Re: Antioxidants during cancer therapy

PM wrote:

Antoine Lacroix wrote:
Is it appropriate to have a diet rich in antioxidants when undergoing cancer
treatments like radio and chemotherapy?

Some serious authors recommend a diet rich in berries and green vegetables.
However, some doctors say that the effect of these could lessen the impact
of cancer treatments. What about omega-3 ?

many thanks.

Merely my opinion --- I am aware of no direct evidence that
antioxidants can interfere with the effects of chemotherapy or
radiotherapy, but there are theoretical reasons why they might. I
suggest avoiding large doses during the treatment. I know of no
reason why omega-3 would be a problem.

Peter Moran

http://en.wikipedia.org/wiki/Antioxidant [excerpts]
his article or section is in need of attention from an expert on the subject.
WikiProject Molecular and Cellular Biology or the Molecular and Cellular Biology
Portal may be able to help recruit one.This article contains unencyclopedic lists
that may require cleanup.

An antioxidant is a chemical that reduces the rate of particular oxidation
reactions in a specific context, where oxidation reactions are chemical reactions
that involve the transfer of electrons from a substance to an oxidizing agent,
this generally results in different chemicals to the original ones.

Antioxidants are particularly important in the context of organic chemistry and
biology. All living organisms maintain a reducing environment inside their cells,
all cells contain complex systems of antioxidants to prevent chemical damage to
the cells' components by oxidation. These antioxidants include glutathione and
ascorbic acid and are substrates for enzymes such as peroxidases and
oxidoreductases.

Antioxidants are widely used as ingredients in dietary supplements used for health
purposes such as preventing cancer and heart disease. Studies have suggested
antioxidant supplements has benefits for health, but several large clinical trials
did not demonstrate a definite benefit for the formulations tested, and excess
supplementation may even be harmful.

Dietary supplementation has few specific antioxidants compared to a broad diet
rich in phytonutrients, which will yield thousands of different polyphenol
antioxidants available for metabolism.

Applications in nutrition and medicine

[edit] Health preservation

Antioxidants are chemicals that reduce oxidative damage to cells and biomolecules.
Researchers have found a high correlation between oxidative damage and the
occurrence of disease.[citation needed] For example, low density lipoprotein (LDL)
oxidation is associated with cardiovascular disease. The process leading to
atherogenesis, atherosclerosis, and cardiovascular disease is complex, involving
multiple chemical pathways and networks, but the precursor is LDL oxidation by
free radicals, resulting in inflammation and formation of plaques.

Research suggests that consumption of antioxidant-rich foods reduces damage to
cells and biochemicals from free radicals.[citation needed] This may slow down,
prevent, or even reverse certain diseases that result from cellular damage, and
perhaps even slow down the natural aging process. This is the basis for the
free-radical theory of aging.

Some of the reactions in the body that produce free radicals involve metal ions.
Some antioxidants, such as the tannins in walnuts and tea, chelate (wrap around)
metal ions. This not only reduces the formation of ion-dependent free radicals,
but also prevents the metal ions from oxidizing cells and biochemicals directly.

Some studies suggest that by destroying free radicals and reducing cellular
damage, antioxidants in the diet can have positive health effects, such as
preventing macular degeneration (studied in the Age-Related Eye Disease Study);[8]
maintaining the immune system;[9] potentially preventing neurodegeneration due to
oxidative stress;[10] preventing DNA damage;[11] and lowering the risk of
cardiovascular disease.[12] Any specific antioxidant may perform only a small
fraction of these functions. The mixed results from controlled studies using
antioxidant vitamins suggest that other antioxidant substances in fruit and
vegetables at least partially explain the better health of those who consume more
fruit and vegetables.[13] Dietary antioxidants are not the primary antioxidant
inside the body, and there are still many questions as to how polyphenols and
other dietary antioxidants protect cells and biochemicals from oxidation. Some
antioxidants preserve, or even recycle, other antioxidants such as vitamin E.

