I don’t know how I missed this issue for so long, but I stumbled across it the other day and still can’t decide if it’s something worth worrying about, or if it’s just another chance to overcomplicate things by “sweatin’ the small stuff”.
The short version of this study on polyphenols and milk is that they fed some people blueberries with water and observed the levels of two major polyphenols as well as the “antioxidant capacity” of their blood for five hours. Then they did the same thing except they gave the subjects blueberries and milk. The milk did three things: 1) “flattened” the curve for serum levels of polyphenols, i.e., slowed down the absorption of both polyphenols, 2) non-trivially reduced the area-under-the-curve for serum levels of one of the polyphenols, and 3) completely muted the sharp increase in antioxidant activity that they saw in the blueberry/water group. As a person who consumes blueberries nearly every day because of their superfood status, this worried me because while I don’t consume them with milk, I frequently consume them with either a protein supplement or in greek yogurt, both of which contain healthy doses of casein, which is one of the two kinds of protein in milk and the thing that the researchers hypothesized was the culprit.
To be sure, this looks like a complicated issue. The Wikipedia blurb on this issue reads
A study of Charité Hospital in Berlin by Lorenzo et al., published in The European Heart Journal, showed adding milk to tea causes the casein to bind to the molecules in tea that cause the arteries to relax, especially a catechin molecule called EGCG, although a more recent study by Reddy et al. (2005) suggests the addition of milk to tea does not alter the antioxidant activity in vivo, and the cardiovascular effect remains controversial. A study published in the journal Free Radical Biology and Medicine found that consuming 200 mL of whole milk (vs. water control beverage) abolished the 6.1% increase in plasma reducing and chain-breaking antioxidant potential that resulted from consuming 200 g of blueberries, and reduced the peak plasma concentrations of caffeic and ferulic acids, “as well as the overall absorption (AUC) of caffeic acid.” The authors did not specifically associate this with the milk’s casein content, however. Reviewing previous studies on the impact of milk on absorption of polyphenols, the authors say, “It is a matter of fact that the discrepancy of the results in humans is remarkable, with half the reports suggesting a lack of effect and the other half suggesting an inhibitory effect of milk.”
Also, at least one study showed that milk doesn’t blunt at least one of the major benefits of cacao consumption, but I’m not sure if the cholesterol/cardiovascular benefits of tea and cacao are necessarily thought to be mediated through their polyphenols. The second page of this post over at Longecity has a useful discussion.
So, unfortunately, there is just enough information here to be confusing. However, if it’s not too inconvenient for you, perhaps it’s worthwhile to eat your berries either before or well after you eat your dairy or other source of milk proteins.