The past 150 years have seen a massive improvement in the health of populations in Europe and North America. People live longer, eat larger quantities of more nutritious food, get sick less often and have better access to healthcare and medical technology. These general improvements have led to a large increase in the average height of the population: 11 cm in Britain. This large increase in height made me wonder a couple of years ago whether and how children’s growth has changed over time as well. This blog post explains what we currently know about the differences between child growth today and in the past, and why it is important to study changes in children’s growth over time.
So what defines children’s growth? Children do not grow at a constant rate. They grow fastest in the first four or five years of life, and during their pubertal growth spurt, which occurs between ages 8 and 12 for girls and ages 11 and 15 for boys in modern, healthy populations. Figure 1 presents an idealized view of the speed at which children should grow based on the World Health Organization (WHO) standards. The speed at which a child grows, the length of his/her growing years, and the timing of his/her pubertal growth spurt all contribute to give each child a unique growth pattern. Thus, Figure 1 is the average growth pattern for healthy children today.
Figure 1: Growth velocity of boys and girls at different ages according the WHO standards.
However, this modern, healthy growth pattern is very different from the growth pattern that we observe for European and North American children in the past. You might expect that if British adults in the mid-nineteenth century were 11 cm shorter, then children would just grow at a slower rate across all ages but maintain a similar timing of the pubertal growth spurt and length of the growing period. Yet this is not the case. Children’s growth in the past was different in three ways:
- Children often grew at slower rates
- They grew for a much longer period of time than children today, finishing their growing period in their early twenties rather than late teens
- They also had a delayed pubertal growth spurt that was several years after their modern counterparts.
This historical growth pattern for European and North American children is similar to the growth pattern observed in developing countries today. Figure 2 shows the growth pattern for three populations of boys in North America in the late nineteenth century. You can see that each has slower growth before the age of 10, a delayed pubertal growth spurt and faster growth in the late teen than the WHO standard. This pattern is similar to British children in the same period. Thus, there has been a change in the growth pattern of children over the past 150 years.
Figure 2: Growth velocity of boys in the late nineteenth century compared to the WHO standards.
So why should we care about changes in the growth pattern? Understanding how child growth has changed and what policies and interventions contributed to these changes will not only improve our knowledge of health in the past but also contribute to current policy discussions. Stunting rates (the percentage of children who are short for their age) are commonly used as an indicator for malnutrition in the developing world. Thus, a long-run historical perspective will help us understand the long-run impacts of policies and interventions on stunting and the reasonable level of improvement in stunting that we can expect when setting development goals.