Obesity in childhood, ambulatory blood pressure and lifestyle interventions

During the past decade, the number of studies addressing the issue of hypertension in childhood and its tight relationship with overweight has grown exponentially [1,2]. Conclusive evidence has also been provided on the existence of a strong association between blood pressure values and visceral fat amount not only in adults, but also in children as well [3–4]. Whereas on the one hand, literature is so overwhelming in providing descriptive images of this important problem, on the other hand, it seems to be quite reticent in proposing solutions and in documenting that therapeutic interventions in children aimed at reducing overweight are successful also in exerting other positive cardiovascular effects such as, for example, in reducing elevated blood pressure values. In this target group, data regarding the effectiveness of nonpharmacological interventions based on lifestyle modifications are particularly lacking. A recent meta-analysis reports that from 1975 until today, 33 studies correctly evaluating the effectiveness of lifestyle interventions in obese children have been published and that surprisingly only in seven of them, the effects of body weight changes on blood pressure values were taken into account [5]. Furthermore, only one randomized study shows the ability of exercise physical training in reducing elevated blood pressure values in obese hypertensive children [6]. Future studies will be thus needed to fill this gap of information, taking also into account that guidelines on hypertension in children and adolescents indicate in the increase in physical activity, in the reduction of the sedentary lifestyle, as well as in the adoption of correct food habits, the first-line interventions to be adopted in this high-risk young population [7]. In the present issue of the Journal, Hvidt et al.[8] report the results of an interesting study aimed at defining the 1-year effects of a structured tailored lifestyle intervention based on dietary caloric restriction combined with a physical exercise program on body weight as well as on clinic and 24-h ambulatory blood pressure in obese children. One year of nonpharmacological treatment induced in about three-quarters of the recruited patients results in a significant reduction in BMI, waist/height ratio and body fat percentage, as assessed by the high-sensitive dual-energy X-ray absorptiometry scanning technique. The decrease in anthropometric variables was closely related to the reduction in ambulatory (but not in clinic) blood pressure values, expressed as ‘z scores’, to correct them for a number of confounders including sex, age and weight. The results of the present study deserve to be discussed taking into account a number of considerations. First, whereas in adults, ambulatory blood pressure monitoring is a procedure largely adopted in clinical practice for a correct diagnosis of hypertension and for assessing the ability of a given therapeutic intervention to exert blood pressure-lowering effects [9], in children, its usefulness is much less documented. Second, the reference values indicated by the pediatric recommendations for defining the normality values of ambulatory blood pressure [10] are based on a single study performed in a relatively small group of children (less than 1000) belonging to a single ethnic group [11]. This is in sharp contrast with what occurs for the ambulatory blood pressure reference values in the adult population, which are derived on data collected in a consistent number of studies, performed with the aim at defining this crucial methodological aspect of the problem [9]. The two above-mentioned considerations explain why the gold standard for the diagnosis of hypertension in children still remains sphygmomanometric blood pressure, whose values have to be taken into account, considering the age, height and sex-specific percentiles [7]. The most recent and updated pediatric recommendations suggest the use of ambulatory blood pressure monitoring in some specific clinical conditions, such as in white-coat hypertension, masked hypertension, in high-risk young populations (such as in hypertensive patients complicated by renal dysfunction or target organ damage) or when the effectiveness of therapeutic interventions need to be directly monitored [10,12,13]. However, a study recently published carried out in a large population of children has cast some doubts on the usefulness of ambulatory blood pressure monitoring technique for the diagnosis of white-coat and masked hypertension in patients younger than 10 years of age [14]. This is because in this category of children, ambulatory blood pressure values are higher than the office ones, as shown years ago in normotensive children [15]. On the contrary, in untreated hypertensive children and adolescents, office blood pressure values have been shown to be higher than the ambulatory ones similarly to what is generally observed in normotensive adults [14]. The study by Hvidt et al.[8] has been performed in a sample of patients with a mean age of 12 years, presenting with severe obesity, in whom ambulatory blood pressure monitoring was not used for diagnosing hypertension, but for evaluating the effect of body weight-reducing interventions on the blood pressure values. The results obtained suggest that in this particular population, in which probably the number of patients with sympathetic hyper-reactivity and true white-coat hypertension is by no means negligible, ambulatory blood pressure monitoring may allow to achieve more complete and valid information than office blood pressure, especially when patients are examined before and following a therapeutic intervention in order to assess its effectiveness in clinical practice. Taken together, these findings provide evidence on the importance of ambulatory blood pressure monitoring approach in the diagnosis of pediatric hypertension. They also emphasize that, similarly to what has been described in adult hypertensive patients [16], also in very young patients with high blood pressure, sympathetic activation is a factor of major pathophysiological relevance [17]. In this context, however, it should be emphasized that, at variance, from what it has been reported in adults [18], in the children enrolled in the present study, body weight reduction did not trigger any heart rate decrease [8]. Whether this finding should be taken as an evidence against the sympatho-moderating effects of body weight reduction in young patients remain to be seen, also considering the well known limitations of heart rate as an adrenergic marker [19]. Finally, it is also important to underline that longitudinal follow-up studies in children are few and, more importantly, extremely difficult to be realized. Children grow, and body weight, waist circumference and blood pressure values increase in a physiological manner. For this reason, it is necessary that data deriving from prospective studies in pediatric populations are analyzed in an extremely rigorous manner, taking into account the effects of ageing ‘per se’ on the different parameters. The study by Hvidt et al.[8], even if performed in a limited number of patients, gives a good example of a correct fulfilment of this type of analysis. As already mentioned, blood pressure and BMI values were transformed in ‘z-scores’ and waist circumference was adjusted for height, thus allowing a proper comparison between baseline and follow-up data. The study findings are strengthened by the evidence that the observed reductions in ‘z-scores’ for BMI and waist/height ratio are confirmed and validated by the consensual changes in total body fat percentage, quantified by the method of dual-energy X-ray absorptiometry [20]. In conclusion, the results of the study by Hdivt et al.[8] underline the potential value of ambulatory blood pressure monitoring for the assessment of the effectiveness of nonpharmacological interventions in a population of children and adolescents with considerable overweight. Further studies are, however, warranted to better characterize several features of the approach that still remain unaddressed. ACKNOWLEDGEMENTS Conflicts of interest There are no conflicts of interest.