Previous laboratory and animal research has shown that exogenous antioxidants can help prevent the free radical damage associated with the development of cancer.
Research in humans has not demonstrated convincingly that taking antioxidant supplements can help reduce the risk of developing or dying from cancer, and some studies have even shown an increased risk of some cancers.
Antioxidants are chemicals that block the activity of other chemicals known as free radicals. Free radicals are highly reactive and have the potential to cause damage to cells, including damage that may lead to cancer.
But employing antioxidants could backfire - at least in the case of omega 6 fatty acid that have been found to promotes cancer in animal studies.
In their study, researchers found that vitamin E actually increased specific damage linked to omega 6 fatty acids.
The vitamin promoted the formation of an "adduct", a structure that links a chemical to DNA and which may cause mutations, said researchers from Georgetown Lombardi Comprehensive Cancer Center.
On the other hand, in the setting of omega 6, the antioxidant green tea polyphenol reduced formation of another commonly found "adduct" from omega-6 fatty acid - suggesting it may have beneficial health effects.
"The third antioxidant tested, alpha-lipoic acid - found in spinach and broccoli and proven to have anti-cancer properties - had no effect on either of the two 'adducts' studied," said Fung-Lung Chung, a professor of oncology at Georgetown Lombardi Comprehensive Cancer Center.
The study was designed to understand why omega 6 polyunsaturated fatty acids - found in many cooking oils - promote liver cancer, while their cousin, omega 3, helps prevent cancer.
Researchers examined formation of DNA-damaging adducts in liver cells treated with omega 6.
One of those adducts, Y-OHPdG, is well known, but the research team discovered a second one - DHHedA.
"This study revealed that DHHedA is a novel type of DNA damage, found in the tissues of rodents and humans, that is caused by omega 6 polyunsaturated fatty acid," Chung explained.
In rats engineered to develop liver cancer, green tea polyphenols reduced formation of Y-OHPdG adducts, and vitamin E increased production of DHHedA adducts.
"Our findings are beginning to shed light on why omega 6 fatty acids are believed to have negative health effects," Chung noted.
But we have a long way to go before we can make definitive health claims on these antioxidants, he told the gathering at the American Association for Cancer Research (AACR) annual meeting 2014 in SanDiego, California this week.
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