Cancer and Vitamin C What are the facts?
By Dr Julian Kenyon

The use of vitamin C in cancer is highly controversial. There is evidence that vitamin C is preferentially toxic to cancer cells starting with research published in 1969 and several papers since.

The theory behind the toxicity of vitamin C is due to the relative deficiency of catalase in tumour cells. Catalase is an important enzyme present in every cell in the body. Catalase in cancer cells occurs at ten to a hundred times less concentration than in normal cells.

Looking at the specific metabolism of cancer cells and targeting the vulnerable aspects of cancer cell metabolism is becoming increasingly popular and has been the subject of several papers. For example inhibiting the protease and collagenase enzymes produced by cancer cells can be very helpful and a number of constituents in fermented soya products can do this. These particular enzymes are produced by cancer cells in order to dissolve surrounding tissue so the cancers can increase in size and travel around the body in order to form secondary growths.

Some studies have shown that people with high circulating volumes of vitamin C have lower cancer incidence. This is noted epidemiologically in populations who eat large amounts of fruit, the best example are the Costa Ricans. However, it is not at all sure that the situation is the same when you have got cancer as to when you haven't got cancer. Our work is indicating to us, in some cases, that the use of antioxidants such as vitamin C and indeed vitamin A and vitamin E might not be helpful if you actually have cancer, because the cancer cells may use these antioxidants as protection for themselves and may make the patient worse. A study published in the New England Journal of Medicine in 1994, looked at the effects of carotenes (vitamin A preparations), to see whether they would be helpful in preventing cancer, the study yielded unexpected results. Two major intervention studies were carried out with beta carotene, one in Finland among smokers and the other in the United States among people who had been exposed to asbestos. Smokers have a higher incidence of lung cancer than non-smokers, people exposed to asbestos have a higher incidence of mesothelioma of the pleura, which is a cancer of the covering membrane of the lungs, than people who have not been exposed. More people receiving the supposedly protective supplements died from cancers of the lung, pleura and other cancers, than people receiving a non-active medication (a placebo). It was considered at the time that these studies had faulty design. I have looked at them in detail and I do not think that is the case. I think the probability is that amongst the people on the trial who had been exposed to asbestos and who were smokers, there would have been a significant number with very very small cancers, either lung cancers or mesothelioma of the pleura which were asymptomatic. The use of antioxidant vitamins (in this case beta carotene, which is essentially a vitamin A derivative), 'fed' the cancer and produced the higher death rate amongst the study group. The number of patients dying in this study wasn't high, but it was a significant number. I am unable to see any design flaws in these studies.

So, how does this apply to vitamin C and vitamin E in cancer? The studies are all very confused on this issue, but my feeling is that the use of any antioxidant vitamins when a patient has got cancer, means that the cancer cells may use those antioxidant vitamins in order to feed the cancer. This is by no means proven, and I am well aware that this a controversial statement, but I think it is an important question to ask.

What about using vitamin C as a pro-oxidant instead of an antioxidant? In this situation one would have to use very high doses of vitamin C. It is not possible to use vitamin C as a pro-oxidant when taking it by mouth, as the maximum concentration in the serum which one can achieve by oral supplementation is 5 mg per 100 cc's. In order to achieve pro-oxidant levels, one needs to have serum levels of at least 50 mg per 100 cc's. This has to be achieved by giving the vitamin C intravenously. The effect of the use of vitamin C as a pro-oxidant is to oxidise the cancer cells, and that is the same mechanism as many chemotherapy drugs use. The advantage that high dose intravenous vitamin C has is that it does not carry the down sides of chemotherapy. There are several papers, including one in the British Journal of Cancer showing that vitamin C used at pro-oxidant levels is effective in killing cancer cells, so it is possible to use high dose intravenous vitamin C as a chemo-therapeutic agent. We use this approach regularly in our clinic, and we measure serum levels of vitamin C following courses of vitamin C used at these levels. Generally speaking the more tumour load there is, the more courses of high dose intravenous vitamin C we have to use. The standard is for us to use a three week course of high dose intravenous vitamin C. This is one of our most successful approaches to the treatment of cancer.

Several studies are being carried out in the United States, to look further at the use of intravenous vitamin C as a cancer killing agent.

So where does that leave the man in the street? If you have not got cancer then the use of anti-oxidants is a good idea.

If you have got cancer, then this is a completely different ball game, and you may have to think carefully and get informed advice on this. Unfortunately informed advice assumes that it is a good thing to take anti-oxidants if you have got cancer. I would suggest that this may not always be the case.