Lancet 2020; 396: 151124. doi: 10.1016/S0140-6736(20)31859-6
This study aimed to estimate trends in mean height and mean body-mass index (BMI) between 1985 to 2019 for children and adolescents aged 519 years There was a difference of ≥ 20 cm in mean height and of 910 kg/m2 in mean BMI in 19-year-old adolescents between countries with the tallest/largest populations and the shortest/leanest populations The heterogeneity of trajectories between populations suggests variable nutritional quality and lifelong health benefits and risks
This study contrasts with most of the literature which focuses on the first five years of life and on the preconception period. It is important to remember that genetics plays a relatively small role in growth in height and BMI during the first 5 years of life. Indeed, the WHO Multicentre Growth Reference Study (1997 to 2003) that led to the design of the 0-5 years WHO growth charts demonstrated that under optimal social and nutritional conditions during preconception, pregnancy and the first 5 years of life, the variability in height and BMI between the six participating countries (Brazil, Ghana, India, Norway, Oman and USA) is minimal. A major limitation of the present study is that the causes underlying the observed heterogeneity in height and BMI changes between 5 and 19 years over several decades across most of the worlds countries remains unclear. This knowledge will be necessary to optimize public health programs in particular in countries that are affected by the unhealthiest changes. Specifically, understanding the differences between countries, such as Vietnam, Azerbaijan (girls) or Montenegro (boys) where height increased proportionally more than BMI (changes perceived as healthy) and most countries of sub-Saharan Africa where BMI increased proportionally more than height (changes perceived as unhealthy), could inform public health policies. The respective roles of events that occurred in early life and between 5 and 19 years are also unclear. It is suggested that any changes in public health practices that may derive from the present data should not be limited to changes in children and adolescents aged 5 and 19 years but should also include early life experiences.