If you’ve read anything about obesity in the lay press over the past week, you already know that there has been a decline in the prevalence of obesity in American preschoolers. The CDC’s latest National Health and Nutrition Examination Survey (NHANES) data, published in the Feb. 26 issue of the Journal of the American Medical Association, show a significant decline in obesity among children aged 2 to 5 years. Obesity prevalence for this age group went from nearly 14 percent in 2003-2004 to just over 8 percent in 2011-2012. This information has been rippling throughout the press this week, with headlines like “U.S. Childhood Obesity Rates Fall 40% in Decade.”
For me, this news is both exhilarating and anxiety provoking. On one hand I have been working throughout that period alongside countless others to achieve a population decrease in body mass index (BMI) and the news that the day may have finally come for one segment of the pediatric population is incredibly encouraging. On the other hand, the rate is still 8.1 percent, as compared to 4.1 percent in the 1971-1974 NHANES cohort, and celebrating too early could distract from the fact that there is so much more work to be done, especially for our most vulnerable children.
The first question that crossed my mind when the news first landed in my inbox is whether the tide has really turned. Experts agree that the sampling methodologies in NHANES are robust and the data are valid. The pressing questions are (a) whether we are really seeing a trend and (b) whether that trend applies to the most vulnerable children.
There are two ways in which I think about data like this. The first is with a gut check—does this jive with what I see in my Community Health Center patients? Although I am not sure that my observation techniques are sensitive enough to see a change from 12 percent in the last cohort to 8 percent in this one, it does seem like recent changes in WIC, SNAP and childcare settings, among others, have made families in my clinic more aware of the impact of healthy eating and active living on the weight and health of their children. And when I saw an obese 2-year-old child this week, I actually thought to myself that I had not seen an obese preschooler in at least a few clinic sessions—certainly a change from five years ago. So is it possible that the tide has turned for preschoolers based on my clinical experience with an underserved urban population? I think so.
But I would be hard pressed to claim that my clinical experience is sufficient to validate public health trends. So I did what improvement junkies do. I went back to the numbers. The most recent data stratified by race and ethnicity has not yet been made available so I was only able to look for a trend among all preschoolers. I plotted the NHANES data from 1999 to 2012 using CDC data to determine if there really is a trend, creating a graph of obesity prevalence over time, what is known in quality improvement as a run chart.
A run chart is designed for the early detection signals of improvement over time through recognition of non-random patterns in the data. The first possible pattern is a “shift,” defined as six or more successive points that are all above or below the median, which in this case is 10.6 percent. If our recent changes in policy and practice had caused a shift beginning in 2005-2006, we would see that the next six points fall below the median. But in fact, the four points from the 2005 cohort to the 2011 cohort alternate between being above and below the median, indicating we don’t have enough data to see a shift and that we don’t appear to be on our way to one just yet. We can also look for a “trend,” defined as five or more consecutive points that are either ascending or descending. Similar to the case of the shift, we neither have enough data points, nor do we have indication that we are on our way to a trend. So despite the change in prevalence, it is challenging to use the data to either establish a new, lower baseline prevalence or to attribute the decrease to the changes we have made to the environments of preschoolers.
So where does that leave me? Trend or no trend, this news means thousands and thousands fewer preschoolers are obese in 2011-2012 vs. 2003-2004 and this fact will have an enormous impact on our health resources and outcomes as they mature. And these data give us hope that sustainable improvement could be just around the corner. In any case, we must continue to invest heavily in activities and policies that promote healthy weight to create a change in prevalence that will persist over time. If nothing else, this is a moment to pause, applaud all of the wonderful changes we have made to date, and energize ourselves for the long road ahead—to the day when we have reversed the trend for ALL Americans, regardless of age, race, or class.