Table of ContentsView AllTable of ContentsReasons to Take VitaminsVitamin D and CancerReasons Not to Take VitaminsConsiderations
Table of ContentsView All
View All
Table of Contents
Reasons to Take Vitamins
Vitamin D and Cancer
Reasons Not to Take Vitamins
Considerations
Taking vitamins or other supplements duringcancertreatment may have benefits, but there can also be risks. Cancer fatigue may be one reason people turn to vitamins and other supplements or because they believe they have anti-cancer and anti-toxicity properties.
However, the effects of taking vitamin and mineral dietary supplements during cancer treatment are uncertain and some might interfere with the effectiveness of chemotherapy or other cancer therapies.
Never take a vitamin, mineral, or antioxidant supplement without first consulting your healthcare provider, as this can be dangerous for some people with cancer.
Verywell / Ellen Lindner
When Do Oncologists Recommend Vitamins?
There are several reasons why your healthcare provider may recommend dietary supplements.
To Treat Nutrition Deficiencies
With side effects like loss of appetite and nausea that are common with cancer, nutritional deficiencies can occur. Talk to your healthcare provider about this possibility.
Some researchers have theorized that supplementation could help reducecancercachexia. Cachexia is a syndrome of unintentional weight loss, muscle wasting, and decreased appetite that affects up to 50% to 80% of people with advanced cancer.
It is estimated that cachexia contributes directly to 20% of cancer deaths.Cancer cachexia is extremely challenging to treat and most nutrition supplements have not been found to aid in this syndrome. However, there is some evidence that omega-3 fatty acids may be helpful.
To Reduce Cancer Fatigue
A 2017 review concluded the following may help with energy levels in cancer survivors:
Another study found that an extract of a South American plant called guarana—along with a healthy diet—helped reduce cancer-related fatigue in people being treated for breast cancer.
To Prevent a Second Cancer
Since cancer treatments such as chemotherapy and radiation therapy predispose survivors to other cancers, the hope has been that the risk of a second cancer could be reduced with the use of antioxidant supplements.
Just as supplements (as opposed to dietary antioxidants) have not shown consistent results in preventing cancer, there is not much evidence that these supplements would help prevent a second cancer in survivors.
To Decrease Toxicity of Treatments
Studies have been mixed concerning antioxidants increasing or reducing the toxicity of chemotherapy, but some research suggests they may improve the quality of life for some people during cancer treatment. However, the research results are mixed on whether antioxidants are beneficial or harmful during chemotherapy.
To Increase Life Expectancy
An oft-quoted study supporting the use of vitamin supplements during cancer treatment showed an increase in the length of survival. This 2009 study revealed a longer-than-expected median survival time, with 76% of the patients living longer than was predicted (median increase in survival of 5 months).
It’s important to note that this was a very small study (41 patients) conducted with people considered to have end-stage cancer who had a predicted life expectancy of only 12 months. These patients were treated with a supplement of coenzyme Q10, vitamins A, B, and C, selenium, folic acid, and for those without lung cancer, beta-carotene.
For several reasons, vitamin D deserves special consideration concerning its role in cancer treatment.
We think of fortified milk as being a source of vitamin D, but at about 120 IU per glass, it would require drinking almost seven glasses per day just to reach the 800 IU recommended for a 70-year-old person (much less the dose studied in cancer prevention studies).
The sun is a good source of vitamin D, requiring only short amounts of time with arms and face exposed to absorb upwards of 5,000 IU. That is, you need to live in a region where you can be outside with your arms and face exposed and the angle of the sun at your latitude allows the absorption of vitamin D-producing rays. This can be a problem in northern climates.
For this reason, many healthcare providers recommend a supplement of vitamin D3.
Who Should Take a Vitamin D Supplement?
A simple and inexpensive blood test can provide you and your healthcare provider with a measure of your blood level of vitamin D. While this won’t tell you what your total body “store” of vitamin D is, it can be used to determine if a supplement is needed and guide treatment.
