Vitamin C: Oral Use
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.
See how we evaluate and rate complementary therapies ›
Improving treatment outcomes
See More- Modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of better survival among women with breast cancer taking vitamin C supplements
- Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of a link between shorter survival, low vitamin C levels, and advanced cancer
- Preliminary evidence of better survival among people with grade 4 malignant glioma with higher intake of vitamin C in their diet
- No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on overall or relapse-free survival among people with acute myeloid leukemia with higher vitamin C levels in a small study
See How can oral vitamin C help you? What the research says ›
Optimizing your body terrain
See MoreGood evidence of benefit
- Good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of lower levels of markers of inflammation among people treated with oral vitamin C
- Good evidence of less oxidative stress (lipid peroxidation) after exercise among healthy volunteers treated with vitamin C supplements
Preliminary evidence of benefit
- Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of a link between vitamin C levels and inflammation; the link likely works in both directions
- Preliminary evidence of a link between plasma vitamin C concentrations and type 2 diabetes or prediabetes
- Preliminary evidence of a higher marker of immune activity among acutely hospitalized patients treated with oral vitamin C
- Preliminary evidence of lower levels of some markers of immune activity during multimodal treatment for esophageal adenocarcinoma among people treated with oral vitamin C
- Preliminary evidence of less DNA damage in peripheral blood lymphocytes among employees working at a thermal power plant treated with oral vitamin C (not specific to cancer)
- Preliminary evidence of a link between neutrophil counts, febrile neutropeniaan abnormally low number of neutrophils in the blood, leading to increased susceptibility to infection, and low vitamin C levels during and after conditioning chemotherapy and hematopoietic stem cell transplantation among people with hematological cancer
- Preliminary evidence of normalized levels of antioxidant enzymes during tamoxifen treatment among postmenopausal women with breast cancer treated with oral vitamin C
- Preliminary evidence of lower oxidative stress after radionuclide therapy (RNT) among people with prostate cancer or neuroendocrine tumors treated with oral vitamin C before RNT
- Preliminary evidence of lower DNA damage in peripheral blood lymphocytes among employees working at a thermal power plant treated with oral vitamin C
- Preliminary evidence of better markers of microbiomethe collection of microbes living on and within your body health (higher microbial alpha diversity and fecal short-chain fatty acids) among healthy volunteers treated with oral vitamin C
- Preliminary evidence of better (normalized) DNA methylation during treatment with DNA methyltransferase inhibitors among people with myeloid cancer treated with oral vitamin C
- Preliminary evidence of higher plasma vitamin C levels and upregulation of several viral defense genes in malignant myeloid cells but not T cells during treatment with DNA methyltransferase inhibitors among people with myeloid cancers treated with oral vitamin C
No evidence of benefit
- No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on oxidative stressan imbalance between free radicals and antioxidants in your body in which antioxidant levels are lower than normal; this imbalance can cause harmful oxidation reactions in your body chemistry among people with type 2 diabetes treated with vitamin C
- No evidence of an effect on blood sugar and insulin among people with type 2 diabetes treated with vitamin C overall, although weak evidenceone or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects (this is the CancerChoices definition; other researchers and studies may define this differently) of a possible effect at a dose of 1000 mg vitamin C per day
See How can oral vitamin C help you? What the research says ›
Managing side effects and promoting wellness
See MoreGood evidence of benefit
- Good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of fewer symptoms of mucosal irritation induced by Lugol chromoendoscopy among people with esophageal dysplasia and carcinoma treated with a vitamin C solution spray
Modest evidence of benefit
- Modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of less anxiety related to stress among people treated with oral vitamin C (not specific to cancer)
- Modest evidence of higher fat-free mass among middle-aged and older people with higher dietary intakes or plasma levels of vitamin C (not specific to cancer)
- Modest evidence of lower fracture risk among men, but not women, with the highest plasma vitamin C concentrations (not specific to cancer)
- Modest evidence of lower blood pressure related to stress or exercise among people treated with oral vitamin C (not specific to cancer)
- Modest evidence of less depression among people treated with oral vitamin C (not specific to cancer)
Preliminary evidence of benefit
- Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of less toxicity and fewer cancer therapy delays after 6 months among children with acute lymphoblastic leukemia with higher vitamin C in their diets
- Preliminary evidence of higher body weight during chemotherapy among people with acute myeloid leukemia treated with vitamin C supplements
- Preliminary evidence of better quality of life scores during radiotherapy among people with head and neck cancer treated with chewable ascorbic acid tablets
- Preliminary evidence of less change in body composition during exercising among elderly women treated with oral vitamin C (not specific to cancer)
- Preliminary evidence of lower measures of pain and less nausea and vomiting after surgery among adults treated with oral vitamin C 1 hour before surgery (not specific to cancer)
- Preliminary evidence of a higher rate of penile-vaginal intercourse among healthy young adults treated with oral vitamin C
No evidence of benefit
- No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on appetite among people with advanced cancer treated with high-dose oral vitamin C in a small trial
- No evidence of an effect on pain among people with advanced cancer treated with 10 g oral vitamin C in a mid-sized study
- No evidence of an effect on strength among people with advanced cancer treated with 10 g oral vitamin C in a mid-sized study
