I'm not sure you can apply those findings regarding antioxidants. NAC isn't itself an antioxidant, but a prodrug for an amino acid that is the rate limiting fac

I'm not sure you can apply those findings regarding antioxidants. NAC isn't itself an antioxidant, but a prodrug for an amino acid that is the rate limiting factor in producing glutathione, the bodies primary endogenous antioxidant. Presumably if you're already "full" on glutathione, the NAC does nothing.