Vitamin C in vitro (in test-tube) shows toxic effects against certain kinds of cancer cells, but not for healthy cells1,2,3. It stems from a bit different, more voracious metabolism of a malignant cell and is called selective cytotoxicity. A few well-known mechanisms are engaged in a potentially anticancer effect of vitamin C, including the influence on collagen synthesis, antioxidant effect, the creation of new blood vessels that feed the tumor and even gene transcription1,2,3. There are also a few studies on animal models, which indicate the effectiveness of large doses of vitamin C in inhibiting the growth and metastases of cancer1,2,3. However, we should be interested primarily in the research on humans – the way from proved effectiveness in test-tubes or tests on rodents to evidence of clinical effectiveness is very, very long. There are three cases of people described in literature, who were cured of cancer by means of vitamin C, but there are serious doubts concerning the effects, among others, applying simultaneous treatment (including surgical) or the possibility of idiopathic remission in the case of kidney cancer4.
Vitamin C for cancer - overview
It is important that when administered orally, relatively low concentration of vitamin C in blood can be obtained in comparison to intravenous infusions. The same dosage administered in the infusion gives around 25 times larger vitamin C concentration in blood than the one administered orally2. Therefore, it should be assumed that oral supplementation makes no sense.
Vitamin C was also used next to the standard treatment and there are certain studies, which are in progress or at the stage of recruitment of subjects1. Preliminary results prove that vitamin C infusions ALONG WITH THE STANDARD THERAPY provide good result. This is not always a bigger chance for curing the diseases, but it rather means increased well-being and better functioning of the patient1,2,3, which already is a great benefit. Although vitamin C seems to support radiotherapy and chemotherapy, it is not always the case in the second therapy type1,2, where sometimes it may even impair its effectiveness. Therefore, patients should not undertake vitamin C therapy without consulting their doctors.
Does vitamin C cure cancer?
Vitamin C on its own, even in the form of intravenous infusions probably does not cure cancer and should not be recommended in such a form. Does vitamin C in large doses may support conventional cancer treatments? Possibly yes – we are not sure, but known mechanisms of operation and preliminary research results indicate that it has the potential. A more precise answer will be known in subsequent years, when the results of the clinical research in progress are published.
A separate question is whether it is worth to apply vitamin C in cancer prevention. In fact, epidemiological research indicate that higher intake of vegetables and fruits (main source of vitamin C) is connected to lower cancer rate5. However, there are many disturbing factors related to the fact, for example, that fruit and vegetables are also rich in a range of other phytochemicals and fiber. We should rather think that these components, along with vitamin C naturally occurring in products protect us from cancer and not vitamin C itself works like this. Especially that vitamin C concentration in blood under the influence of fruit, vegetables or supplements intake is relatively small and it seems impossible that it could influence cancer.
It should also be borne in mind that vitamin C, in spite of its relative safety of use, may cause side effects. Vitamin C is metabolized to oxalic acid, which may be stored in kidneys in the form of kidney stones. This effect is confirmed in many studies7. Men are more endangered than women and the people with kidney stones history in the family should be especially careful. Also among people with certain genetic diseases, vitamin C supplementation may be dangerous1,2,3. Depending on the organisms’ iron nutrition, it may beneficial or unbeneficial. There are also justified concerns regarding higher risk of clots when applying intravenously high doses of vitamin C7.
Summing all of this up, vitamin C at it own, especially when administered orally is not able to cure cancer or at least there is no evidence to prove this. At the same time, vitamin C in the form of intravenous infusions, administered simultaneously with a conventional treatment may increase its effectiveness or/and the patient’s well-being. This issue requires further research, which is intensively being carried out. Applying vitamin C supplementation in cancer prevention is probably pointless. Eating vegetables and fruit rich in vitamin C may protect from cancer, but this is because of the whole array of phytochemicals and not only vitamin C.
Taking vitamin C is therefore classified in the stream of complementary medicine, which still is alternative medicine, but applied along with the conventional treatment – and not instead of it. Certainly, most of complementary therapies is completely worthless (as homeopathy). However, certain methods may be helpful and especially in the cases with very bad prognosis no wonder that people want to take advantage of them.
I also recommend to take a look at the information on vitamin C gathered at the website of National Cancer Institute.