Check this article out by the outstanding writer Sharon Begley:
"To anyone who feels guilty for not gorging on antioxidants—actually, make that “antioxidants!,” which seems to be how grocery manufacturers think of them—redemption is nigh."
"A 2010 study in lab rats found that two popular antioxidants, quercetin (found in black and green tea, red onion, and other plant foods) and ferulic acid (in apples, artichokes, wheat, and other plants), aggravated and possibly triggered kidney cancer."
"... a new study in lab mice finds that a natural protein that boosts antioxidant levels in the blood may actually promote atherosclerosis, or clogging of the arteries. The study, in the January issue of Arteriosclerosis, Thrombosis, and Vascular Biology, offers clues about why taking antioxidants has not been shown to improve heart health. The protein Nrf2 indeed boosts antioxidants, but it also raised blood-cholesterol levels, as well as cholesterol content in the liver—both of which are excellent ways to get atherosclerosis."
There's a couple of points that need to be brought up when talking about the benefits of antioxidant supplementation. The first is "What exactly do you mean by antioxidants?"
In the studies cited above, Quercetin and Ferulic acid (hydroxycinnamic acid) are both examples of phenolic or polyphenolic antioxidant compounds. Now, the critical point here is that while they may have limited direct activity to react with free radical species or other pro-oxidants, they may also alter other metabolic pathways using mechanisms that aren't related to direct antioxidant properties. A great example of this is resveratrol, the polyphenol antioxidant in red wine and grapes--this primarily affects the activity of the Sirtuin family of enzymes, and does relatively little to actually interact with reactive oxygen species. This is an indirect example of an antioxidant, since the SIRT family members have antioxidant downstream effects on metabolism. Quercetin interferes with a lot of other enzymes, and those may be implicated in its effects independent of antioxidant activity.
The second point is "What are you trying to protect against?" Redox signaling processes are required for life, and you need a balance of antioxidants and prooxidants to better help this. This is the idea about the too much of anything is poison. Nrf2 is no different--if you overexpress a gene, it doesn't mean that it's a bad gene, it means that you messed up the normal homeostatic mechanisms at play in the cell. It's equivalent to the following: say you overfilled your car with gasoline and sprayed it all over the side of your car, and then it caught fire. You'd probably conclude that gasoline is bad for your car, which is silly--you need gas for the car to move.
The point isn't that antioxidants are bad for you (though the idea of "ANTIOXIDANTS!" is patently silly). It's that they are drugs that need to be used wisely. Labeling them as supplements does you as the consumer a disservice, because they have significant biological effects on you that may not be relate to what they say they are doing. A great example of this is St John's Wort, which is a "natural" antidepressant that also severely impairs your liver's xenobiotic metabolism pathways. We need to be careful in both directions, both under and over supplementation.
It’s always struck me as odd that you would want to ingest extra antioxidants anyway, given that oxidising agents are at the front-line of immune defence against pathogens and cancer cells ..
It's all about the dose, I presume the amounts we get from a whole food diet are wildly safe, yet the pills give us doses that approach poison
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