Jul 21, 2013 - One of biochemistry's founding fathers, Linus Pauling, advocated the use of the ... compounds, but the word 'antioxidant' is just a general descriptive term because each are distinct chemical entities with different modes of ...
7/21/2013
10 MISCONCEPTIONS ABOUT ANTIOXIDANTS Excitement around antioxidants has diminished, replaced by polarised views and misconceptions that have started to impede industry use of the ingredient in supplements and drugs, scientists suggest.
Two scientists from Maastricht University in the Netherlands have written a review to dispel ten misconceptions about antioxidants. “Few scientific subjects have generated as many controversial opinions as antioxidants have,” Aalt Bast and Guido RMM Haenen wrote. “For several decades, we have noticed that the antioxidant pendulum appears to swing vigorously from ‘only healthy’ to ‘extremely toxic’, and from ‘natural antioxidants are best’ to ‘antioxidants cannot act’.” “The squabbling parties do not seem to listen to counter-arguments. Erroneous statements are not corrected, and thus the pendulum oscillates to the extremes,” they said. The scientists said this has hampered research in the field and confused both scientists and consumers and in the long-term could lead to missed opportunities when it comes to use of the ingredient in supplements and drugs.
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1: ANTIOXIDANTS CURE ANY DISEASE Antioxidants have been linked to preventing cellular damage induced by reactive oxygen species (ROS) – involved in numerous diseases. Subsequently it was suggested that antioxidants could prevent and treat many diseases. The scientific community now knows that although antioxidants are able to block ROS in a lab setting, there is little conclusive evidence that they can cure diseases associated with ROS in the body, the review said. ”The expectations for antioxidants were set too high and it was apparent that these compounds cannot remedy everything. Moreover, unrealistic health claims disappointed consumers and scientists.”
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2: ANTIOXIDANTS INCREASE MORTALITY A recent meta-analysis of selected randomised clinical trials concluded that antioxidant supplementation increased all-cause mortality. However, this conclusion was refuted after re-examination showed that none of the studies had mortality as a primary outcome, the review said. “Articles on antioxidants and mortality have received much attention… We should not place too much credence in unbalanced alarming news…Instead of the polarized view whereby antioxidants are either good or bad, a high benefit-risk ration would be a more appropriate approach to evaluate antioxidants.”.
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3: THE MORE THE BETTER One of biochemistry’s founding fathers, Linus Pauling, advocated the use of the antioxidant vitamin C in doses of 1000mg to optimize health – way above the recommended dietary allowance of 75-90mg/day. However, a solid scientific justification with clinical studies supporting the assumed health benefit of mega doses of vitamin C is lacking, the review said. “Administration of high doses of antioxidants might explain the increased toxicity that is sometimes reported.” “Clearly, ‘the more the better’ is not the case. Identification of an optimal dose with a high benefit-risk ratio is required, along with adequate knowledge of the biotransformation of antioxidants.”
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4: AT HIGH DOSES, ANTIOXIDANTS BECOME PRO-OXIDANTS There is an idea that when used in high doses, antioxidants can become pro-oxidant but research into ascorbic acid contradicts this theory. At low concentrations ascorbic acid behaves as a pro-oxidant but at high concentrations it becomes an antioxidant, the review said. “This contradicts the idea that a high concentration of an antioxidant always has a pro-oxidant effect.” “There seems to be confusion between the high dose relationship to toxicity according to Paracelsus and the notion of pro-oxidant behaviour. Nevertheless, this misconception persists.”
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5: ANY ANTIOXIDANT WILL DO Antioxidants act by delaying or preventing the oxidation of other compounds, but the word ‘antioxidant’ is just a general descriptive term because each are distinct chemical entities with different modes of action for their effects. Antioxidants can be thiols, phenols, and amines and may be either hydrophilic or lipophilic and they all have unique (bio-) chemical profiles, the review said. “Different antioxidants display different biological effects, and for specific pathological conditions the right antioxidant needs to be selected.”