It is estimated that almost 20% of middle-aged and older adults in the U.S. are vitamin D deficient and 34% have vitamin D insufficiency.
Importance of Vitamin D
Vitamin D is not an antioxidant. It functions more like a hormone than a vitamin in the body.
There have been many studies that have evaluated the role of vitamin D both in cancer prevention and cancer treatment.
Since some cancer treatments predispose to osteoporosis, and vitamin D aids calcium absorption, an adequate vitamin D level may also affect the quality of life for some cancer patients.
Vitamin D supplementationmay also help with cancer fatigue. One small study showed cancer patients with higher vitamin D levels reported less fatigue and improved well-being.
Even though much of the research shows a positive role of vitamin D for some people with cancer, it’s important to talk to your healthcare provider before using a supplement. Your healthcare provider will want to monitor your levels to see if they change if you begin a supplement.
The normal range of values may not be the ideal range for someone with cancer. For example, the reference range for normal vitamin D levels is 30–80. Yet some studies suggest that a level of 50 is better than a level of 31.
Vitamin D supplementation is not for everyone. There are potential side effects, including, kidney stones, if levels are too high.
Vitamin B12Like vitamin D, vitamin B12 is not an antioxidant, and it’s thought that many older adults are deficient. But as with other vitamins, it’s important to talk to your healthcare provider before taking supplements.
Vitamin B12
Like vitamin D, vitamin B12 is not an antioxidant, and it’s thought that many older adults are deficient. But as with other vitamins, it’s important to talk to your healthcare provider before taking supplements.
Why Your Oncologist May Not Recommend Vitamins
There are many types of cancer, and even with a single type of cancer, there are tremendous differences. Add in each unique person, with their own body characteristics and other medical conditions, and it’s easy to see why taking supplements during cancer treatment is very complex.
There are several reasons why your oncologist may recommend that you avoid vitamin or mineral supplements. Sometimes the particular reason may not be obvious (such as knowing the vitamins that may affect blood test results with cancer), and it’s important to ask your healthcare provider what you should avoid and why. These are some reasons to avoid vitamin supplements:
Possible Interference With the Benefits of Treatment
One of the main reasons oncologists don’t recommend vitamin and mineral supplements or antioxidant formulas is they could counteract the effects of chemotherapy or radiation therapy.
Interaction With Chemotherapy
Vitamin C may reduce the effectiveness of some chemotherapy agents, including vincristine, doxorubicin, methotrexate, cisplatin, and imatinib.So far, these effects have been seen only in some laboratory and animal studies.
How vitamin C is given may also influence its effectiveness and risks. Some studies of intravenous (IV) vitamin C use in people with cancer showed it improved quality of life and reduced cancer-related side effects.
Vitamin C and Hormonal Therapy
Studies looking at human breast cancer cells in a lab have found that vitamin C decreased the effectiveness of tamoxifen. In these studies, it was thought that vitamin C interfered withapoptosis(cell death) in cancer cells.
Vitamin C and Targeted Therapy
Targeted therapies are newer cancer treatments that target specific pathways in the growth of cancer cells. Inanimal studies, vitamin C appeared to reduce the anti-cancer activity of the targeted therapy Velcade (bortezomib). Velcade is used for people with multiple myeloma and some types of lymphoma.
Some of the risks may be more theoretical. A 2007 review of studies from 1983 to 2005 found no evidence that antioxidant supplements interfered with chemotherapy, and some researchers believe that antioxidants may help to protect normal cells without interfering with the effectiveness of cancer therapy.
This review included studies usingglutathione,vitamin A, vitamin C, vitamin E, ellagic acid,selenium,beta-carotene, melatonin, andN-acetylcysteine. The review concluded that antioxidants may improve tumor response to treatment and survival rates while also aiding patients’ tolerance to treatment.