[edit] Adverse effects

Relatively strong reducing acids can have anti-nutritional effects by binding to
dietary minerals in the gastrointestinal tract and preventing them from being
absorbed. Notable examples are oxalic acid and phytic acid, which are high in
plant-based diets. Some tannins also have this negative characteristic. Calcium
and iron deficiencies are not uncommon in mideastern diets where there is high
consumption of phytic acid present in beans and unleavened whole grain bread.
These anti-nutrients can result in deceptively high oxygen radical absorbance
capacity (ORAC) ratings given to various "healthy" beverages and foods,
particularly: <see webpage>

Other extremely powerful nonpolar antioxidants such as eugenol also happen to have
toxicity limits that can easily be exceeded with the misuse of essential oils.

While antioxidants supplementation is widely hypothesized to prevent the
development of cancer, antioxidants may, paradoxically, interfere with cancer
treatments.[14] One explanation for this effect is that the growth-promoting
environment of cancer cells leads to high levels of redox stress under baseline
conditions, and this makes cancer cells more susceptible than normal cells to the
further stress of chemotherapy or radiation therapy. So by reducing the redox
stress in cancer cells, antioxidant supplements could decrease the effectiveness
of the therapy designed to kill them.

Clinical trials

Although some levels of antioxidant vitamins and minerals in the diet are required
for good health, there is considerable doubt as to whether antioxidant
supplementation is beneficial, and if so, which and what amount of antioxidant(s)
are optimal.

One study of lung cancer patients found that those given beta-carotene supplements
had worse prognoses. Two 1994 studies found an increased rate of lung cancer in
smokers supplementing with beta carotene. This is believed to be due to
antioxidant interference with the body's normal use of localised free radicals
e.g. nitric oxide for cell signalling. Due to the complex nature of the
interactions of antioxidants with the body, it is difficult to interpret the
results of many experiments. In vitro testing (outside the body) has shown many
natural antioxidants, in specific concentration, can halt the growth of or even
kill cancerous cells.

In the early 1990s, it was hypothesized that oxidation of LDL cholesterol
contributes to heart disease, and several observational studies found that people
taking Vitamin E supplements had a lower risk of developing heart disease..[28]
Taken together, this led researchers to conduct at least seven large clinical
trials testing the effects of antioxidant supplement with Vitamin E, in doses
ranging from 50 to 600 mg per day. However, none of these trials found a
statistically significant effect of Vitamin E on overall number of deaths or on
deaths due to heart disease.[29]

While several trials have investigated supplements with high doses of
antioxidants, the "Supplémentation en Vitamines et Mineraux Antioxydants"
(SU.VI.MAX) study tested the effect of supplementation with doses comparable to
those in a healthy diet.[30] Over 12,500 French men and women took either low-dose
antioxidants (120 mg of ascorbic acid, 30 mg of vitamin E, 6 mg of beta carotene,
100 ?g of selenium, and 20 mg of zinc) or placebo pills for an average of 7.5
years. The investigators found there was no statistically significant effect of
the antioxidants on overall survival, cancer, or heart disease. However, a
subgroup analysis showed a 31% reduction in the risk of cancer in men, but not
women. The authors interpreted these results as suggesting that "an adequate and
well-balanced supplementation of antioxidant nutrients, at doses that might be
reached with a healthy diet that includes a high consumption of fruits and
vegetables, had protective effects against cancer in men."

[14] ^ Schumacker P (2006). "Reactive oxygen species in cancer cells: Live by the
sword, die by the sword.". Cancer Cell 10 (3): 175-6. PMID 16959608
_______________________________________________
<http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16959608>

Cancer Cell. 2006 Sep;10(3):175-6.
* Cancer Cell. 2006 Sep;10(3):241-52.

Reactive oxygen species in cancer cells: live by the sword, die by the sword.
Schumacker PT.

Department of Pediatrics, Northwestern University, Chicago, Illinois 60611,
USA.
<email address available there>

Reactive oxygen species and tumor biology are intertwined in a complex web,
making it difficult to understand which came first, whether oxidants are required
for tumor cell growth, and whether oxidant stress can be exploited
therapeutically.

Evidence suggests that transformed cells use ROS signals to drive proliferation
and other events required for tumor progression.
This confers a state of increased basal oxidative stress, making them vulnerable
to chemotherapeutic agents that further augment ROS generation or that weaken
antioxidant defenses of the cell.

In this respect, it appears that tumor cells may die by the same systems they
require.

Publication Types:
PMID: 16959608 [PubMed - indexed for MEDLINE

.

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