The concept that
cancer can be prevented through vitamin supplementation stems
from early observations correlating human disease with vitamin
deficiency, such as pernicious anemia with vitamin B12
deficiency, and scurvy with Vitamin C deficiency. This has
largely not been proven to be the case with cancer, and vitamin
supplementation is largely not proving effective in preventing
cancer. The cancer-fighting components of food are also proving
to be more numerous and varied than previously understood, so
patients are increasingly being advised to consume fresh,
unprocessed fruits and vegetables for maximal health benefits.
The Canadian Cancer Society has advised Canadians that the
intake of vitamin D has shown a reduction of cancers by close to
60%, and at least one study has shown a specific benefit for
this vitamin in preventing colon cancer.
Vitamin D and its protective effect against cancer has been
contrasted with the risk of malignancy from sun exposure. Since
exposure to the sun enhances natural human production of vitamin
D, some cancer researchers have argued that the potential
deleterious malignant effects of sun exposure are far outweighed
by the cancer-preventing effects of extra vitamin D synthesis in
sun-exposed skin. In 2002, Dr. William B. Grant claimed that
23,800 premature cancer deaths occur in the US annually due to
insufficient UVB exposure (apparently via vitamin D deficiency).
This is higher than 8,800 deaths occurred from melanoma or
squamous cell carcinoma, so the overall effect of sun exposure
might be beneficial. Another research group estimates that
50,000–63,000 individuals in the United States and 19,000 -
25,000 in the UK die prematurely from cancer annually due to
insufficient vitamin D.
The case of beta-carotene provides an example of the importance
of randomized clinical trials. Epidemiologists studying both
diet and serum levels observed that high levels of
beta-carotene, a precursor to vitamin A, were associated with a
protective effect, reducing the risk of cancer. This effect was
particularly strong in lung cancer. This hypothesis led to a
series of large randomized clinical trials conducted in both
Finland and the United States (CARET study) during the 1980s and
1990s. This study provided about 80,000 smokers or former
smokers with daily supplements of beta-carotene or placebos.
Contrary to expectation, these tests found no benefit of
beta-carotene supplementation in reducing lung cancer incidence
and mortality. In fact, the risk of lung cancer was slightly,
but not significantly, increased by beta-carotene, leading to an
early termination of the study.
Results reported in the Journal of the American Medical
Association (JAMA) in 2007 indicate that folic acid
supplementation is not effective in preventing colon cancer, and
folate consumers may be more likely to form colon polyps.
Prevention Chemoprevention >>
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Cancer
Classification
1. Nomenclature
2. Adult cancers
3. Childhood cancers
Signs and symptoms
Diagnosis
1. Investigation
2. Biopsy
Treatment
1. Surgery
2. Radiation therapy
3. Chemotherapy
4. Targeted therapies
5. Immunotherapy
6. Hormonal therapy
7. Symptom control
8. Complementary and alternative
9. Treatment trials
Prognosis
1. Emotional impact
Causes
1. Chemical carcinogens
2. Ionizing radiation &
Infectious diseases
3. Hormonal imbalances
& Immune system dysfunction
4. Heredity & Other causes
Pathophysiology
1. Epigenetics
2. Oncogenes
3. Tumor suppressor genes
4. Cancer cell biology
4.1 Clonal evolution
4.2 Biological properties of cancer cells
Prevention
1. Modifiable ("lifestyle") risk factors
2. Diet
3. Vitamins
4. Chemoprevention
5. Genetic testing
6. Vaccination
7. Screening
Epidemiology
History
Research |
