Close this search box.

Vitamin C – L-ascorbic acid

Vitamin C chemical formula and representation

Vitamin C is a water-soluble vitamin naturally present in some foods that can also be added to others or taken as a dietary supplement. Humans, unlike most animals, lack the ability to synthesize Vitamin C from glucose endogenously (only humans, primates and guinea pigs do not produce their own Vitamin C), therefore it has necessarily to be part of the diet1.

The main biological functions of Vitamin C are2:

  • Physiological antioxidant 
  • Regenerates other antioxidants in the body, alpha-tocopherol (vitamin E) included
  • Biosynthesis of collagen (component of connective tissue, essential for wound healing), L-carnitine, and certain neurotransmitters
  • Protein metabolism and synthesis of amino acids and hormones
  • Immune function
  • Enhances absorption of nonheme iron (the form of iron present in plant foods)

Vitamin C, through its antioxidant activity, helps reduce the harmful effect of free radicals. Free radicals are molecules that contain one or more unpaired electrons, thus making them very unstable, short-lived and highly reactive species3. Free radicals are naturally formed from activities such as exercise or the conversion of food into energy. There are also diverse environmental sources of free radicals, such as pollution, sunlight or cigarette smoke4

At lower concentrations, free radicals influence many physiological processes in the cell, acting as “second messengers”. However, at excessive concentrations, these reactive oxygen species go beyond cell capacity, ultimately leading to oxidative stress, the cause of oxidation and damage in cells, tissues and organs in the body. This damage may lead to changes in cellular metabolism and even genetic mutations3.  

Oxidative stress is thought to play a key role in a variety of human pathologies including cancer, cardiovascular diseases, diabetes, Alzheimer’s disease, Parkinson’s disease, asthma, hypertension, atherosclerosis, arthritis, and eye diseases such as cataracts and age-related macular degeneration3.

Vitamin C acts as an antioxidant in the body, which means it donates an electron to neutralize free radicals, reducing the harmful effects of these unstable molecules. This action helps counteract oxidative stress and restore balance in the body. Therefore, the antioxidant activity of Vitamin C may contribute to prevent, hinder the development and even help in the treatment of many of the chronic conditions mentioned above, such as cancer, in which oxidative stress plays a crucial and causal role2.

It is important to highlight that much of human physiology is based on this movement of electrons between different molecules, this is called REDOX reactions. The word REDOX is formed from the contraction of the words “reduction” (antioxidants) and “oxidation” (free radicals). Simply put, ‘oxidation’ “steals” electrons and ‘reduction’ gives back or provides electrons. In this case, Vitamin C is an electron donor and reducing agent, acting as antioxidant.

Symptoms of Vitamin C deficiency2

  • Swollen and bleeding gums
  • Soreness and stiffness of the joints and lower extremities
  • Bleeding under the skin and in deep tissues
  • Slow wound healing
  • Anemia
  • Acute vitamin C deficiency leads to scurvy (characterized by fatigue or lassitude, widespread connective tissue weakness, and capillary fragility) 

Cancer treatment

Some of the evidence-based, broad, anti-cancer effects of vitamin C include5:

  • Cytotoxic (direct cancer killing)
  • Anti-proliferative (anti-growth)
  • Anti-inflammatory
  • Antioxidant
  • Pro-oxidant (potent pro-oxidant in cancer cells)
  • Immunomodulator (modulate immune system)
  • Anti-lymphangiogenic (formation of lymphatic vessels)
  • Anti-metastatic (metastasis is the spread of cancer cells from the place in the body where they first formed to other parts of the body)
  • Alters genetic expression (epigenetics)
  • Anti-viral
  • Preservation of mitochondrial potential

Intravenous Vitamin C

In order to achieve these anti-cancer effects, at An Oasis of Healing we give our patients intravenous Vitamin C, the only effective Vitamin C delivery method for healing  cancer and other significant illnesses. The 350–450 mg/dl is the optimal therapeutic plasma vitamin C target window; these plasma concentrations can only be achieved by the intravenous route6.

The necessary dose required to reach this target window and the intended Vitamin C effect is dependent on several factors, among them5:

  • body weight
  • initial vitamin C deficiencies
  • level of inflammation
  • tumor burden

Therefore, it is impossible to recommend a specific dose of Vitamin C, especially when considering cancer treatment, and because no therapy has a one-size-fits-all answer. The dose matters, but many other factors also matter, the duration being one key aspect to achieve the desired “cancer killing” effect. 

