Vitamin C: Oral Use - CancerChoices

Vitamin C, available in several foods and dietary supplements, shows some anticancer effects, including better survival among people with breast cancer.

Oral vitamin C at a glance

Vitamin C, also called ascorbic acid or ascorbate, is an essential nutrient for growth, development, and healing. A deficiency is linked to increased risk of several diseases, including cancer as a whole and many types of cancer. 

Humans cannot produce vitamin C, so we need to get it from foods or supplements. Although vitamin C is usually associated with citrus fruits, it’s found in many other foods:

  • Peppers
  • Berries
  • Potatoes
  • Tomatoes
  • Spinach
  • Parsley
  • Cruciferous vegetables, including cabbage, Brussels sprouts, and broccoli 

Vitamin C dissolves in water and is destroyed by high heat. Therefore, vitamin C levels will be lower if foods are cooked, especially if cooked in water.1The Nutrition Source. Vitamin C. Harvard T. H. Chan School of Public Health. March 2023. Viewed April 10, 2023.

A diet high in refined foods and processed sugar can inhibit the absorption of vitamin C,2Kaźmierczak-Barańska J, Boguszewska K, Adamus-Grabicka A, Karwowski BT. Two faces of vitamin C—antioxidative and pro-oxidative agent. Nutrients. 2020 May 21;12(5):1501. and people who smoke are at higher risk of vitamin C deficiency.3Schectman G, Byrd JC, Gruchow HW. The influence of smoking on vitamin C status in adults. American Journal of Public Health. 1989 Feb;79(2):158-62. People with leukemia are also at risk of vitamin C deficiency.4Milbar HC, Caplan A et al. Vitamin C deficiency in patients with acute myeloid leukemia: a case series and review of the literature. Blood Advances. 2023 Oct 10;7(19):5780-5783. 

Oral vitamin C is also available as a dietary supplement. Oral intake of vitamin C, from either diet or supplements, shows some anticancer effects, including better survival among people with breast cancer. However, research also shows that higher intake of vitamin C is linked to higher risk of liver cancer or melanoma and possibly slightly higher risk of recurrence or diagnosis of breast cancer, rectal cancer, and gastrointestinal cancer. High oral doses can lead to serious side effects. Even though vitamin C supplements are readily available at low cost, we recommend professional guidance in using supplements.

Intravenous vitamin C is another therapy used among people with cancer. We review it separately due to its different benefits, safety issues, access, and affordability.

CancerChoices ratings for oral vitamin C

We rate oral vitamin C on seven attributes, with 0 the lowest rating and 5 the highest. We rate the strength of the evidence supporting the use of oral vitamin C for a medical benefit, such as improving treatment outcomes or managing side effects.

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Improving treatment outcomes

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Optimizing your body terrain

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Managing side effects and promoting wellness

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Reducing cancer risk

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Use by integrative oncology experts

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Affordability and access

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Keep reading about oral vitamin C


Nancy Hepp, MS

Lead Researcher
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Ms. Hepp is a researcher and communicator who has been writing and editing educational content on varied health topics for more than 20 years. She serves as lead researcher and writer for CancerChoices and also served as the first program manager. Her graduate work in research and cognitive psychology, her master’s degree in instructional design, and her certificate in web design have all guided her in writing and presenting information for a wide variety of audiences and uses. Nancy’s service as faculty development coordinator in the Department of Family Medicine at Wright State University also provided experience in medical research, plus insights into medical education and medical care from the professional’s perspective.

Nancy Hepp, MS Lead Researcher

Laura Pole, MSN, RN, OCNS

Senior Clinical Consultant
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Laura Pole is senior clinical consultant for CancerChoices. Laura is an oncology clinical nurse specialist who has been providing integrative oncology clinical care, navigation, consultation, and education services for over 40 years. She is the co-creator and co-coordinator of the Integrative Oncology Navigation Training at Smith Center for Healing and the Arts in Washington, DC. Laura also manages the “Media Watch Cancer News That You Can Use” listserv for Smith Center/Commonweal. In her role as a palliative care educator and consultant, Laura has served as statewide Respecting Choices Faculty for the Virginia POST (Physician Orders for Scope of Treatment) Collaborative as well as provided statewide professional education on palliative and end-of-life care for the Virginia Association for Hospices and Palliative Care.

For CancerChoices, Laura curates content and research, networks with clinical and organizational partners, brings awareness and education of integrative oncology at professional and patient conferences and programs, and translates research into information relevant to the patient experience as well as clinical practice.

Laura sees her work with CancerChoices as a perfect alignment of all her passions, knowledge and skills in integrative oncology care. She is honored to serve you.

Laura Pole, MSN, RN, OCNS Senior Clinical Consultant


Jen Green, ND, FABNO

Naturopathic oncologist and CancerChoices advisor
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Dr. Green is a naturopathic physician who is board-certified in naturopathic oncology (FABNO). Dr. Green is also a cofounder/research director for Knowledge in Integrative Oncology Website, a nonprofit website that harvests up-to-date research in integrative oncology to support evidence-informed decision making. Dr. Green has published scientific articles in journals such as the American Urology Association Update SeriesJournal of Alternative & Complementary Medicine and Natural Medicine Journal.

Jen Green, ND, FABNO Naturopathic oncologist and CancerChoices advisor

Last update: May 7, 2024

Last full literature review: January 2023

CancerChoices provides information about integrativein cancer care, a patient-centered approach combining the best of conventional care, self care, and evidence-informed complementary care in an integrated plan cancer care. We review complementaryin cancer care, complementary care involves the use of therapies intended to enhance or add to standard conventional treatments; examples include supplements, mind-body approaches such as yoga or psychosocialtherapy, and acupuncture therapies and self carelifestyle actions and behaviors that may impact cancer outcomes; examples include eating health-promoting foods, limiting alcohol, increasing physical activity, and managing stress practices to help patients and professionals explore and integrate the best combination of conventionalthe cancer care offered by conventionally trained physicians and most hospitals; examples are chemotherapy, surgery, and radiotherapy and complementary therapies and practices for each person.

Our staff have no financial conflicts of interest to declare. We receive no funds from any manufacturers or retailers gaining financial profit by promoting or discouraging therapies mentioned on this site.

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