The main characteristics and results of the 14 studies in children, published between 2006 and 2013, are shown in Table 3. Twelve studies were cross-sectional and two32,33 were cohort studies. Nine of them were conducted in Europe,19,32,34–40 three in America (one in Brazil41 and two in Mexico33,42), and one in Asia.43 One other study44 was an international study conducted in 20 countries. All studies examined both boys and girls with sample sizes ranging from 158 (cohort) to 50,004 (cross-sectional).