Another systematic review found evidence that using antioxidants with chemotherapy resulted in less toxicity, allowing people to complete full doses of therapy. The exception was one study that showed an increase in toxicity in those using a vitamin A supplement. This review evaluated studies usingN-acetylcysteine, vitamin E, selenium, L-carnitine,Coenzyme Q10, and ellagic acid.
Interaction With Other Medications
There are many examples of possible interactions, but a simple example is that of vitamin E, which could potentially increase the risk of bleeding in people who are taking the blood thinner warfarin.
Interactions That Affect Blood Tests
Some vitamins such as biotin (vitamin B7) may interfere with the assays done to provide some laboratory results. Of note is thatbiotinmay be present in many combination vitamin supplements.
Dietary Sources vs. Supplements
We don’t have as many studies looking at the use of antioxidants during cancer treatment, but the use of these supplements with the goal of cancer prevention has revealed some interesting findings.
For example, a high dietary intake of beta-carotene was associated with a lower risk of developing lung cancer, but a review of studies looking at the use of a beta-carotene supplement found that the risk of lung cancer was increased, especially in smokers.
Findings were similar with prostate cancer: Dietary vitamin E consumption is associated with a lower risk, but a study evaluating vitamin E supplements found an increased risk.
In general, the rule for getting vitamins and minerals during cancer treatment is “food first.”
Theories have been proposed to explain why supplements may increase cancer risk. Perhaps there are phytochemicals (plant-based chemicals) in food aside from beta-carotene (or other antioxidants) that are responsible for the cancer prevention properties.
Another theory that’s been proposed is that receiving one antioxidant as a supplement may result in the body absorbing less or using less, of another important antioxidant.
Sometimes taking a supplement for one concern may raise another. An example is a study in which people with melanoma were treated with selenium. Researchers found that the supplement was associated with a lower risk of developing a second cancer in the lungs, colon, or prostate, but was also associated with an elevated risk of diabetes.
Most oncologists recommend eating a healthy diet and do not believe the antioxidants derived from foods pose a threat to the effectiveness of cancer treatments.
Method of Study
Interpreting some of the information on antioxidants during cancer treatment is difficult for many reasons, one of which is the different methods used.
There are also special cases that can’t be addressed when studies look at the general population. For instance:
The role of vitamins and antioxidants can also vary depending on particular treatments. For example, vitamin C may reduce the effectiveness of radiation but may also reduce the toxicity.
Considerations for Taking Vitamins
If your oncologist does recommend a supplement, there are a few things to keep in mind.
Summary
Vitamin and mineral supplements during cancer treatment may have risks as well as benefits. Risks include counteracting the effects of chemotherapy or radiation, interfering with targeted therapies, and interacting with other medications. Benefits may include improving nutritional deficiencies, cancer fatigue, and cachexia.
Talk with your oncologist before taking any supplements to understand the potential risks or benefits associated with the type of cancer you have and the treatments you are receiving.
28 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Harvie M.Nutritional supplements and cancer: potential benefits and proven harms.Am Soc Clin Oncol Educ Book. 2014:e478-486. doi:10.14694/EdBook_AM.2014.34.e478
National Center for Complementary and Integrative Health.Cancer and complementary health approaches: what you need to know.
von Haehling S, Anker MS, Anker SD.Prevalence and clinical impact of cachexia in chronic illness in Europe, USA, and Japan: facts and numbers update 2016.J Cachexia Sarcopenia Muscle. 2016;7(5):507-509. doi:10.1002/jcsm.12167
Ni J, Zhang L.Cancer cachexia: definition, staging, and emerging treatments.Cancer Manag Res. 2020;12:5597-5605. doi:10.2147/CMAR.S261585
Garcia JM, Shamliyan TA.Omega-3 fatty acids in patients with anorexia-cachexia syndrome associated with malignancy and its treatments.Am J Med. 2017;130(10):1151-1155. doi:10.1016/j.amjmed.2017.03.066
Inglis JE, Lin PJ, Kerns SL, et al.Nutritional interventions for treating cancer-related fatigue: a qualitative review.Nutr Cancer. 2019;71(1):21-40. doi:10.1080/01635581.2018.1513046
American Cancer Society.Can I do anything to prevent cancer recurrence?.
