Childhood obesity has become an epidemic in the United States, with an estimated 31.7% meeting the definition of overweight or obese.3
The results of this study indicate that a substantial proportion of children with IBD, particularly UC or IC, are also either overweight or obese. This is important, as obesity may be associated with increased complications of disease and also with long-term cardiovascular and metabolic complications. In the adult IBD population, obesity has been associated with shorter time to development of perianal complications, more active disease, and more frequent hospitalizations.8
Furthermore, obesity-related comorbidities may indirectly affect IBD-related morbidity and mortality, as well as increase the potential for polypharmacy and medication interactions. The pathophysiology of obesity supports the association with increased severity of disease. Obesity can be considered a chronic low-grade state of inflammation. In obesity, adipose tissue can undergo a transformation and become infiltrated by macrophages.14
In addition, many pro-inflammatory markers linked to obesity and adipose tissue (including leptin, adiponectin, resistin and ghrelin) have also been linked to IBD.15, 16
These markers may become upregulated, contributing to disease activity.
The results of this study are consistent with the results of a previously published study of newly diagnosed (untreated) CD and UC from two separate North American cohorts initiated in 2000. Kugathasan et al
found that most children with CD or UC had a BMI percentile in the normative range. However, 10% of children with CD and 20-30% of children with UC were overweight or at risk for overweight (with new consensus definition, this would represent overweight or obese).10
In the present study of treated IBD, we found even greater rates of overweight and obesity. Similar to Kugathasan et al,
we also found higher rates of overweight and obesity among children with UC/IC as compared to CD, although CD patients still had a 20% prevalence of overweight or obesity.
Similar to adult IBD populations,8
the results of this study also indicate that pediatric patients with CD who are either overweight or obese have had higher rates of IBD related surgery. In UC/IC, this trend did not reach statistical significance. These pediatric data, in combination with prior adult data, suggest that obesity in IBD may be an independent predictor of a more complicated disease course.
The early literature on pediatric IBD found associations between weight and growth retardation and juvenile onset of IBD, especially CD. 9
Malnutrition is even a component of the most commonly used disease severity indices in CD, the Crohn's Disease Activity Index (CDAI) and the Pediatric Crohn's Disease Activity Index (PCDAI). Since the earliest descriptions of IBD, a greater number of medications have become available for treatment and both CD and UC may be recognized earlier in the course of the disease. For these reasons, malnourishment may no longer be a common manifestation of treated pediatric IBD. Rather, children with IBD may now be following the course of the rest of the population, with a greater percentage overweight or obese than ever before.
The factors we found to be associated with overweight and obesity, including non-Caucasian race and Medicaid insurance status (a proxy for lower socioeconomic status), have also been shown to be associated with overweight and obesity in the general pediatric population.3
We also found thiopurine use to be inversely associated with overweight and obesity in patients with CD. We speculate that current thiopurine use may be a marker for prior disease severity associated with malabsorption. Environmental factors such as excess energy consumption and decreased physical activity can exacerbate the tendency towards obesity in all children,4
regardless of chronic disease status. Appropriate lifestyle interventions for obesity, including dietary modifications and increased physical activity, are important for all overweight or obese children, including those with IBD.
Surprisingly, we found few associations between current medication use and overweight and obese status. Current prednisone use was not associated with overweight and obese status in CD, although a non-significant trend was observed in UC. Perhaps, this reflects the fact that prednisone use was reserved for the treatment of more severe disease, the population of patients which might have had the lowest BMI prior to corticosteroid initiation. Alternatively, it may only be prior use of corticosteroids that is associated with overweight and obese status, as the weight gain occurs over time. We did account for prior corticosteroid use in subanalyses (corticosteroid use at the time of enrollment or subsequent visit). We were unable to account for all prior corticosteroid use, as we only had information on current use at the time of visit. This may have contributed to the lack of association in patients with CD. We did find a significant increase in the prevalence of overweight and obesity in patients with UC/IC on prior or current corticosteroids. Of note, we also found a small and non-significant association between current infliximab use and overweight and obese status, an observation often noted in clinical practice.
There are several strengths to this multi-center study. We were able to study a large number of children with IBD, allowing for more precise estimates of BMI percentiles. The centers included in the Improve Care Now collaborative represent a mixture of private, not-for-profit, and academic centers of various sizes and from all regions of the United States, increasing the generalizability of these results. The database also contained extensive data on clinical disease characteristics, including duration of disease, phenotype, assessment of severity, and prescribed medications. Therefore, we were able to control for many potential confounders of the relationship between IBD and overweight and obese status.
There are several limitations to this study. The cross-sectional design of this analysis precludes definitive causal inferences regarding associations between BMI and specific disease characteristics or medication utilization. In addition, confirmation of clinical variables in the database, other than anthropometrics, was beyond the scope of this study. However, we did ask sites to confirm outlying height and weight measurements, and found these to be remarkably accurate with very few errors (<3%). Also, the proportion of overweight and obesity in any given population will vary according to where the continuous variable for BMI is dichotomized. We did perform additional analyses using BMI-percentile as a continuous variable and found similar results. A priori, we chose to use standard definitions of overweight and obesity consistent with the CDC BMI-for-age growth charts. Use of other standards might result in other proportions, but would be unlikely to significantly change the independent effects of demographic and disease characteristics seen in our model.
In summary, overweight and obesity are common in pediatric IBD. Little is still known about how childhood obesity will affect the adult outcomes of patients with IBD. The results of this study have important implications for the care of children with IBD. It is important for providers to recognize that CD and UC/IC can exist in overweight and obese patients, and that the traditional description of malnourishment in pediatric IBD may no longer represent the majority of cases. Because gastroenterologists have unique expertise in nutrition and improved access to dieticians and other multidisciplinary resources, screening, counseling, and treatment for overweight and obesity should be the standard of care for the patient with IBD. Lifestyle modifications, including dietary modification and physical activity, are important for all overweight and obese children, including those with IBD. Further studies on the relationship between obesity and inflammation in the pediatric population are warranted.