Michael Greger M.D. FACLM, asks in his daily blog, “What is the optimum dose of wild blueberries to eat at a meal?”
A single serving of blueberries can help mediate the arterial dysfunction induced by smoking a cigarette. Researchers investigated the effect of a single serving of frozen blueberries on young smokers. As you can see at 0:19 in my video Benefits of Blueberries for Artery Function, when you smoke a single cigarette, the ability of your arteries to relax naturally drops 25 percent within two hours. But, if you eat two cups of blueberries a hundred minutes before smoking, that same cigarette causes less than half the damage, demonstrating that a single, big serving of frozen blueberries could counteract the artery dysfunction induced by smoking. Of course, it should be noted that “blueberry consumption cannot be considered a means of preventing health consequences due to smoking; this can only be realized by smoking cessation and/or prevention,” i.e. not smoking in the first place.
Two cups of blueberries are a lot, though. Yes, you could easily drink them in a smoothie, but what do you think is the minimum dose to achieve that effect? We didn’t know until a group of British researchers decided to put it to the test. In order to do a double-blind study, they had to create a fake blueberry drink for the placebo control. They used freeze-dried wild blueberry powder to give people the equivalent of three-quarters of a cup, one and a half cups, one and three-quarter cups, about three cups, or four cups of fresh wild blueberries. The researchers concluded that “blueberry intake acutely improves vascular [arterial] function…in an intake-dependent manner.” So what’s the optimal intake? As you can see at 1:32 in my video, nothing happened after the placebo. After eating one and three-quarter cups’ worth of blueberries, however, there was a big spike in artery function improvement within just one hour of consumption and that seems to be where the effect maxed out. Less than a cup is good, but between one and two cups seems better, with no benefit going beyond that in a single meal.
Can you cook them? What if you baked with them, for instance? As you can see at 2:00 in his video, the same remarkable improvement in artery function was seen with blueberries baked into a bun. The only difference is the spike happened an hour later since solid food passes more slowly through your stomach.
If you eat blueberries week after week, you also get chronic benefits, in terms of reduced artery stiffness and a boost in your natural killer cells, which are one of your body’s natural first lines of defense against viral infections and cancer. How can blueberries have all these amazing effects if the anthocyanins—the blue pigments in blueberries purported to be the active ingredients—hardly even make it into our system? Indeed, women were given more than a cup of blueberries to eat, and the researchers couldn’t find hardly any in their bloodstream or flowing through their urine.
At 2:47 in his video, you can see a chart called a chromatogram. The spikes show all the anthocyanin peaks in blueberries. Before eating blueberries, there is no sign of the pigments in the participants’ blood, which makes sense because they hadn’t been ingested. After one hour of eating them, however, you start to see the spikes appear, and, a few hours after that, they become a bit more distinct. All in all, though, just a few billionths of a gram per milliliter show up. So, “either anthocyanin are extremely potent and, therefore, active at low serum [parts-per-billion blood] concentrations…or their dietary occurrence or bioavailability has been underestimated.” Researchers decided to radioactively tag them and trace them throughout the body.