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6: THEORETICALLY, ANTIOXIDANTS CANNOT BEHAVE AS SUSH It is argued that antioxidants cannot act faster with radicals than endogenous (bio-)molecules, and are therefore inactive.
However, site-specific scavenging and indirect activity (such as anti-inflammatory activity) can occur, even with extremely reactive hydroxyl radicals, the review said. “Without antioxidants, life in an aerobic environment would be impossible. Antioxidants do act. Their action has been established by determining their effect on biomarkers reflecting oxidative damage.”
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7: ANTIOXIDANT STATUS MEASURES HEALTH The Trolox equivalent antioxidant capacity (TEAC), oxygen radical absorbance capacity (ORAC) and ferric reducing ability of plasma (FRAP) are methods used to determine overall antioxidant status in biological and food samples. Antioxidant status in blood plasma was promoted as an ideal biomarker because it reflects the antioxidant capacity of all antioxidants present in a sample. However, antioxidant status measurements lack specificity, the review said. “Antioxidant status might be useful as an indicator of disease severity; however, it does not take into account the unique biochemical profile of specific antioxidants.”
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8: ONCE USED, ANTIOXIDANTS ARE INACTIVE There is an assumption that once oxidised, an antioxidant loses its power – which seems quite logical, said the review. However, this is not entirely correct because some antioxidants can remain quite active as scavengers when oxidized – like dihydrolipoic acid. “Antioxidants function in a network and regeneration of oxidized antioxidants frequently occurs.”
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9: NATURAL ANTIOXIDANTS ARE SUPERIOUR Chemophobia is widespread and natural antioxidants, frequently denoted by the prefix ‘bio’ are regarded as superior to chemically synthesised antioxidants by many. Consumers associate ‘bio’ with natural and therefore safety, said the review. While some natural forms of certain compounds are more effective than their synthetically derived counterparts, many synthetic versions of these natural forms are identical. For example R,R,R-a-tocopherol – the natural form of alphatocopherol is identical to the synthesized R,R,R-a-tocopherol. “This is also true for bio-vitamin C which is bioequivalent to chemically synthesized L-ascorbic acid.”
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10: ANTIOXIDANT DRUGS DO NOT WORK Many drugs have antioxidant activity even if they haven’t been specifically designed to, although the significance depends on the compound used and pathology involved. While it can be difficult to establish direct and acute effects of scavenging antioxidant compounds, the effect of antioxidants is particularly clear in situations in which radical formation and subsequent damage are also evident, the review said. “The paradox ‘antioxidants do not work’ because they cannot display antioxidant activity and that they at the same time cause toxicity and even premature mortality via antioxidant activity, is contradictory.”
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The proper antioxidant balance
Life-long exposure to oxygen poses the major health risk to aerobic life forms. To cope with oxygen toxicity, antioxidants are vital. The decay of aerobic life by oxygen leads to disease and can be delayed by appropriate antioxidant measures. Clear pharmacological responses should not be expected from antioxidants. The efficacy of antioxidants is found to their ability to strengthen homeostasis, to increase the ability to adapt.
“What a shame it would be if the design and development of new antioxidant foods, supplements, nutraceuticals, diets and drugs were to cease because misconceptions prevail.”
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Sources
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Trends in Pharmacological Sciences Published online ahead of print, doi: 10.1016/j.tips.2013.05.0104 Ten misconceptions about antioxidants Authors: A. Bast and G. RMM. Haenen
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http://www.nutraingredients.com/Research/10-misconceptions-about-antioxidants Bast, A., & Haenen, G. R. (2002). The toxicity of antioxidants and their metabolites. Environmental toxicology and pharmacology, 11(3), 251-258. http://www.sciencedirect.com/science/article/pii/S1382668901001181 Haenen, G. R. M. M., & Bast, A. (2002). The use of vitamin supplements in selfmedication. Therapie, 57(2), 119-122. http://www.ncbi.nlm.nih.gov/pubmed/21782609
http://www.sciencedirect.com/science/article/pii/S0165614713000989
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