There is a lot of confusion among the public on antioxidants. For the most part, this is for a good reason. Many food companies put antioxidant numbers on the packages that sound good to consumers, who have no idea how to interpret them. Thus, it is increasingly important to have an understanding of what a meaningful antioxidant actually is.
A meaningful antioxidant has two characteristics (these are based on the assumption that the compound is an antioxidant):
- Found in appreciable amounts right location where there are free radicals/ROS that need to be quenched
- It is not redundant with another antioxidant that is already serving as an antioxidant
What do these mean? Let's consider the example of lycopene and vitamin E (alpha-tocopherol), which are both fat-soluble antioxidants. In vitro antioxidant assays have found that lycopene is 10-fold more effective in quenching singlet oxygen than alpha-tocopherol1. However, when you look at the concentrations found in the body, there is far more alpha-tocopherol than lycopene. For example:
LDL on average contains 11.6 molecules of alpha tocopherol and 0.9 molecules of lycopene. Thus, if we divide alpha tocopherol by lycopene 11.6/0.9 we find that there is on average 12.9 times more alpha-tocopherol than lycopene1.
Other examples in the body:
Prostate - 162-fold higher alpha-tocopherol than lycopene concentrations
Skin - 17 to 269-fold higher alpha-tocopherol than lycopene concentrations
Plasma - 53-fold higher alpha tocopherol than lycopene concentrations1
Thus, despite the fact that lycopene is a better antioxidant in vitro, since the concentration of alpha-tocopherol is so much higher in tissues (locations of need), it is likely the more meaningful antioxidant. In addition, if lycopene and alpha-tocopherol have similar antioxidant functions (fat-soluble antioxidants), lycopene’s potential antioxidant action is redundant to alpha-tocopherol’s antioxidant function and thus, also less likely to be a meaningful antioxidant. Indeed, further examination of the literature has not suggested that lycopene can act as an antioxidant in vivo, even though it is a good one in vitro1.
You may be wondering “What about the in vitro antioxidant assays, like the oxygen radical absorbance capacity (ORAC) assay that some food and supplement companies are including on their labels?” This is an example of how some companies/businesses use ORAC values to market their product(s). However, the USDA removed its table of ORAC values “due to mounting evidence that the values indicating antioxidant capacity have no relevance to the effects of specific bioactive compounds, including polyphenols on human health2.”
However, going back to the two characteristics of meaningful antioxidants, there really is no evidence that shows that a high ORAC score leads to any benefit in vivo. This is because the measure also doesn't take into account characteristics such as bioavailability. Bioavailability is the amount of a compound that is absorbed or reaches circulation. Many of these purported super antioxidants have not been shown to be absorbed or maintained in the body in a way that would suggest that they would be meaningful antioxidants.
References & Links
- Erdman, J.W., Ford, N.A., Lindshield, B.L. Are the health attributes of lycopene related to its antioxidant function? Arch Biochem Biophys, 483: 229-235, 2009.
Sozo Coffeee ORAC Comparison - http://www.sozoglobal.com/products/?...roducts/?sec=1