From Mother’s Lungs To Baby’s Body

11:27 minutes

woman holding a baby close and looking at it
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In pregnancy, the placenta is a critical organ. It allows the fetus to obtain nutrition and oxygen, and, in the process, filters harmful substances from the mother’s body before they enter the growing baby’s system.

But our understanding of how protective that placenta is has been changing. Some ingested substances, like alcohol and pthalates, are known to cross the boundary and cause harm.

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And in the case of air pollution, a mother’s exposure is increasingly correlated with health problems in the infant, from cardiovascular to neurodevelopment. But how do inhaled particles lead to these problems? New research in the Journal of the American Medical Association Network Open this month points to one potential mechanism: changes in the thyroid hormones, which are critical to early development. What’s going on—and what can be done to protect the most vulnerable from potentially lifelong health effects?

Carrie Breton, a co-author on the new research and a professor at University of Southern California, describes her findings.

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Segment Guests

Carrie Breton

Carrie Breton is an associate professor of Preventative Medicine in the Keck School of Medicine at the University of Southern California in Los Angeles, California.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Coming up, we’re going to talk about how Pakistan’s Indus River is starting to dry up, and why that could catapult the region into war. But first, in pregnancy the placenta, as you know, is a very critical organ. It allows the fetus to obtain nutrition and oxygen, and in the process, filters harmful substances from the mother’s body. But our understanding of how protective that placenta is has been changing.

Some ingested substances are known to cross the boundary and cause harm, but how about alcohol or phthalates? And in the case of air pollution, the mother’s exposure is increasingly correlated with health problems in the infant, from cardiovascular to neurodevelopment. But how do inhaled particles lead to these problems? New research in the Journal of the American Medical Association network, open this month, is pointing to one potential mechanism, changes in the thyroid. What’s going on and what can be done to protect the most vulnerable from potentially lifelong health effects? My next guest is an author on the research, Dr. Carey Brenton is associate professor of preventive medicine at USC in Los Angeles. Welcome, Dr. Brenton.

CAREY BRENTON: Thank you very much, and good afternoon.

IRA FLATOW: Good afternoon to you. What got you looking at air pollution and the thyroid?

CAREY BRENTON: Well, believe it or not, I grew up in Southern California in the 80s. And I grew up living through smoggy alert days and swimming in the summer and feeling that really icky feeling in your lungs after a bad air day. So I’ve been thinking about air pollution for many years now. And I really want to understand how early in life does because air pollution affect us? So we wanted to look in the room and ask the question at the earliest stage of life, can air pollution affect our health? And we started with looking at the thyroid, because the thyroid is very important in metabolism and fetal brain development.

IRA FLATOW: And you saw elevated levels of this hormone, thyroxine, in infants whose mothers were exposed to more air pollution. How could that affect the child’s health later in life?

CAREY BRENTON: Well, we know that thyroid hormones are really important in metabolism and in brain growth. And we already know that having either too little hormone or too much hormone can have bad effects. That’s, in fact, why the state of California and other states have a newborn screening program that tests newborns for thyroid hormone, because if the baby has too little hormone, they can intervene. They can give medications, and they can prevent the cognitive deficits from happening. So there’s a lot that’s already known about thyroid hormone levels and how they affect health. So if the environment, now, is affecting those levels, it may be skewing our systems and making us more vulnerable for these health effects.

IRA FLATOW: Mhm. Now, to be clear, you saw hormonal changes, but this isn’t proof of direct harm yet. Right?

CAREY BRENTON: Correct, yes.

IRA FLATOW: Even though we know from other work that there are harms, right? Tell us why.

CAREY BRENTON: Well, in this study, all we measured was the thyroid hormone, T4, directly. And we measured it in the newborn. So what we showed was that higher particulate matter is associated with higher thyroid hormone levels. But we did not, in this study, relate that change in thyroid hormone levels to any child health outcome later in life. That’s actually something we would like to do as a next step.

IRA FLATOW: Does it seem to matter what kind of air pollution we’re talking about? Like particulates, or chemicals, or small particles, soot, whatever?

CAREY BRENTON: Yes, it does matter. We looked at both the particulate matter as well as ozone and nitrogen dioxide. So several different ambient pollutants that are very typically regulated and monitored across the nation and in Los Angeles. And we saw these effects of particulate pollution, not with ozone or nitrogen dioxide.

IRA FLATOW: Do you have any clues yet, of the mechanism?

CAREY BRENTON: You know, there are a lot of theories and there are a lot of investigations into this. One of those is that air pollution, in general, may be increasing inflammation throughout the body, and that may have its own set of cascading effects as the baby is developing.

IRA FLATOW: Does it concern you any that you’re seeing more and more wildfires now that might not be a factor in years past?

CAREY BRENTON: Yes. Wildfires emit a lot of particulate matter. They may be different sizes of particulate matter and different compositions than vehicle exhaust and diesel exhaust, but fundamentally, particulates come from incomplete combustion and things that burn. And wildfires burn a lot of stuff, and they emit tons of particles into the air.

IRA FLATOW: Is our understanding of air pollution and health changing from what it used to be?

