In my opinion free oxygen scavengers really are universal agents for treating a lot of diseases.Everything depends on dosage - each drug became a poison. It seems to me further research needs to be done and present evidence-based findings.

Formation of free radicals inside our bodies may cause several diseases including cancer. Antioxidants will act as scavangers of free radicals. This does not mean that they will be necessarily helpful as supplements of drugs for a patient who is already suffering. Antioxidants, within their natural contexts, may strengthen a healthy person against diseases and that is why medical doctors keep on encouraging the public to eat more fresh fruits& vegetables. Isolating antioxidants from their natural setting & giving them in high doses may turn out to be counterproductive as what was found in a research in Finland ( using more beta-carotene for smokers increased the risk of lung cancer). The human body is a weak object; a slight increase of a drug may turn it to a lethal dose.

link site;

.Antioxidants and Cancer Prevention - National Cancer ...

www.cancer.gov/about.../antioxidants-fact-sheet

National Cancer Institute

I think, over use of antioxidant will definitely result adverse effects and may be cancer as well. 

Hello Abdul, thanks for pointing to the link from the NCI, which was not complete. Here I add the complete version, as well as a citation from its text, which I think is a highly reliable source:

"Overall, these nine randomized controlled clinical trials did not provide evidence that dietary antioxidant supplements are beneficial in primary cancer prevention. "

As I mentioned in a similar discussion some time ago: it appears to be dangerous for smokers trying to prevent cancer - and could result in the opposite.

http://www.cancer.gov/about-cancer/causes-prevention/risk/diet/antioxidants-fact-sheet

In their 2007 article, Bjelakovic et al raised concern about antioxidant supplements. This concern has often been repeated uncritically.

Nutrients should be given according to individual deficiencies, diet and exposure to toxins and radioactivity, rather than giving the same supplements to everyone, without assessing deficiencies. Assessment can done, using signs and symptoms of deficiency, or by scrutinising diets, or by laboratory testing. Randomised trials do not address individual needs.

The British Government publishes studies of deficiencies in the population, which are common.

Supplements used in disease and health should be analysed separately.

Drug companies provided supplements for 54 trials out of 68 studied by Bjelakovic. These supplements are often of poor quality, with undesirable excipients like Sunset Yellow, carrageenan, aspartame or sodium laurel sulphate.

Some of the 21 rejected, mostly smaller trials may have been less well funded, because not sponsored by drug companies, and they may not have used synthetic supplements.

Why were studies on heart attack, pre-cancer or non-melanoma skin cancer included, but not other cancers?

Excessive vitamin C reduces sulphate conjugation of oestrogen, perhaps increasing the risk of oestrogen dependent cancers in those whose sulphate conjugation is poor.

Antioxidants should be used in combination. Vitamin E is protective against vitamin A toxicity. In the absence of vitamins C and E and selenium, oxidative stress cleaves beta carotene into harmful chemicals. Synthetic trans beta carotene blocks the action of more valuable carotenoids and cis beta carotene.

Synthetic vitamin E is only L and D alpha tocopherol. Vitamin E comprises 8 D form tocopherols and tocotrienols. Alpha tocopherols may block other forms, and the L form may block the D.

Vitamin E was found to dramatically reduce repeat heart attacks, but non-significantly increased mortality. Is this because it interacts with drugs like warfarin? Vitamin E is pro-oxidant in the absence of coenzyme Q10, which statin drugs deplete.

A study of antioxidants should include coenzyme Q10, alpha lipoic acid, vitamin B2 which recycles glutathione, and manganese, copper and zinc, which are in types of superoxide dismutase.

Some trials used excessive doses. 13 out of 15 of the 47 studies with high doses of over 30mg beta carotene, over 20,000IU of vitamin A, or over 500IU of vitamin E show a relative risk of over 1. Only 16 out of the 32 lower dose studies show a relative risk of over 1. We can conclude only that excessive intake is risky.

Selenium was significantly inversely associated with mortality. In the abstract "inversely" is omitted.

Polypharmacy is a problem for nutrients as well as drugs. People may take a multivitamin/mineral, selenium with vitamins A, C and E, and cod liver oil, leading to toxic levels of vitamin A and selenium. Taking selenium and snacking on Brazil nuts may also be harmful.

Studies like this show that unintelligent use of antioxidants is unwise. Nutrients work as a team, and should be supplemented together. Individual needs should be considered. Supplements should be of good quality. Participants should not be overdosed. Care should be taken over drug-nutrient interactions. A study on a few antioxidants should not be used to judge all antioxidants.

Bolland et al have raised similar issues about calcium supplements. Why are people given high doses of calcium carbonate, when they are consuming much milk, cheese and yogurt? If their bones are fragile it is more likely they need vitamins K2 and D3 and magnesium, and to avoid cola drinks.

If you want to test a new train, you do not employ a bus driver or an airline pilot to drive it. If you want to study nutrients, make sure you have someone who understands nutrition in charge, and not someone who only understands drugs.

Regarding antioxidant supplements, the following question I earlier asked on ResearchGate seems relevant:

"Is there a difference between "natural" and "synthetic" vitamins when it comes to safety and efficiency?"

https://www.researchgate.net/post/Is_there_a_difference_between_natural_and_synthetic_vitamins_when_it_comes_to_safety_and_efficiency

Related question:

How effective are modern cancer drugs? https://www.researchgate.net/post/How_effective_are_modern_cancer_drugs

A possible supplement cocktail for cancer patients is:

vitamin E as tocotrienols rather than tocopherols

vitamin B2 to recycle glutathione

vitamin B2 to recycle glutathione

coenzyme Q10 as ubiquinol rather than ubiquinone

natural mixed carotenoids rather than beta carotene

selenomethionine rather than selenite

vitamin C

vitamin D

L-arginine

omega three fatty acids as alpha linolenic acid rather than eicosapentaenoic acid,

and avoid fructose and vitamin B1, as promoters of DNA production for new cancer cells.