It is not often that one thinks about how the food we eat (or don't eat) can impact the development
of cancer in our body. Exposure to carcinogens found in the environment or food as well as radiation
and some infections are known causes of Cancer. Yet, what we intake as nutrients also have roles to
play in prevention, or promotion, of cancer.
In addition to the traditionally known functions played by vitamin, such as assisting synthesis of
DNA and RNA, metabolism of macronutrients, synthesis of blood cells, and strengthening bones,
some vitamins are also antioxidants and may contribute to preventing oxidative damage to genetic
material by salvaging reactive oxygen species. Diets replete with fruits and vegetables have
consistently been shown to be associated with reduced risk of cancer.
On the other hand, the excessive intake of vitamins is also linked to increased risk of cancer, and
hence unsupervised supplementation that may lead to vitamin overdose is not advised. There is a
rise in the consumption of multivitamins, with the belief that these can assist in reducing the risk
of chronic diseases, including cancer.
Cancer
Cancer is a mass of cells that arises from the uncontrolled proliferation of cells, without differentiating
in different lineages. Initiating as benign tumors, these abnormal cells undergo further modifications
that allow them to metastasize, as malignant cells and indicate the development of cancer. Inhibition
of cancer is possible at three stages, preventing the formation of carcinogens, preventing these from
reaching their target sites, and inhibition of cancer after it has initiated. Some of the mechanisms by
which this can be achieved are are formed during tumour promotion and, inhibition of the stages in
arachidonic acid metabolism cascade for prevention of tumor progression. Thus, the identification of
the compound present in foods that can inhibit carcinogenesis after exposure to a cancer causing
agent is very important.
Anticancer properties of Vitamins
Some of the vitamins that have been studied for their link with cancer are as follows:
1. Vitamin A
Vitamin A and its derivatives carry out a large range of functions, including, influencing embryonic
development, as well as cellular growth, differentiation and apoptosis. An inverse relationship has
been foun between intake of vitamin A and cancer development Green and yellow vegetables that
contain carotene, the precursor of vitamin A, as well as foods like whole milk and liver contain
vitamin A. Increased intake of this vitamin protects against the action of UV light-induced carcinogenesis.
Retinoids exert anticancer properties through their anti-proliferative, pro-apoptotic and antioxidant effects.
They are observed to reverse human epithelial lesions, while inducing the differentiation of myeloid
cells, as well as prevent cancers of the lung, liver and breast. Retinoids are also considered effective
for prevention of head and neck cancers. Precancerous lesions such as leukoplakia, actinic keratosis
and cervical dysplasia can be treated with retinoids.
These compounds also delay the development of skin cancer in those individuals who suffer from
xeroderma pigmentosum, wherein, the person is at increased risk for UV-induced cancer. Many
types of retinoids, by themselves or in conjunction with interferons and esterogen antagonist are
shown to treat breast cancer and can even prevent it. This is especially so during the initial stages
of cancer progression, but the effect begins to reduce as the cancer becomes more aggressive.
2. Vitamin C
Frequent consumption of vitamin C is associated with reduced risk of esophageal and stomach cancers.
As per recent studies, vitamin C enters the cancer cells almost immediately after it is exposed and acts
as a cytotoxic agent. Oxidation of vitamin C produces substances that have antitumor activity through
the production of molecular species such as hydrogen peroxide and some aldehydes, as well as promotes
lipid peroxidation whose secondary products have inhibitory action on malignant cell proliferation.
Vitamin C also promotes collagen synthesis which strengthens the natural barrier for preventing infiltration
and metastatic spread of the cancer. Inhibition of tumor growth by vitamin C is also achieved through
enhancement of immune system against cancer by vitamin C.
3. Vitamin K
A fat-soluble vitamin, this molecule has inhibitory effect on cancer cells through oxidative stress in
several cell lines. Vitamin K2 has been shown to have anti-cancer properties against many cancer
cell lines, including those of liver, lungs, colorectum, stomach and breast. In fact, dietary levels of
vitamin K are associated inversely with advanced prostate cancer.
Vitamin K2 has also been reported to have inhibitory activity on hepatocellular carcinoma cell lines
by suppressing cellular division. It also has the ability to induce apoptosis in certain cancer cells, an
ability that is associated with the p53 status in these cells.
Cell death is observed to be induced in cancer cells by vitamin K3 in combination with vitamin C through
oxidative stress, lipid peroxidation, calcium regulation and modification of ATP levels. This has been
extensively studied in bladder cancer cell lines.
4. Vitamin D
Vitamin D includes vitamins D2 (ergocalciferol) and D3 (cholecalciferol), and is a known anticancer
micronutrient which acts through the regulation of different genes by vitamin D receptor. The mode
of action of this vitamin against cancer ranges from inhibition of cell cycle progression and tumor
growth by preventing cellular proliferation to induction of apoptosis and acting on cellular adhesion
molecules and growth factors that are involved in tumorigenesis.
The development of vasculature to provide nutritional support to the rapidly dividing cells is one of
the hallmarks of a progressing cancer. Vitamin D3 is known to inhibit angiogenesis in several cancer
cell lines. Vitamin D also promotes antioxidant activity, as oxidative damage to cellular genetic material
is also commonly seen in cancer cells and promotes development of mutations that give the cancer
cells a selective advantage over others.
Autophagy is a process which allows a cell to survive in stress conditions like oxygen and nutrient
deprivation. It is important for preventing progression of tumors in vivo and is regulated by vitamin
D. When cancers in the early stages are treated with vitamin D, cellular transformation induces
autophagy, as a result of which the damaged chromosome! and organelle debris are cleared. Later,
proteins like p53 initiate cellular repair processes if the cell is still in the initial phases of cancer
development, or otherwise, trigger cellular death.
Vitamin E
A major fat-soluble vitamin, vitamin E may prevent cancer by decreasing the formation of mutagens
that arise due to oxidation of lipids, as well as reducing the oxidative stress in the epithelial cells.
This antioxidant vitamin also modulates apoptosis, cell cycle and transcriptional events.
Over-intake of vitamins also linked to cancer?
There have been studies that implicate high doses of certain vitamins in association with cancer,
especially when toxicity occurs in the presence of other risk factors for cancer. For instance, as per
some studies, high doses of vitamin C in the presence of arsenic trioxide has been linked to serious
side effects and disease progression in Acute Myeloid Leukemia, refractory metastatic colon cancer,
as well as metastatic melanoma. Further, high dosage of vitamin C taken along with some chemotherapeutic
drugs can also increase the toxicity. Yet other studies have shown that the use of multivitamins is
over-hyped and that it confers no known benefit with respect to preventing chronic disorders in healthy
individuals. Also, the World Cancer Research Fund and the American Institute for Cancer Research
have ruled against using dietary supplements for preventing cancer.
Certain studies have indicated that while the consumption of multivitamins is associated with
decreased risk of some cancers like those of the colon and bladder, it may also lead to higher
chances of Non-Hodgkin's lymphoma. Thus, in long term, use of multivitamins may slightly increase
the risk of cancer but do not cause any major harm on short term.
The possible effects, beneficial or harmful, of vitamins with respect to cancer are still under investigation.
However, other benefits of vitamins are well known, as their deficiencies are linked with serious
consequences. Further, the possible harms also arise due to over-intake of these micronutrients. Hence,
within the dietary recommended values, the intake of vitamins is beneficial for overall health. The best
way is to consume them from naturally grown fruits and vegetables rather than resorting to supplements
unless a doctor has prescribed them. Within limits, vitamins will play wonders for your health!
