, you may be a good candidate for a B12 injection, she adds.
Always consult your physician or oncologist before supplementing with B12 or other vitamins to determine your personal risks and potential benefits during chemotherapy.
Here are three ways vitamin B12 is thought to possibly help people undergoing chemo.
Since chemotherapy destroys any cells that are growing or multiplying rapidly, even healthy cells, it may reduce your overall red blood cell count, which can make you feel tired. Because vitamin B12 is crucial in red blood cell production, a deficiency can further increase fatigue.
"Vitamin B12 is one of those vitamins that makes patients feel good," Dr. Kruse says. "Often times supplementing with it will help patients feel better and boost their energy." B12 supplements may increase red blood cell production, helping improve symptoms associated with fatigue, according to Michigan Medicine.
Chemotherapy can cause damage to nerve tissue called peripheral neuropathy, which may result in pain, tingling and numbness, especially in the hands and feet. Peripheral neuropathy from chemo can last for months, years or even for the rest of your life, according to the ACS.
Some research suggests that B vitamin supplementation may help prevent chemotherapy-induced peripheral neuropathy, but more research is needed to determine how well it works and how much to take, according to an October 2017 review published in Current Oncology Reports.
Many patients will experience brain fog — sometimes called "chemo brain" — during chemotherapy. This can involve issues with concentration and memory, both during and after treatment, according to the ACS.
Supplementing with vitamin B12 has long been thought to improve cognitive function. However, research to date has been inconclusive and more studies are needed to assess the overall effect of B12 on brain fog, according to Memorial Sloan Kettering Cancer Center.
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- Michigan Medicine: "Vitamin B12 Deficiency Anemia"
- American Cancer Society: "Chemo Brain"
- Office of Dietary Supplements: "Vitamin B12"
- American Cancer Society: "Chemotherapy Side Effects"
- Mount Sinai: "Vitamin B12 Level"
- Current Oncology Reports: "B Vitamin Complex and Chemotherapy-Induced Peripheral Neuropathy"
- American Cancer Society: "What Is Peripheral Neuropathy?"
- Memorial Sloan Kettering Cancer Center: "Vitamin B12"
- Journal of Clinical Oncology: "Dietary Supplement Use During Chemotherapy and Survival Outcomes of Patients With Breast Cancer Enrolled in a Cooperative Group Clinical Trial"