Hertz N, Lister RE.Improved survival in patients with end-stage cancer treated with coenzyme Q(10) and other antioxidants: a pilot study.J Int Med Res. 2009;37(6):1961-1971. doi:10.1177/147323000903700634
National Institutes of Health Office of Dietary Supplements.Vitamin D: fact sheet for health professionals.
Wang TY, Wang HW, Jiang MY.Prevalence of vitamin D deficiency and associated risk of all-cause and cause-specific mortality among middle-aged and older adults in the United States.Front Nutr. 2023;10:1163737. doi:10.3389/fnut.2023.1163737
Martínez-Alonso M, Dusso A, Ariza G, Nabal M.Vitamin D deficiency and its association with fatigue and quality of life in advanced cancer patients under palliative care: a cross-sectional study.Palliat Med. 2016;30(1):89-96. doi:10.1177/0269216315601954
Vincenti A, Bertuzzo L, Limitone A, D’Antona G, Cena H.Perspective: practical approach to preventing subclinical B12 deficiency in elderly population.Nutrients. 2021;13(6):1913. doi:10.3390/nu13061913
Jung AY, Cai X, Thoene K, et al.Antioxidant supplementation and breast cancer prognosis in postmenopausal women undergoing chemotherapy and radiation therapy.Am J Clin Nutr. 2019;109(1):69-78. doi:10.1093/ajcn/nqy223
Memorial Sloan Kettering Cancer Center.Vitamin C purported benefits, side effects, and more.
National Cancer Institute.Intravenous vitamin C (PDQ) - patient version.
Perrone G, Hideshima T, Ikeda H, et al.Ascorbic acid inhibits antitumor activity of bortezomibin vivo.Leukemia. 2009;23(9):1679-1686. doi:10.1038/leu.2009.83
Block KI, Koch AC, Mead MN, Tothy PK, Newman RA, Gyllenhaal C.Impact of antioxidant supplementation on chemotherapeutic efficacy: a systematic review of the evidence from randomized controlled trials.Cancer Treat Rev. 2007;33(5):407-418. doi:10.1016/j.ctrv.2007.01.005
Singh K, Bhori M, Kasu YA, et al.Antioxidants as precision weapons in war against cancer chemotherapy induced toxicity—exploring the armoury of obscurity.Saudi Pharm J. 2018;26(2):177-190. doi:10.1016/j.jsps.2017.12.013
Drugs.com.Drug Interactions between vitamin E and warfarin.
Food and Drug Administration.FDA in Brief: FDA reminds patients, health care professionals and laboratory personnel about the potential for biotin interference with certain test results, especially specific tests to aid in heart attack diagnoses.
Kordiak J, Bielec F, Jabłoński S, Pastuszak-Lewandoska D.Role of beta-carotene in lung cancer primary chemoprevention: a systematic review with meta-analysis and meta-regression.Nutrients. 2022;14(7):1361. doi:10.3390/nu14071361
Kristal AR, Darke AK, Morris JS, et al.Baseline selenium status and effects of selenium and vitamin E supplementation on prostate cancer risk.J Natl Cancer Inst. 2014;106(3):djt456. doi:10.1093/jnci/djt456
Salehi B, Martorell M, Arbiser JL, et al.Antioxidants: positive or negative actors?.Biomolecules. 2018;8(4):124. doi:10.3390/biom8040124
Quinn J, Gerber B, Fouche R, Kenyon K, Blom Z, Muthukanagaraj P.Effect of high-dose vitamin C infusion in a glucose-6-phosphate dehydrogenase-deficient patient.Case Rep Med. 2017;2017:5202606. doi:10.1155/2017/5202606
Lands R, Isang E.Secondary hemochromatosis due to chronic oral iron supplementation.Case Rep Hematol. 2017;2017:2494167. doi:10.1155/2017/2494167
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