What could explain these very contradictory result from the other study? And there's also one that find that milk impairs tea vascular protective effect and same with dark chocolate.
The difference could be the way antioxidant capacity is measured as discussed in this study:
Food Chemistry Volume 122, Issue 3, 1 October 2010, Pages 539-545
Dual effect of milk on the antioxidant capacity of green, Darjeeling, and English breakfast teas
Svetli Dubeaua, Guy Samson, and Heidar-Ali Tajmir-Riahia
Using water soluble methods (ATBS and voltammetry) they found that milk interfered with the antioxidant activity, but if they test for lipid peroxidation milk is actually synergistic. The paper has a very good discussion about what characteristics affect the binding of polyphenols to milk proteins. (specifically size of the polyphenol molecules and hydrophobicity). These are all in vitro studies though.
Here's a response to the study where they tested vascular function:
Eur Heart J. 2007 May;28(10):1265-6; author reply 1266-7. Epub 2007 Apr 28.Addition of milk prevents vascular protective effects of tea.Pfeuffer M, Schrezenmeir J.
In the comment they state that the improvement was minor (3.5%) and they doubt that when casein is digested the catechins will remain bound in the blood (but if it is a covalent bond which some of it is according to the study posted above then that may be a problem).
I do not know if the polyphenols in tea have such an effect on the vascular system, but I know theanine has a hypotensive effect. Maybe when ingested with other proteins (e.g. milk) theanine doesn't have the effect as if it was supplemented alone (just like with l-arginine).
J Agric Food Chem. 2006 Oct 4;54(20):7940-6.Anthocyanin absorption and antioxidant status in pigs.Walton MC, Lentle RG, Reynolds GW, Kruger MC, McGhie TK.
Based on the delayed effect from the anthocyanin levels and antioxidant measurement the study by Walton et al show that it is the effect of the metabolites providing the antioxidants (or it could be due to uric acid production as I have seen in other studies). [this study was in pigs]
Polyphenols are metabolized fairly fast and some time later all is found is the metabolites. Either the original polyphenol was able to provide the benefits within a few hours or it is the metabolites who stay around for hours that provides the health benefits:
Br J Nutr. 2004 Jun;91(6):933-42.Anthocyanin metabolites in human urine and serum.Kay CD, Mazza G, Holub BJ, Wang J.
For a good back and forth on this topic:
Nature 424, 1013 (28 August 2003) | doi:10.1038/4241013a Plasma antioxidants from chocolate, Mauro Serafini, Rossana Bugianesi, Giuseppe Maiani, Silvia Valtuena, Simone De Santis & Alan Crozier
Nature 426, 787-788 (18 December 2003) | doi:10.1038/426787b Nutrition: Milk and absorption of dietary flavanols, Hagen Schroeter, Roberta R. Holt, Timothy J. Orozco, Harold H. Schmitz2 & Carl L. Keen
Nature 426, 788 (18 December 2003) | doi:10.1038/426788a Nutrition: Milk and absorption of dietary flavanols, Mauro Serafini & Alan Crozier
Overall I am inclined to believe that the matrix effect occurs (as mentioned by Schroeter et al, basically the milk protein slows down absoprtion but the polyphenols eventually reach the blood):
J Food Sci. 2007 Apr;72(3):S230-3.The effect of milk protein on the bioavailability of cocoa polyphenols.Keogh JB, McInerney J, Clifton PM.
In this study milk protein and polyphenols were found to be synergistic in terms of antioxidative effect:
Vol. 69, Nr. 9, 2004—JOURNAL OF FOOD SCIENCE
Antioxidative Properties of Commercial Fruit Preparations and Stability of Bilberry and Black Currant Extracts in Milk Products
G. SKREDE, V. BRYHN LARSEN, K. AABY, A. SKIVIK JØRGENSEN, AND S.-E. BIRKELAND
So as far as I know the bindings to proteins don't affect the antioxidant capacity of the berry polyphenols.
Here's a study showing different metabolite profiles as detected in urine but the overall amount is the same:
Br J Nutr. 2008 Oct;100(4):846-51. Epub 2008 Feb 7.The effects of milk as a food matrix for polyphenols on the excretion profile of cocoa (-)-epicatechin metabolites in healthy human subjects.Roura E, Andrés-Lacueva C, Estruch R, Lourdes Mata Bilbao M, Izquierdo-Pulido M, Lamuela-Raventós RM.
If anyone has access to this letter from the Mayo Clinic I would be interested in it:
Mayo Clin Health Lett. 2007 Jul;25(7):4.Study questions cardiovascular benefits of tea with milk.[No authors listed]
Do I eat my blueberries with yogurt or milk? No because I haven't found a need too (because I used coconut milk and the coconut milk solidifies around the frozen blueberries fairly tastily) but I wouldn't be worried. Then again all this could be wrong and the absorption profile is very important and a certain concentration has to be reached before a positive effect is induced. In this case blueberries, teas, chocolate is best taken on an empty stomach.
Edited by Sillewater, 25 August 2010 - 03:11 AM.