Childhood obesity, autonomic cardiovascular regulation and regular physical activity
- 1Istituto di Ricovero e Cura a Carattere Scientifico San Raffaele Pisana, Roma, Italy
- 2Dipartimento Medicina dei Sistemi, Università Tor Vergata, Roma, Italy
- Correspondence to Dr Ferdinando Iellamo, Dipartimento Medicina dei Sistemi, Università Tor Vergata, via Montpelier 1, Roma 00173, Italy;
- Received 8 November 2012
- Accepted 13 November 2012
- Published Online First 4 December 2012
The current epidemic of childhood obesity is a major public health concern. Early obesity strongly predicts later cardiovascular disease, and excess weight may explain the dramatic increase in type 2 diabetes, a major risk factor for cardiovascular disease. Based on the 2007–2008 National Health and Nutrition Examination Survey data, a report by Ogden et al1 indicates that almost 17% of school-aged children and adolescents are obese, defined as body mass index (BMI) for age at or above the previously established 95th centile. Similar trends have been observed in Europe. In Italy, a large survey study, performed in about 46 000 children aged 6–11 years, indicated that 23% are overweight and 11% obese.2 Childhood obesity strongly relates to early atherosclerosis and obesity-related cardiovascular disease. In children and adolescents, BMI is strongly related to high blood pressure (BP),3 and the prevalence of hypertension ranges from 47% to 62% in obese paediatric patients.4 ,5 The appearance of paediatric forms of chronic diseases such type 2 diabetes, metabolic syndrome and hypertension contributes to increased risks in adult life6. If the increase in obesity were to continue on the same track, researchers have predicted that, by 2020, almost half of US adults would meet the World Health Organization criteria for obesity.7 Excess weight also carries an economic burden. The Centres for Disease Control and Prevention have estimated a medical cost for obesity-related conditions of 10% of total annual US medical expenses in 2008, or US$147 billion.8 In addition, obesity, hypertension and glucose intolerance in childhood have been recently reported to be strongly associated with increased rates of premature death in adulthood—that is, death before 55 years of age.9
There is now compelling evidence that regular, moderate to vigorous, physical activity effectively counteracts childhood obesity. Recently, the US preventive Service Task Force after reviewing clinical studies on obese children, reported that short-term (up to 12 months) comprehensive interventions that included physical activity, dietary and behavioural counselling components were effective in improving BMI in obese children.10
Several factors, interacting with each other, are believed to contribute to the increased cardiovascular and metabolic risk of obese individuals, of which, alterations in regulation of the autonomic nervous system play an important role. Reduced cardiac vagal activity accompanied by enhanced sympathetic vascular activation has been reported in overweight/obese children.11–13 Lucini et al14 report that children who remain obese despite practising vigorous, organised and supervised physical activity still feature reduced baroreflex gain with enhanced low frequency power of arterial pressure variability and higher BP compared with normal-weight peers performing the same training schedule. These interesting findings prompt the following considerations. On the one hand, the study confirms that obesity is characterised by increased peripheral sympathetic activation and reduced cardiac vagal modulation, possibly leading to arterial hypertension, from an early age. On the other hand, these findings apparently contradict, in part, the assumption that regular exercise training prevents/reduces weight gain, improves baroreflex control of the heart rate, and decreases sympathetic activity. Although a wide range of genetic, biological and environmental factors contribute to the development of obesity,15 energy imbalance resulting from limited physical activity and excess energy intake is considered the most important, and modifiable, factor. The study by Lucini et al14 highlights the fact that exercise alone may not be able to prevent or treat obesity in children. This requires more complex interventions in dietary habits and sedentary lifestyle. Increasing findings indicate that children are especially vulnerable to unhealthy food and sedentary habits, independently of concomitant regular physical activity. Some reports suggest that higher levels of objectively measured time spent sedentary (eg, TV viewing) are associated with adiposity16 and an adverse cardiometabolic risk profile.17 These factors may have affected the results of Lucini et al14 since they were obtained through questionnaires and self-reports. Questionnaires are unsatisfactory indexes of physical activity actually performed, particularly in a young population.
The cross-sectional nature of the study, with its inherent limitations because of some uncontrollable bias such as non-training-related differences between groups and interindividual variability, may also have affected the results. Indeed, some studies have shown that physical activity programmes produce significant changes in cardiac parasympathetic activity in children,18 and even a short-term regular physical activity programme has been reported to reduce BP in a small cohort of prepubertal obese children.19 Moreover, it should also be considered that, at the age of 11 years, even if coaches instruct children to perform the same training activities during exercise sessions, those who are already overweight often tend to self-limit their physical effort.
This proof-of-concept study has the merit of having evaluated some measures of health status with potential pathophysiological implications, in this case autonomic nervous system control parameters, which also need to be assessed, in addition to weight-related parameters, in a mechanistic perspective. In this context, spectral analysis of heart rate variability could be ideal for evaluating the autonomic mechanisms sustaining obesity-related complications, in large-scale paediatric research with sustainable costs. Indeed, it has been shown that heart rate variability can be used to track physical activity-induced changes in autonomic regulation.20
The effects of physical activity on weight and systemic BP, with its underlying mechanisms, in children are still to be confirmed in large cohorts, since most data on physical activity rely on small sample sized, short-term, longitudinal studies, and the report by Lucini et al14 might provide a basis for designing more robust investigations on the beneficial effects of sport activities as a lifestyle treatment for obesity and related cardiovascular autonomic dysregulation. The volume, intensity and duration of physical activity needed to improve/prevent overweight/obesity and metabolic and autonomic (dys)regulation is still to be firmly established. Two main problems with the use of physical activity in the prevention of overweight/obesity-linked risk are: (1) the dose of physical activity that is associated with overweight prevention and treatment and (2) the relative lack of objective measures of the dose of physical activity with related total energy expenditure (TEE), which is fundamental for overweight prevention/weight loss programmes.
The levels of physical activity required in youth have been developed mainly from studies on self-reported activity by questionnaires, which lack the possibility to measure the actual amount of physical activity performed, the crucial factor in TEE. During the past decade, technology that provides objective assessment of the amount of physical activity has increased, especially through motion sensors. A better understanding of the relations between physical activity and sedentary time in relation to cardiometabolic risk factors will aid the development of physical activity interventions, counselling and public health policy.
In this context, schools represent a unique environment for community intervention/prevention strategies, because children spend more time in school than in any other setting, and there is the possibility to interact with parents and teachers. School-based learning activities may also provide a knowledge base and rationale for changes in physical activity and dietary habits of children.
Implementation of exercise and other long-term lifestyle-changing programmes especially designed for children aimed at preventing/treating obesity and related health problems should be adopted with the support of public health organisations.
Contributors Both authors read the original article for which this editorial has been invited and discussed the content of the editorial.
Competing interests None.
Provenance and peer review Commissioned; internally peer reviewed.