Hence, the “right” dose will be dependent on the individual and its unique characteristics. There are many variables arising from individual differences that will affect the effects of intravenous vitamin C, influencing the dosage and ability to reach the therapeutic window. These variables include5

  • The health of the individual
  • The presence and extent of disease
  • The status of vitamin C levels in the body before treatment
  • Smoking status
  • Amount of cancer in the body (called tumor burden)
  • Level of inflammation
  • Microenvironments 

Citing a previous article on our blog, “The right dose is the dose that maximizes the direct and indirect cancer-killing effects, the dose that blocks the inflammation of autoimmune disease or the out of control inflammatory response of the cytokine burst found in COVID19 pneumonia, sepsis, and septic shock, or the dose that aids detoxification…The right dose is simply the dose that provides the appropriate plasma vitamin C levels to achieve the desired effect5”. 

The full article on Vitamin C Dosing for Treating Cancer can be found on our blog.

Oral Vitamin C

Oral vitamin C NEVER achieves the therapeutic window of 350—450 mg/dl or 20–30 mM of plasma ascorbic acid; it can provide a short-lived spike through stomach absorption, but the level always falls short of the minimum required to kill cancer cells. Oral doses typically only reach plasma levels of 70-80 µM, compared to the > 20,000 µM (20 mM) achieved through the intravenous vitamin C delivery. Oral Vitamin C, although useful to supplement a primary intravenous vitamin C treatment program, is by itself inadequate5.  And should not be used to attempt to achieve these higher levels.

Several factors contribute to this inadequacy5

  • Pharmacokinetics (how the body interacts with administered substances for the entire duration of exposure, namely absorption, distribution, metabolism, and excretion7
  • Reduced bioavailability of oral vitamin C 
  • Down regulation of the vitamin C transporters in the gut lining (with higher oral doses)

Even the new liposomal vitamin C products available on the market, that increase bioavailability, reaching maximum levels of 500 µM (compared to 70-80 µM mentioned above), but more reliably 200 µM, are better, but still way below the desired minimum of 1000 µM. And even further away from the +20,000 µM (20 mM) optimal target range threshold5.

As a whole an individual therapy for cancer, vitamin C is inadequate. However, not all is lost with oral vitamin C. Adding oral vitamin C to an intravenous program can help provide an early increase in plasma vitamin C before the intravenous therapy begins5.

Dietary Vitamin C also plays a huge role in disease prevention and overall health and healing. Therefore, oral supplementation and having a diet rich in Vitamin C foods are both great approaches for health maintenance and disease prevention.

Fruits and vegetables are the best sources of Vitamin C. These have the highest content of this vitamin8,9


  • Guava
  • Kiwi
  • Red pepper
  • Green pepper
  • Strawberries
  • Papaya
  • Broccoli
  • Tomato
  • Kale
  • Chili pepper
  • Cauliflower
  • Brussel sprouts
  • Parsley
  • Acerola
  • Black currant
  • Orange
  • Grapefruit
  • Cantaloupe
  • Cabbage
  • Potato
  • Spinach
  • Green peas

Adding more of these foods to your diet will help improve your Vitamin C levels and overall health. One important fact to consider is that Vitamin C nutritional content of food may be reduced by prolonged storage and by cooking because ascorbic acid is water soluble and is destroyed by heat. Steaming may lessen cooking losses.

This is the typical maximum Vitamin C loss (as compared to raw food) 10

Freeze Dry Cook Cook+Drain Reheat 

30% 80% 50% 75% 50%

We always recommend eating most of your fruits and vegetables raw, but this is especially important when considering Vitamin C content.


  1. Jacob RA, Sotoudeh G. Vitamin C function and status in chronic disease. Nutr Clin Care. 2002 Mar-Apr;5(2):66-74. doi: 10.1046/j.1523-5408.2002.00005.x. PMID: 12134712.
  2. National Institutes of Health. Office of Dietary Supplements. Vitamin C Fact Sheet for Health Professionals. Updated Mar 26, 2021., accessed 15 Apr 2022.
  3. Sadiq IZ. Free radicals and oxidative stress: signaling mechanisms, redox basis for human diseases, and cell cycle regulation. Curr Mol Med. 2021 Dec 22. doi: 10.2174/1566524022666211222161637. Epub ahead of print. PMID: 34951363.
  4. National Center for Complementary and Integrative Health. Antioxidants: In Depth. Last Updated: Nov 2013., accessed 15 Apr 2022.
  5. An Oasis of Healing. Health Articles. Vitamin C Dosing for Treating Cancer. Jul 20, 2021., accessed 15 Apr 2022.
  6. Padayatty SJ, Sun H, Wang Y, et al. Vitamin C Pharmacokinetics: Implications for Oral and Intravenous Use. Ann Intern Med. 2004;140:533–537. doi:
  7. Grogan S, Preuss CV. Pharmacokinetics. 2021 Aug 30. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 32491676. 
  8. Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington, DC: National Academy Press, 2000.
  9. U.S. Department of Agriculture, Agricultural Research Service. FoodData Centralexternal link disclaimer, 2019
  10. (dataset) Nutrient Data Lab (2017). USDA Table of Nutrient Retention Factors, Release 6. 2007. USDA Agricultural Research Service., accessed Apr 18, 2022.