- No evidence of an effect on muscle soreness or muscle strength after a single exercise session among healthy volunteers treated with vitamin C supplements in a combined analysis of studies
See How can oral vitamin C help you? What the research says ›
Reducing cancer risk
See MoreGood evidence of benefit
- Good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of lower risk of lung cancer among people with higher levels of vitamin C intake from diet, but no evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on risk from vitamin C supplements
Modest evidence of benefit
- Modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of a link between low vitamin C levels and risk of cancer as a whole
- Modest evidence of lower risk of recurrence among people with breast cancer taking vitamin C supplements; also see weak evidenceone or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects (this is the CancerChoices definition; other researchers and studies may define this differently) of higher risk of recurrence and death among people with breast cancer taking antioxidants as a whole in Safety and precautions ›
- Modest evidence of greater regression of precancerous lesions among people with multifocal atrophic gastritis treated with oral vitamin C
- Modest evidence of lower risk of esophageal cancer or Barrett’s esophagus—a risk factor for esophageal cancer—among people with the highest levels of dietary vitamin C intake
Preliminary evidence of benefit
- Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of a link between low vitamin C levels and breast cancer risk
- Preliminary evidence of lower risk of colon cancer among people with higher diet-derived circulating levels of vitamin C
- Preliminary (conflicting) evidence of an effect on risk of colorectal cancer among people with genetically predicted higher levels of circulating vitamin C levels
- Preliminary evidence of lower risk of small intestine cancer among people with genetically predicted higher levels of circulating vitamin C
- Preliminary evidence of a link between low vitamin C levels and risk of gynecologic cancer; we don’t know if low vitamin C levels contribute to cancer risk, or if having cancer leads to low vitamin C levels, or if the link works in both directions
- Preliminary evidence of a link between low vitamin C levels and risk of leukemia; we don’t know if low vitamin C levels contribute to cancer risk, or if having cancer leads to low vitamin C levels, or if the link works in both directions
- Preliminary evidence of moderately lower risk of melanoma among people with the highest intake of vitamin C in their diets
- Preliminary evidence of a link between lower vitamin C levels and risk of mesothelioma; we don’t know if low vitamin C levels contribute to mesothelioma risk, or if having mesothelioma leads to low vitamin C levels, or if the link works in both directions
- Preliminary evidence of a link between lower vitamin C levels and risk of multiple myeloma; we don’t know if low vitamin C levels contribute to multiple myeloma risk, or if having multiple myeloma leads to low vitamin E levels, or if the link works in both directions
No evidence of benefit
- No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on risk of cancer as a whole among people treated with oral vitamin C in large controlled studies
- No evidence of an effect on risk of urothelial cell carcinoma among people with higher plasma vitamin C levels in a large study
- No evidence of an effect on breast cancer risk among people with higher levels of vitamin C intake from diet and/or supplements in a combined analysis of studies
- No evidence of an effect on rectal cancer risk among people with higher levels of vitamin C intake from diet
- No evidence of an effect on risk of esophageal, gastric, or liver cancers among people taking oral vitamin C in a combined analysis of studies
- No evidence of an effect on risk of esophageal, stomach, or liver cancer among people with higher levels of vitamin C in several combined analyses of studies
- No evidence of an effect on risk of sunburn—a risk factor for skin cancer—or cutaneous squamous cell carcinoma among people with higher intake of vitamin C
- No evidence of an effect on risk of cutaneous squamous cell carcinoma among non-Hispanic whites with higher self-report vitamin C intake
- No evidence of an effect on risk of ovarian cancer among women with higher dietary vitamin C intake in a large combined analysis of studies
- No evidence of an effect on risk of pancreatic cancer among people taking oral vitamin C in a combined analysis of studies
- No evidence of an effect on risk of pancreatic cancer among people with higher diet-derived circulating levels of vitamin C in a combined analysis of studies
- No evidence of an effect on prostate cancer risk among people with higher levels of vitamin C intake from diet and/or supplements in very large studies
- No evidence of an effect on prostate cancer risk among people with genetically predicted higher levels of circulating vitamin C levels in a very large analysis
See How can oral vitamin C help you? What the research says ›
Use by integrative oncology experts
See More- Used in several (at least 4) of our program sources
- Not mentioned in integrative cancer clinical practice guidelines
Safety
See More- Higher risk of liver cancer or melanoma among people with higher intake of vitamin C, sometimes with other antioxidants, and possibly slightly higher risk of recurrence or diagnosis of breast cancer, rectal cancer, and gastrointestinal cancer
- Potential to interfere with chemotherapy and radiation therapy
- Potential to cause excess bleeding during surgery or surgical procedures
- May cause side effects, which at high doses may be serious
- May interact with other medications
Affordability and access
See More- Available in most drug stores without a prescription
- Low cost (less than $500 US/year)
Keep reading about oral vitamin C
Author
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.
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.
Reviewer
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 Series, Journal of Alternative & Complementary Medicine and Natural Medicine Journal.
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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References[+]
| 1 | The Nutrition Source. Vitamin C. Harvard T. H. Chan School of Public Health. March 2023. Viewed April 10, 2023. |
|---|---|
| 2 | Kaźmierczak-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. |
| 3 | Schectman 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. |
| 4 | Milbar 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. |