Discussion
In this study, we evaluated the weight status of children with CHD compared with a large, population-based control group, using data on weight and height collected at preventive health checks offered to all Danish children. Underweight was more prevalent in the CHD population than in the general population. This was most pronounced for individuals with severe CHD including those with UVH but was also observed for individuals with mild CHD. However, among those who were underweight at 1 year of age, with later BMI recordings between ages 2 and 5 years, the prevalence of underweight decreased substantially, suggesting that early underweight status may be largely temporary in both CHD subjects and population controls. The prevalence of obesity among children with CHD was not increased compared with the general population or compared with international normative data. This was true for all the defined categories of CHD severity and in the presence of preterm birth or ECDs.
Our data are in line with and extend the reports on BMI data identified in hospital settings. Studies from USA, Canada and Turkey have reported prevalence estimates of obesity in patients with CHD that were similar to that of controls referred to hospital clinics or compared with normative national data.9–11 15 A Taiwanese study from 2012 including data from a school survey, performed both in first grade and senior year of high school, also reported a similar prevalence of obesity among individuals with CHD and control subjects.16 Underweight, as defined in their study as BMI <15th percentile, was more prevalent in the subjects with CHD, which is consistent with our finding, although the definition of underweight is different. We observed an increased risk of being underweight across all types of CHD. Similarly, a US study from 2013 reported an increased prevalence of failure to thrive in CHD individuals with biventricular heart disease without the need for repair.4 As the authors suggested this may partly be attributed to individuals with VSD, which may be haemodynamically significant early in life even if they later self-resolve. Similar mechanisms may potentially pertain to underweight.
With the worldwide increase in obesity, there is still a need for cardiologists and practitioners to address the subject, even though the prevalence of obesity in children with CHD did not differ from the control groups. The fact that obesity rates in the CHD population do not exceed those of the general population does not mean that obesity should be ignored as a risk factor. Obesity remains evident in the CHD community, simply at rates comparable to the general population. In fact, the risk of obesity in those with CHD may be of greater consequence since obesity increases the risk of complications like diabetes mellitus, coronary artery disease and heart failure.26 27 Of note, since the relationship between BMI and cardiometabolic risks is complex, and considering that there are inherent limitations of BMI measurements, such as the inability to differentiate between body fat and lean mass, caution should be applied when interpreting our results.
Study strengths and limitations
Prospective information on height, weight and BMI was obtained via annual preventive health checks offered to all Danish children. As data were only available on 30% of the population, this does raise the concern for selection bias. However, when we compared our study subjects with the larger available cohorts for both the CHD and the general population groups, the characteristics of the group did not substantially vary according to availability of BMI data. Since these measures were only recently made compulsory, it seems unlikely on review of our data that those subjects with missing BMI data were missing for reasons that predisposed them to abnormal BMI.
The group of subjects with CHD was identified through DNPR, and our results depend on the validity of these diagnoses. The positive predictive value of overall presence of CHD according to the DNRP is reported to be 89%.28 Using the previously described exclusion criteria, the positive predictive value will likely be even higher.19 Despite a relatively large study population overall, the precision of CHD severity-specific estimates, especially for more complex conditions, was low, leaving variation in HRs statistically insignificant. In addition, a larger study population would have allowed more clinically relevant analyses on subgroups with various types of ECDs.
We defined underweight as less than the fifth percentile and obesity as greater than the 95th percentile relative to BMI levels of children from the general population of the same age and sex. This enabled a comparison that was free from bias due to variation in BMI levels across countries. To further quantify the obesity prevalence in Danish children, we also presented the prevalence of obesity according to an international age-specific and sex-specific BMI standard.22 This indicated a relatively low prevalence of obesity in Danish children. However, this does not prevent generalisation of the comparisons of abnormal BMI prevalence estimates of children with and without CHD.