CANCER AND VITAMIN C: OXIDANT OR ANTIOXIDANT?

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CANCER AND VITAMIN C: OXIDANT OR ANTIOXIDANT?

(Editor's note: Many DY Newsletter readers have been sending me their

questions about apparently conflicting reports on vitamin C and cancer.

Does vitamin C always help? Does it ever harm? I asked vitamin C expert

Dr. Hickey to please provide a better response than I possibly

could, and he has most certainly done so.)

THE ANTIOXIDANT PARADOX

by Steve Hickey, PhD

Department of Biological Sciences, Metropolitan University of Manchester

Dr. Horrobin was an excellent pharmacologist. He identified that

the action of antioxidants can be paradoxical, in that they can both

promote and inhibit cancer growth. However, the mechanism he described

(1) is probably incorrect. In almost all circumstances, except a

fast-growing malignancy, antioxidants will be helpful. In the case of

malignancy, some antioxidants will be very beneficial, although a level

of sophistication is required in their selection.

One - Healthy and precancerous cells

The processes and signals that increase cellular proliferation make

cells more oxidising. Antioxidants inhibit this proliferation; hence,

damaged cells take longer to develop into a cancerous state when

antioxidants are present.

Two - Rapidly growing cancer

Antioxidants may have a paradoxical effect on fast-growing cancer cells.

Malignant cells can increase their internal oxidative state to a high

level, which promotes growth. However, a proportion of such cells will

be driven towards even higher levels of oxidation. At these extreme

levels, cells usually commit suicide (apoptosis), rather than becoming

cancerous. The process of cell suicide relies on oxidative stress and

redox signalling. As the oxidation level becomes sufficiently high, the

cell takes this increase as a signal to kill itself.

Antioxidants can reduce the oxidative stress and relieve the apoptotic

pressure on such cancers. Thus, while antioxidants may lower the rate of

cell division in healthy cells, they can promote growth of malignant

cancer cells, by stopping these abnormal cells from dying.

(DY Editor's comment: Interestingly, the Gerson Therapy, which is

extremely high in antioxidants from huge quantities of raw vegetable

juices, is particularly effective against one of the fastest-rowing of

all cancers, malignant melanoma, skin cancer.)

Three - Kill cancer cells and help normal cells

At very high levels, some antioxidants, such as vitamin C or lipoic

acid, will kill cancer cells. Paradoxically, this is because they act as

oxidants, or free radical generators, in the highly oxidised environment

of cancer cells. In healthy cells, vitamin C and lipoic acid continue to

act as antioxidants. The possibility that vitamin C produces free

radical damage has been suggested as a possible side effect of high

doses. As we learn more about the process, it becomes clear that the

free radicals are only produced in cancer cells. Healthy cells get an

antioxidant boost, whereas cancer cells are damaged by this

" side-effect " .

Four - Don't feed the cancer

Cancer cells are sick and require specific nutrients, in particular,

glucose. Cancer cells use less oxygen than healthy cells, and their

metabolism tends towards being anaerobic. This form of metabolism relies

heavily on the availability of sugar. The " wrong " nutrients, eg. sugars

and starches, feed the cancer and promote its growth.

Cancer cells absorb glucose using biochemical pumps. These same pumps

also absorb vitamin C, as dehydroascorbate, the reduced form of vitamin

C, which is chemically similar to glucose. If more glucose is present,

then less vitamin C is absorbed by the cells.

However, cancer cells that are deprived of glucose absorb higher levels

of vitamin C, which produces oxidising free radicals, pushing the cancer

cells towards death. For some time, Dr Ely has reported that the

beneficial effects of vitamin C can be increased by reducing sugar

intake. (2,3)

Five - A targeted approach

Prevention of cancer requires a broad spread of antioxidants. A normal

diet can provide some antioxidant protection. However, many dietary

antioxidants that are effective against cancer have been isolated, and

are available in supplement form. To avoid cancer and slow its

development, a high intake of antioxidants is necessary, consistent with

the orthomolecular approach to nutrition, pioneered by Linus ing and

others.

Some people will be unfortunate and find they have a rapidly growing and

malignant cancer. With such a malignancy, there are two possible

approaches - lots of dietary antioxidants to prevent growth, or specific

antioxidants to kill the cells. High levels of selected antioxidants,

such as vitamin C and alpha-lipoic acid, will kill malignant cancer

cells or inhibit their growth (by oxidation). People taking this

nutritional form of cytotoxic chemotherapy should not take other

additional antioxidants, as these might work in the opposite direction,

preventing the free radical damage, which is needed to destroy the

cancer cells.

A new description of cancer

In our forthcoming book, Cancer: Nutrition and Survival, (4) we explain

the biology of cancer. This new approach describes free radical

reactions as core mechanisms in the development of the disease. It also

shows that anticancer agents are not rare and do not need to be

poisonous to the patient. Non-toxic antioxidants, found at low levels in

the diet, can kill cancer cells and prevent proliferation. To a

biologist, this finding is expected and is based on solid science. It

seems, once again, that Linus ing was correct in his assertions that

orthomolecular medicine would provide the most productive approach to

cancer research.

Beta-carotene

Horrobin's paper attempts to explain the problem with beta-carotene in

smokers. It appeared that the " antioxidant " beta-carotene could,

paradoxically, increase the risk of cancer. This finding is consistent

with the model described above.

Beta-carotene is unlikely to act as an antioxidant in the lungs of

smokers. Carotenoids' antioxidant properties depend upon an ample supply

of high-energy electrons. For example, vitamin C can supply such

electrons to reduce oxidised carotenoids, returning them to their free

radical quenching function. In the absence of high levels of vitamin C,

as in the oxidising environment of a smoker's lung, carotene radicals

can propagate free radical chain reactions (5)

Thus, we would predict that beta-carotene would act as an OXIDANT in the

lungs of smokers (unless, perhaps, the smokers were taking several grams

of vitamin C every day)! By acting as an oxidant, the beta-carotene is

predicted to increase the risk of cancer.

References:

1. Horrobin D.F. (2001) The paradox of antioxidants and cancer. American

Journal of Clinical Nutrition, Vol. 74, No. 4, 555.

2. Marks P.A. Bishop J.S. (1957) Glucose metabolism in subjects with

neoplastic disease response to insulin and glucose tolerance followup

studies. Proc Am Assoc Canc Res, 2, 228-229.

3. Ely J.T. (1996) Glycemic modulation of tumor tolerance. J Ortho Med,

11(1), 23-34.

4. Hickey S. H. (2005) Cancer: nutrition and survival. (In

press).

5. Halliwell B. Gutteridge J.M. (1998) Free Radicals in Biology and

Medicine,