Dietary Intervention Combined With Exercise Improves Vascular Dysfunction but Also Obstructive Sleep Apnea in Obese Children
To the Editor:
We write in response to the article “Effects of Diet and Exercise on Obesity-Related Vascular Dysfunction in Children” by Woo et al.1 We agree with the conclusion of Woo et al that diet and exercise should be regarded as an important strategy to reduce the risk of arterial dysfunction in obese children. However, we believe Woo et al overlooked the important issue of obstructive sleep apnea syndrome (OSAS) in obese children.
Woo et al used a prospectively defined value based on US reference data, ie, body mass index (BMI) >23, to define obesity. A fixed BMI value should not be used in children for defining obesity because the normal range of BMI varies with age and gender. Moreover, data from the United States cannot be used as an international reference.2 For Hong Kong, local data are available, and the value for obesity is the 97th percentile of BMI.3
OSAS affected 13% to 36% of obese children.2 Nieto et al4 and Ip et al5 found that OSAS is a potent risk factor of endothelial dysfunction as measured by flow-mediated vasodilatation. Hence, OSAS represented an important confounding factor that was completely ignored in the study by Woo et al. Exclusion of known medical diseases will not exclude OSAS, which is usually asymptomatic in children. The “gold standard” for screening of OSAS in children is sleep polysomnography. Nonetheless, habitual snoring and observed apnea were shown to be important symptoms of OSAS. To exclude the effect of OSAS, Woo et al should at least exclude those with these two symptoms. We believe that a considerable portion of obese children enrolled in the study by Woo et al had undiagnosed OSAS. We suspect that the mechanism of reversibility of obesity-related vascular dysfunction discovered in their study was favorably affected by the improvement of OSAS, as previous studies have shown that weight reduction alone can reverse OSAS.
To the Editor:
The striking feature of the article by Woo et al1 is not so much that obesity-related vascular dysfunction in children is reversible with diet ± exercise but that these children are all Chinese. Chinese used to be known for their slender build.2 As a matter of fact, one rarely encountered an overweight person in old China.2 Now obesity has become an epidemic in China, among both adults2 and children.2,3
The lack of obesity in China in the past used to be attributed to ethnic background and genetic predisposition. The findings of Woo et al1 certainly dispel this misconception. Obesity, like atherosclerosis, is an acquired disorder. That atherosclerosis results from westernization of lifestyle has been amply demonstrated in the Japanese4 as well as Chinese5 populations. As my mentors, I. Snapper and W. Dock, used to say, if you live and eat like an American, you die like an American.
To the Editor:
We thank Drs Ng et al and Cheng for their interest in our work1 and their comments. We, too, are alarmed at the striking increases in obesity in childhood in China and indeed throughout many countries in the developing world.
We agree that the definition of obesity has been rather arbitrary, particularly in children. Nevertheless, what we have demonstrated is that some degree of relative obesity, whether overweight or gross obesity in children, is associated with arterial endothelial dysfunction and intima-media thickening, both as markers of early atherosclerosis as compared with lean children.2 We acknowledge that undiagnosed obstructive sleep apnea (OSA) may have been present in some children, but overnight polysomnography was regarded as impractical in this community-based sample of children. However, we consider OSA highly unlikely to have been an important confounder in our study. Our data showed near complete normalization of vascular function with sustained exercise, even though there was no significant overall change in body mass index. This argues (1) that exercise is important in restoring vascular function, even if obesity is not cured, and (2) that exercise is an effective intervention, regardless of OSA status.
We therefore regard exercise as almost certainly a much more practical solution than nocturnal continuous positive airway pressure, a therapy not well accepted or complied with in the pediatric population.