The role of vitamin C (ascorbate) in cancer has been debated for decades. Study shows that vitamin C at high concentrations is toxic to cancer cells in vitro though several old studies suggest inconsistent or inconclusive clinical benefit. So what do the latest studies say?
Cancer compromised vitamin C status.
Cancer patients have compromised vitamin C status, This is supported by dozens of studies consistently showing that patients with cancer have lower mean plasma vitamin C status than healthy controls. The reason is likely due to enhanced metabolic turnover as a result of oxidative and inflammatory aspects of the disease process.
There is also evidence that administration of some anticancer therapies, such as cisplatin, fluorouracil, nilotinib, and interleukin-2, can significantly lower the vitamin C status of oncology patients and result in scurvy-like symptoms in some cases.
Vitamin C can kill cancer cell
Early studies on ascorbate and its derivatives support that high extracellular concentration (greater than 1000 µmol/L) of Vitamin C is toxic to cancer cells.
It was found that in the presence of metals, vitamin C produces hydrogen peroxide, a powerful oxidant that can kill cancer cells. It can also act on DNA and affect stem cell development.
Oral Vitamin C is insufficient source to achieve the cytotoxic effect.
Studies found out that the uptake of ascorbate from the intestinal tract is very tightly controlled. Even after multiple consumption of fruits and vegetables daily, and maximum oral administration, peak plasma concentration rarely exceeds 200 μmol/L! Remember that the concentration must be greater than 1000 µmol/L to be toxic to cancer?
Only intravenous administration of vitamin C produces high plasma and urine concentrations that might have antitumor activity. This is because it bypassed the regulation happening in the intestinal tract, resulting in significantly higher plasma concentrations
Vitamin C is an Antioxidant but also a Pro-oxidant
Clinical studies show that the administration of antioxidants during cancer therapy causes a decrease in the level of markers of oxidative stress in blood serum that can be counterproductive in the fight with cancer, if not regulated.
Vitamin C is a potent antioxidant preventing oxidative damage to lipids and other macromolecules. It does not adversely interfere with chemotherapy and can also exhibit bimodal activity as a pro-oxidant at a higher concentration.
In the case of Vitamin C, many studies indicate the toxicity of ascorbate to cancer cells is due to its pro-oxidative activity, which induces the formation of hydrogen peroxide (H2O2) and oxidative stress. This leads to oxidative stress-induced autophagy of cancer cells.
Helps in Cancer Treatment
Pre-clinical studies indicate that vitamin C may in fact act synergistically in combination with different chemotherapeutic agents.
Combination of cisplatin treatment with vitamin C enhances the therapeutic effect of cisplatin, and has a strong antiproliferative effect in cervical cancer cells. It makes these cells more susceptible to apoptosis or cell death. Thus, the suggestion of combining vitamin C therapy with another cancer drug may enhance its effects.
Vitamin C has also been recognized for protection against radiation-induced cell damage.It is a safe supportive intervention to decrease inflammation in the patient and to improve symptoms related to antioxidant deficiency, disease processes, and side effects of standard cancer treatments.
In summary, the potential for vitamin C anti-cancer properties has been fortified by a series of studies conducted. The controversy around vitamin C use in cancer therapy has risen from early misunderstandings around the pharmacokinetics of oral and intravenous use.
Vitamin C has been found to support chemo/radiotherapy, improving treatment effects and patients’ quality of life by reducing adverse side effects. Given its lack of toxicity, ready availability and low cost, new information on its mechanism(s) of action and further use in cancer will be a breakthrough in clinical practice. With a number of early phase clinical trials currently underway, hopefully it will result in sound clinical data that will avert further dispute regarding its usefulness.
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