Podcast: Childhood obesity often starts before the age of 5

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Mr. Barrett Whitener: From the National Institutes of Health, I’m Barrett Whitener and this is Research Developments, a podcast from the Eunice Kennedy Shriver National Institute of Child Health and Human Development.

A recent study showed that overweight kindergarteners were four times as likely as normal weight children to become extremely overweight, or obese, by the eighth grade. The results suggest that by focusing obesity prevention efforts on children who were overweight by the age of 5, we can help children who are most susceptible to becoming obese later in life.

My guest today is Dr. Solveig Cunningham, the lead author of the study. Dr. Cunningham is assistant professor in the Hubert Department of Global Health at Emory University. She is on the phone to tell us more about the results of the study, which was funded by the NICHD. Thank you, Doctor, and welcome.

Dr. Cunningham, what new information did you set out to find about childhood obesity?

Dr. Solveig Cunningham: So, we know quite a bit about obesity in terms of the prevalence—how many children are obese at each age, over time, and across age groups. So what we really wanted to understand was the incidence of obesity; so what that tells us is: how did kids become obese? At what ages? Which are the groups that are most vulnerable to becoming obese? So our focus was on this progression to obesity during childhood, and this focus allows us to better understand the patterns of obesity and perhaps, hopefully, where we can intervene.

Mr. Whitener: Now, what if anything was known about the incidence of childhood obesity prior to your study?

Dr. Cunningham: So not a whole lot. There have been a few studies that have looked at the incidence of obesity especially during the transition to adulthood, so among older kids, and there were some older studies, but there hadn’t been much focus on it actually for the past few years. Part of the reason, I think, is that your required data that follows kids over time to be able to look at incidence, to be able to look at when they become obese, and so we had the opportunity to do this using this large, nationally representative, longitudinal dataset that followed kids from kindergarten through eighth grade.

Mr. Whitener: Can you tell us a little bit more about how you measured the incidence of childhood obesity using that dataset?

Dr. Cunningham: Yes, as part of that data collection, that program had actually measured kids in schools and looked at their height and their weight, and so we used those data using standard CDC cutoff standard measurements for what is overweight and what is obese. Now, if we think about ourselves as adults, we have these cutoffs—that we’ve often learned about: For adults, a BMI or body mass index of 25 is considered overweight, and a body mass index of 30 and above is considered obese. With kids, it’s a little bit more complicated, because they are also growing and are supposed to be growing, and so the focus in measuring kids is seeing where they are compared with other kids of the same age and of the same gender, and seeing whether they are high among those dimensions.

Mr. Whitener: You mentioned that your study was focusing on the incidence of childhood obesity, or exactly when a child becomes obese and how that develops over time. Your study also found some more information about who was most affected by childhood obesity, or the prevalence of childhood obesity. Could you tell us a little about that?

Dr. Cunningham: Yes, so we were also able to look at a few characteristics of the kids and track incidence, track the occurrence of obesity among those groups. So we looked at socioeconomic status— just very simply in terms of cutting the population into quintiles. So, looking at the socioeconomic status and then also looking at race/ethnicity, and finally at weight at birth—so those are the main characteristics that we were focused on. And we found some differences there, we found that African American and Hispanic kids had higher incidence of becoming—basically were more likely to become obese between kindergarten and eighth grade than non-Hispanic white kids.

We also found that children from the wealthiest families were much less likely to become obese during elementary and middle school compared with children from all other socioeconomic strata. Then, we found that children who had been large at birth were also more likely to become obese 5 to 14 years later.

Mr. Whitener: One of the findings that really stood out for me and was kind of curious was that the prevalence of obesity was highest among children in the next-to-poorest socioeconomic group of the children that you studied. Do you have any idea as to why that might be the case?

Dr. Cunningham: Yes. So, this is something that was surprising to us also—that it wasn’t necessarily the children from the poorest households, but maybe children who were more toward the middle of the socioeconomic spectrum that tended to have the highest rates of obesity incidence during elementary and middle school. So, we didn’t actually look into the reasons why this might be the case.

The most striking difference, I think, was between those who were in the wealthiest families and everybody else. So, it’s almost like there is perhaps a protective component to being in a wealthier family, less than the disadvantage of living in the poorest household coming from these data, but overall I think what we took from this was that, really thinking about obesity, it’s important across the socioeconomic stratum. Everybody’s at risk.

Mr. Whitener: And we talked about this briefly earlier, but what did you find about when obesity starts to develop for children in the various groups?

Dr. Cunningham: So, we found that, and this is—so it was also quite surprising to us, actually, how early obesity seems to actually begin to emerge among kids looking at the prevalence of obesity; you sort of see it increasing across ages. It was surprising to us to see that a lot of it occurred actually fairly early on, so that by the age of 5, there were already elevated risks for some kids compared with others. So, in our study, at kindergarten entry about 12 percent of children were already obese.

