Vitamin C, a natural substance found in many foods and dietary supplements, has long been known to carry several important health benefits. Most notable among these benefits is its critical role in the formation and health maintenance of collagen.  Therefore, Vitamin C is important for the health of skin and connective tissues throughout the body.
Intravenous Vitamin C has, in fact, been used for aesthetic purposes such as skin rejuvenation and skin whitening.  Vitamin C also is important for the health of bone, cartilage, and teeth, and also plays a very important role in iron absorption; thus impacting overall body health in the many critical ways iron does.
Probably the most controversial, yet exceedingly exciting, a benefit of Vitamin C is its suggested role in fighting cancer. The basis of attributing to Vitamin C this cancer-fighting ability is predicated on two main observations: Vitamin C’s property as an antioxidant and its property as a factor that helps enhance the function of the immune system. Several studies have documented the fact that Vitamin C acts as a natural antioxidant.
This property has been shown in laboratory studies to result in Vitamin C being an effective anti-cancer agent when high concentrations are reached in cells. [3,4] This Vitamin C-induced anti-cancer activity is mediated through the production of hydrogen peroxide (H2O2). H2O2 is an oxygen radical that induces apoptosis (programmed cell death) in cancer cells thus resulting in their elimination. [5,6] It is thought that this effect results from the H2O2 damaging the cells’ DNA; cells that do not immediately undergo apoptosis are damaged and rendered more vulnerable to the anti-cancer effects of chemotherapy and radiation.
The significant role that Vitamin C plays in the proper functioning of the immune system is now well documented.  Not only is Vitamin C present in high concentrations in immune cells, such as T cells, it has also been shown to be necessary for these cells’ proper functioning.  Vitamin C is also known to be consumed in the body at much higher rates in the presence of infection. The immune system, while commonly and automatically associated with guarding against and fighting infections plays critical roles in health maintenance that span far beyond those confines.
Immune system functioning works not only to prevent and fight infections, help the body’s tissues heal after injury, but also works to combat cancer. The immune system’s role in fighting cancer is a versatile and multifaceted one, involved in not only fighting cancer but also preventing it from taking hold in the first place.  The important role that Vitamin C plays in supporting immune function, therefore, highlights the important function of Vitamin C as an anti-cancer agent.
Oral vs. Intravenous Vitamin C
Since Vitamin C cannot be synthesized by the body, it needs to be taken in from outside sources. This is an interesting peculiarity of human physiology since Vitamin C can be synthesized by most animals and plants from the more basic compounds of D-Glucose and D-Galactose.  Typically, Vitamin C is taken in orally through ingestion of various foods and dietary supplements. Intravenous administration is another method to take in this compound and has been used and studied as a way to reach a higher concentration of Vitamin C in the bloodstream, in order to achieve better therapeutic effects. 
This turns out to be a consideration of practical significance as studies have shown that oral Vitamin C does not improve survival in cancer [11,12]. Intravenous administration is required in order to achieve the high enough blood concentrations required for the anti-cancer effect of Vitamin C,  This is, in large part, due to the variability in the reliability of oral absorption of Vitamin C which results in lower blood concentrations, in general, compared to intravenous administration. [14,15]
The Half-life of Vitamin C in the body is also relatively short (about 2 hours), hence making it difficult for a high enough concentration to be reached at any point in time when the dependence is on gradual absorption through the oral route. As a result of all of these observations, it is now accepted that any significant benefit from Vitamin C in fighting cancer would have to be delivered in the form of high dose intravenous administration of the compound.
Evidence for treatment of cancer
Laboratory studies have shown that Vitamin C is directly toxic to cancer cells as long as certain concentration levels are achieved. [16,17] Animal studies have demonstrated the anti-cancer effects of Vitamin C for cancers of the pancreas, liver, colon, prostate, ovary in addition to mesotheliomas and neuroblastomas.
Until recently, human trials have shown little consistency in confirming the conclusion reached, based on laboratory and animal data, that Vitamin C can help in treating cancer. Early data from a University of Iowa trial on Glioblastoma Multiforme (an aggressive form of brain cancer that is the most common among adults) has recently become available. The results showed that when conventional treatment with chemotherapy and radiation was combined with high dose intravenous Vitamin C, the survival time was increased by 4-6 months compared to conventional treatment without Vitamin C.
In addition to its own anti-cancer properties, Vitamin C has also been shown to increase the effectiveness of certain chemotherapy agents in fighting cancer. Examples include Cisplatin, Dacarbazine, Doxorubicin, and Paclitaxel, in addition to the anti-estrogen agent used in treating breast cancer, Tamoxifen. [18-21] Another beneficial effect of Vitamin C is its ability to reduce the toxicity and side effects associated with chemotherapy. Intravenous high dose Vitamin C has, in fact, been shown to improve quality of life and lessen the side effects of chemotherapy and radiation in breast cancer patients. 
In conclusion, high dose Vitamin C therapy remains controversial and not uniformly accepted as a reliable cancer treatment within the mainstream medical dogma.
Despite this, however, a positive view of this therapy combined with increasing evidence for its effectiveness is gathering momentum. There is the agreement that high dose Vitamin C therapy is overall a very safe treatment in cancer patients.
While concerns over interaction with chemotherapy are frequently expressed, studies have in fact shown that it is not only safe with most chemotherapeutic agents but that it also may improve the effectiveness and reduce the side effects of chemotherapy.
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