CAREY BRENTON: Well, I think what I can safely say is that we know air pollution is bad for us. And we’re finding that even at the earliest moments in life, it may be bad for us. What I can tell you is that, in Southern California, we’ve been trying to reduce air pollution for decades now, and we’ve been successful in doing that. The levels have come down in the last decade, in part because we’ve regulated emissions. And the nice thing about this is that we’ve also seen corresponding increases in kids’ health when air pollution levels come down. So we know it works, and we know we can do something about it.

IRA FLATOW: That’s interesting. You really have enough data now to know that in enough years that it does matter.

CAREY BRENTON: Yes, yes. Just in our own work, we followed a cohort of children called the Children’s Health Study for more than 20 years. And the whole purpose of that study was to look at air pollution’s effects on kids’ health.

IRA FLATOW: Do we know if particles are actually crossing the placenta, or is there some intervening mechanism?

CAREY BRENTON: We don’t know that with any certainty. And I think it’s going to be very dependent on what size particle we’re talking about, and whether the placenta can filter that out and be that barrier. Or also, whether in the mom, the particles cause an indirect effect and then all those cascading chemicals and molecules that change in the mom can pass the placenta, even if the particle itself doesn’t.

IRA FLATOW: You know, I don’t have to tell you, you’ve already told me that you’ve grown up in Southern California where it’s smoggy and polluted. It’s still in a lot of places now. And in those days, we always had an ozone alert, right?


IRA FLATOW: We tell the elderly not to go out, or to breathe the air, or to stay indoors. Should we be saying that to pregnant mothers now? Be careful.

CAREY BRENTON: Yes. You know, I would say it couldn’t hurt. And if you’re concerned, and you’re a pregnant mom, you can check daily the air quality index. And if you see that it’s a really bad air day, you might want to change your behavior. You might want to not go out and exercise really heavily. You might want to walk your dogs on a quieter street, away from heavy traffic. So there are little things that you could do.

IRA FLATOW: No, I’m saying, you know, as part of what you see on the weather forecast that night. You know, there are these warnings. Why not include in these warnings, to pregnant people?

CAREY BRENTON: Well, they do say for sensitive sub-populations. So if you want to consider pregnancy a sensitive population, then yes. I mean, you might want to consider it. I think it’s sort of an individual level decision.

IRA FLATOW: Is there any obstacle for you to doing more studies on this? I’m going to give you the $64 question I give to a lot of my researchers. If you had an unlimited blank check, and I have one right here in my pocket for you, what would you like to study? What would you need to know, how would you do that?

CAREY BRENTON: Well, I would continue to address the broader question of, can the environment affect fetal development? And what is that tied to 10 years, 20 years down the line as we become adults? Are we now going to be at increased risk and more susceptible for all of these things that we’re dealing with? And we could start with the thyroid. There’s a lot more we could do with understanding the thyroid itself, looking at it more holistically. Looking at the difference between how it affects mom’s thyroid and baby’s thyroid together, and disentangling that. But there are also other pollutants one could ask the same questions about.

IRA FLATOW: Possibly outgassing of rugs or things like that? Or plastics in the home, or?

CAREY BRENTON: Absolutely. I really addressed outdoor air pollution in this particular publication. Indoor air pollutants and the sources of those is a whole other ballgame.

IRA FLATOW: Yeah. Something we should be thinking about, though? For pregnant people.

CAREY BRENTON: Definitely.

IRA FLATOW: Yeah. Is there any phase of pregnancy– you know, I’m assuming that the earlier in pregnancy, the first trimester, is more important than others? Or am I being wrong about that?

CAREY BRENTON: Well actually, we actually tried to address that question specifically in this publication. We looked at month by month exposures in pregnancy to see if we could find that one month mattered the most in terms of being exposed. And what we really found was that, actually, most of pregnancy matter. Exposure anywhere from mid to late pregnancy, not quite as much in very early pregnancy. And that might have something to do with the fact that the fetal thyroid does doesn’t actually develop and start kicking in and producing its own thyroid until the second trimester.

IRA FLATOW: Is there thoughts that you might give pregnant moms thyroid pills, or injections, or anything like that to measure the level in the fetus? And say, well we need to have some more or less?

CAREY BRENTON: Well, I think there’s a lot of monitoring of that already. So if a pregnant woman’s thyroid levels fall within what are clinically normal ranges, you wouldn’t need to do anything, anyway. But that’s an interesting thought. Some women who have a thyroid disease going into pregnancy, they are already monitored for that. And yes, they will be monitored and they try to adjust those levels.

IRA FLATOW: Have you noticed that air pollution is getting any better? I mean, better meaning less of it.

CAREY BRENTON: Right, well, that depends on where you are, right? So in Southern California, yes we’ve had reductions in our air pollution levels. But in many other places around the world, the air pollution is going up.

IRA FLATOW: Are pregnant moms taught about this? Do their doctors know about air pollution as a potential hazard?

CAREY BRENTON: I don’t think, generally speaking, that there is a great level of discussion about environmental harm such as air pollution when you’re in the doctor’s office.

IRA FLATOW: All right. Well maybe we started one now, today, Dr. Brenton.

CAREY BRENTON: Yes, maybe. That would be great.

IRA FLATOW: Dr. Carey Brenton, associate professor of preventive medicine at the USC in Los Angeles. Good luck to you. Thank you for being so informative with us today.

CAREY BRENTON: Thank you very much.

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