Now, for most of our work we actually ignored those kids and focused on the kids who weren’t obese at kindergarten entry and followed them to see what the patterns of emergence of obesity were among them. And we found that the kids who were overweight seemed to have this elevated risk of becoming obese subsequently. And so it seems like something had been set in place already by the age of 5, which I think makes sense in light of a lot of the literature that suggests the importance of the first 5 years, the first 3 years of life, even the intrauterine environment.

The fact that we found that high birth weight was also associated with obesity suggested to us that some of these risks may actually be set in motion even earlier than age 5, and that perhaps even the intrauterine environment and intergenerational transmission of obesity risk may also be important in sort of perhaps elevating risk. But at the same time, we’re certainly not finding something that would suggest that “weight fate” or something like that for kids across the spectrum of weight early in life. Many of them went on to become obese, but many of them went on to be normal weight.

Mr. Whitener: I thought it was fascinating that kind of taking it from the other end of your measurement scale that almost 90 percent of obese eighth graders had been either overweight or obese in kindergarten, but only 13 percent of eighth graders who were normal weight had been overweight in kindergarten.

Dr. Cunningham: Yeah, yeah. I think what’s important from the applied perspective is that there is—this may give us some idea about which kids may benefit the most from focusing on healthy lifestyles and really promoting healthy weight. At the same time, a lot of the kids who were obese eighth graders had been normal weight in kindergarten, so it goes both ways.

Mr. Whitener: Right, and just to repeat what I said at the outset, you found that obesity was four times as high among children between 5 and 14 who were overweight before age 5, compared to children who had a normal weight at that age, so it’s really quite a dramatic finding.

Dr. Cunningham: Yes, so about 8 percent of normal weight kindergarteners went on to become obese by eighth grade, whereas about 30 percent of overweight kindergarteners went on to be obese by eighth grade.

Mr. Whitener: Now earlier you mentioned that understanding when the risk of obesity is greatest can help us in identifying potential ages where we can intervene and maybe make the greatest difference. What do these results suggest in that regard?

Dr. Cunningham: I think they help us focus on those very first years of life as being really important in terms of instilling healthy lifestyles and are important as a focus for interventions for parents. This is when we can really make a difference. There’s a lot of research that shows that little kids are really sort of shaping their preferences—what they like to eat, what they like to do—during the first couple of years, and they are looking around and seeing what their parents are doing, what their teachers are doing, and taking cues from that of what they’d like to do and what they’d like to have. And so, to me, I like to look at this optimistically, not as an issue of fate and “yikes, what we do now?” Once the kid is overweight that’s the end of it—certainly not—but actually thinking, wow, this gives us a really good place to focus and to start and to be optimistic about setting a healthy trajectory for kids’ entire lives.

Mr. Whitener: I think the results may also raise questions for some people about not only how early the path to obesity begins, but also the relative roles played by home environment, preschool environment, even biological factors and genetics. Did you find anything about that, or do you have any views on that?

Dr. Cunningham: Well, this is, unfortunately, it’s nothing I can really speak to quite yet. It is something that we’ve been thinking about, and that’s definitely come up as we’ve thought and talked about this paper with colleagues. I think the fact that there seems to be some importance in when you look at children’s birth weight, that we do find that that is associated with subsequent obesity risk. That tells us there’s something there that happens maybe even before we start talking about the first 5 years of life and the nurturing environments during those periods. And in large part, I think there’s been a lot of research that can give us some clues about the things that may be going on.

There’s a growing body of literature that’s focused on the intrauterine environment and fetal programming that basically suggests that what happens to you in utero really shapes how your body interacts with its environment for the rest of your life and isn’t so much focused exclusively on the genes, but basically the idea that genes sort of are told what will be beneficial, how they should express themselves during that intrauterine period. And we know that kids whose mothers are obese or whose mothers had diabetes while they were in utero are more likely to have higher risks of becoming obese, of developing diabetes. So, there’s certainly something about the intrauterine environment that’s important and that I think a lot of researchers are making important gains in this area. In terms of parsing genes from the environment, I think it’s hard, and I think increasingly we’re finding that they are intertwined in ways in which neither one nor the other can be exclusively important, but that there’s an interaction there.

Mr. Whitener: Great. We’ll stay tuned for more research on kind of teasing apart those differences, and in the meantime, this has been a terrific addition to our knowledge, and we look forward to seeing where your research goes from here.

Dr. Cunningham: Thanks very much. I really enjoyed talking with you, and I’ll keep you posted.

Mr. Whitener: We’ve been speaking with Dr. Solveig Cunningham, who is assistant professor in the Hubert Department of Global Health at Emory University.

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About the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD): The NICHD sponsors research on development, before and after birth; maternal, child, and family health; reproductive biology and population issues; and medical rehabilitation. For more information, visit the Institute’s website at http://www.nichd.nih.gov/.