Friday Favorites: Benefits of Blueberries for Blood Pressure May Be Blocked by Yogurt

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

A trio of Harvard studies that followed more than 100,000 women for more than a decade found that those consuming the most anthocyanins (the brightly-colored pigments found in berries, like blueberries and strawberries) “had an 8% reduction in [the] risk of” developing high blood pressure. And the group consuming the most every day were only eating about six strawberries’ worth, or even just 11 blueberries—a tenth of a cup.

But, maybe the biggest berry-eaters just happened to have other healthy habits, and that’s the real reason they did better? After all, you’re probably more likely to sprinkle blueberries on oatmeal than on bacon and eggs. But, they controlled for whole-grain intake, and fiber and salt and smoking and exercise and a bunch of other things, and the berry benefit still remained. But, you don’t know for sure until you… put it to the test.

“A Randomized, Double-Blind, Placebo-Controlled Clinical Trial,” and, the title gives away the thrilling conclusion: “Daily Blueberry Consumption Improves
 Blood Pressure.” How can you do a double-blind trial, though, with a food? How can you convincingly create a fake placebo blueberry? They used whole blueberries—about a cup worth, but powdered them, versus a look-alike placebo powder, which had the same amount of sugar and calories as the real blueberries, but without the actual blueberries. Those in the placebo control group: no real change over the eight-week study. They started out 138 over 79, and ended up 139 over 80, whereas the real blueberry group fell from 138 over 80 to 131 over 75—a significant drop. Now, 131 is still too high. You’d like to see at least down to 120 or even 110, so blueberries alone may not cure you. However, the fact that you could get a clinically significant improvement in a killer disease by just adding a single thing to your diet is pretty impressive.

Is more better? What about twice the dose, more like two cups of fresh blueberries a day? Same kind of significant drop, but didn’t seem to work any better. So, one cup may do it. Even less may work; it’s never been tested.

Overall, there have been five interventional studies to date on the effects of blueberry supplementation on blood pressure. Put all the studies together and the results do not show “any clinical efficacy”—wait, what?! I just showed you two studies where there was this gorgeous effect. Have I been cherry-picking studies, or rather berry-picking studies? Well, if you look closely at the studies, “the blueberries in the two studies [I showed you that] detected a significant effect [were] prepared with water.” They just mixed the blueberry powder with water. However, the blueberries in the non-significant effect studies were prepared with yogurt and skim milk-based smoothies.

If you remember my blast-from-the-past video from like eight years ago, the absorption of berry nutrients can be blocked by dairy. Mix strawberries with water, and you get a nice peak in strawberry phytonutrients in your bloodstream within hours of consumption. But, if you instead go for strawberries with cream—mixing the same amount of strawberries with milk instead— significantly less makes it into your system. “The inhibitory effects of milk [are thought to] be due to [the] interaction [between the berry pigments] and milk proteins.” Yeah, but does the same thing happen with blueberries? Let’s find out.

Hard to maintain the suspense when the title just gives it away. But, indeed: the “[a]ntioxidant activity of [blueberries] is impaired by…milk.” Volunteers ate a cup and a half of blueberries with water or with milk, and the milk blocked the absorption of some phytonutrients, but not others. So, did it really matter that much? Here are the spikes in the bloodstream after blueberries with water, and here’s how much is absorbed with milk. Okay, so less. But, check out what happens to the total antioxidant capacity of your bloodstream. Eat blueberries alone, with water, and the antioxidant power of your bloodstream shoots up within an hour, and remains elevated five hours later. Okay, so with milk, you’d be thinking there’d be maybe less of a bump, right? You can say that again; not just less, but less than where you started from­. You just ate a whole bowl of blueberries and ended up with less antioxidant capacity in your body, because you ate them with milk. No wonder mixing blueberries with yogurt or milk may abolish the blood-pressure lowering benefits.

Interestingly, “full-fat milk” may inhibit nutrient absorption the most, similar to what one finds adding milk to tea: twice the reduction in in vitro antioxidant values with whole milk compared to skim milk, which is weird because we always thought it was the milk protein that was the culprit. This suggests there may be some nutrient-blocking involvement from the dairy fat as well.

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• Cassidy A, Bertoia M, Chiuve S, Flint A, Forman J, Rimm EB. Habitual intake of anthocyanins and flavanones and risk of cardiovascular disease in men. Am J Clin Nutr. 2016;104(3):587-94.
• Cassidy A, O'reilly ÉJ, Kay C, et al. Habitual intake of flavonoid subclasses and incident hypertension in adults. Am J Clin Nutr. 2011;93(2):338-47.
• Johnson SA, Figueroa A, Navaei N, et al. Daily blueberry consumption improves blood pressure and arterial stiffness in postmenopausal women with pre- and stage 1-hypertension: a randomized, double-blind, placebo-controlled clinical trial. J Acad Nutr Diet. 2015;115(3):369-77.
• Basu A, Du M, Leyva MJ, et al. Blueberries decrease cardiovascular risk factors in obese men and women with metabolic syndrome. J Nutr. 2010;140(9):1582-7.
• Zhu Y, Sun J, Lu W, et al. Effects of blueberry supplementation on blood pressure: a systematic review and meta-analysis of randomized clinical trials. J Hum Hypertens. 2017;31(3):165-171.
• Xiao D, Sandhu A, Huang Y, Park E, Edirisinghe I, Burton-freeman BM. The effect of dietary factors on strawberry anthocyanins oral bioavailability. Food Funct. 2017;8(11):3970-3979.
• Serafini M, Testa MF, Villaño D, et al. Antioxidant activity of blueberry fruit is impaired by association with milk. Free Radic Biol Med. 2009;46(6):769-74.

Image credit: Veganbaking.net via Wikimedia. Image has been modified.

Motion graphics by Avocado Video.