The right side of the heart, shown here in blue, pumps deoxygenated blood from the body to the lungs, where it can fill up with oxygen, and then the left side of the heart, shown here in red, pumps oxygen-rich blood from the lungs to the rest of the body. So, blood travels from the body, to the right side of the heart, to the lungs, to the left side of the heart, back to the body. But what if you’re still in the womb? When you’re a fetus, your lungs don’t work, because they’re filled with fluid. So, how does your heart bypass the lungs and spread the oxygen-rich blood coming in through the umbilical cord to the rest of your body? Before we’re born, we have an extra blood vessel called the ductus arteriosus, that directly connects the right side of the heart with the left side of the heart, bypassing your fluid-filled lungs—until you’re born, and you take your first breath, and this blood vessel closes. But in about 1 in 10,000 births, this blood vessel closes prematurely while the baby’s still inside, necessitating an emergency C-section.

Most cases for which there’s a known cause are thought to be related to taking anti-inflammatory drugs, like aspirin or ibuprofen. This is because the way your body keeps this blood vessel open is with a class of inflammatory compounds called prostaglandins. If you take an anti-inflammatory drug, you can undermine your body’s ability to keep it open, and it could constrict closed prematurely. That’s why most authorities recommend that these NSAID anti-inflammatory drugs be avoided in the third trimester. The likelihood anything bad is going to happen is extremely remote, but better safe than sorry.

Sometimes, this premature constriction happens even when women are not taking drugs, so called “idiopathic” cases, which is doctorspeak for “we have no idea what causes it.” If anti-inflammatory drugs can cause it, though, what about anti-inflammatory foods? A few years ago, I profiled two cases apparently caused by pregnant women drinking chamomile tea, one of which reversed. The ductus opened right back up once the tea was stopped. But the other baby had to come right out. Since then, there have been other case reports; for example, a women who had been drinking a few ounces of an acai berry drink every day or another woman who was drinking prune juice, and a violet vegetable juice containing a blend of fruits and veggies. Pregnant women should, therefore, take special care when consuming lots of these powerful anti-inflammatory berry nutrients.

What about berries themselves, and green tea, and all the other wonderful anti-inflammatory foods and beverages out there? This group of researchers in Brazil compared ultrasounds of third trimester babies’ hearts inside moms who ate a lot of these anti-inflammatory foods, to those of women who ate less and they could tell a difference. The speed of blood through the ductus in the anti-inflammatory diet moms was higher, suggesting it was narrower, just like when you pinch the opening of a hose closed and can make water shoot out faster. And, also, the right sides of the hearts of the babies in the anti-inflammatory diet moms were larger than their left sides, suggesting some blood backup, again an indicator of a tighter ductus. The researchers suggested changes in late pregnancy diets may be warranted. But critics replied that the differences they noted may not have any clinical relevance, meaning it may not matter if the vessel is a little more open or closed. And look, we don’t want to freak women out, as many of these anti-inflammatory foods may be beneficial—like cranberries for example, which may be useful in preventing urinary tract infections that can be a risk factor for premature birth. So, cranberries are attractive from a public health and cost consideration standpoint if they can prevent some premature births.

So, before cutting down on a healthy food like cranberries, we’d want some stronger evidence that they’re potentially harmful. What about confounding factors, for example—maybe women who ate lots of anti-inflammatory foods had other characteristics that could affect fetal blood flow? What we would need is an interventional trial where you take pregnant women, change their diets and see what happens. But we didn’t have such studies, until now. And, a few weeks during third trimester cutting back on anti-inflammatory foods like tea, coffee, dark chocolate, grapes, and citrus did indeed seem to open the ductus a little bit. This was just during normal pregnancies. In women whose fetuses had abnormally constricted vessels, a few weeks of removing polyphenol-rich foods reversed the ductal constriction in 96% of cases. Now, importantly, they didn’t follow these babies after birth to see if it made any difference. That complete closure happens in only 1 in 10,000 births. We’re not sure what effects just relative levels of constriction may have; so it’s too early to be instituting a ban on dark chocolate for pregnant women.

At this stage, what we’re left with is a note of caution. So, during the rest of life, I recommend piling on these healthy foods, like berries and cocoa powder, but from about 28 weeks until birth, pregnant women may want to cut back until we know more.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.

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