Published: 17th July 2020
Stunted for life? Catch-up growth and the debate on reversing stunting
Stunting is widely acknowledged as a major public health problem. In 2012, over 162 million children under the age of five were stunted – about 25% worldwide. In this context, the World Health Assembly set up the ambitious target to reduce the number of children that are stunted by 40% by 2025. However, the goal is far from being met: in 2019, 144 million children were still stunted. Against the backdrop of the current COVID-19 pandemic, it becomes more and more unlikely that the 2025 goal will be reached as it appears numbers are on the rise again. Nevertheless, the question remains: how do you go about achieving such a goal in the first place?
There are two conceivable strategies for reducing stunting, namely, to prevent stunting before children are affected and to provide some form of cure for already stunted children. Global efforts have mainly been focused on the former approach. While the factors that cause stunting can be modified to prevent it, once stunting has occurred, it is considered irreversible, and a ‘cure’ in the conventional sense does not exist. Stunting is not some form of temporary illness but the long-term outcome of the suboptimal development of a child, both physically and cognitively. But is the outlook for stunted children really always so gloomy?
Catch-up growth: can we reverse stunting?
Not quite. Recent research has observed a seemingly contradicting phenomenon, called catch-up growth. This happens when children who were initially considered stunted according to the World Health Organisation’s height-for-age z-score (HAZ), later experience sudden spurts of growth, which some academics have interpreted as a form of recovery. Several studies have found the manifestation of catch-up growth to correlate with factors such as carotenoid-intake and gender, consumption of a micronutrient-fortified supplement, the mother’s height, age and parity, as well as birth weight and household socioeconomic status.
A new study authored by Subhasish Das et al. explored the role of water, sanitation and hygiene (WASH) practices on recovery from stunting. It also looks at reversal of stunting at different ages. The study focused on 612 children under the age of two from seven countries across three continents. Although WASH practices are instrumental to the prevention of undernutrition, being closely linked to the prevalence of infections, gut health and absorption of nutrients, the study could not find any significant effect of WASH on the reversal of stunting.
Instead, it showed a strong statistical indication that children stunted at an older age had higher chances of recovery:
“In comparison with children who were stunted at 6 months, children who were stunted at 12 months had 1.9 times […] more chances of recovery at 24 months of age. And, children who were stunted at 18 months of age had even higher odds […] of recovery […]”.
As an explanation for this finding, researchers suggested that catch-up growth requires support from the child’s immune system and that the immune competence of children, in turn, increases with time. Overall, the study proposes that programmes to promote linear growth should be directed at the earliest possible stages in development.
The debate: relative and absolute catch-up growth
Yet, none of the above-mentioned conclusions are unequivocal since research outcomes can vary greatly depending on which definition of catch-up growth was applied in the study. Some consider catch-up growth as the decrease of the deficit between the individual and the healthy population reference (absolute), while others define this as a relative change. Although this appears to be only a minor technical distinction, it makes all the difference in the context of statistics. Often factors showing a significant statistical association regarding the recovery from stunting using the relative definition will prove to have no considerable impact if the absolute definition is adopted.
When using the relative definition, we define catch-up growth when the child’s height converges toward the average height of healthy children of the same age. “This may or may not mean that their height caught up in absolute cm terms, however”. When using the absolute definition we consider the decrease in the height difference between the subject and the healthy population. Hence, we have catch-up growth when the height-for-age difference declines. Since the average height of a healthy child increases more slowly at older age, it is possible that the height of a child improves in relative terms while the absolute deficit from the healthy reference population remains. This means that relative catch-up growth does not necessarily coincide with proportional absolute growth, which some therefore consider to be the only accurate definition.
In light of this, the scientific debate about whether catch-up growth is possible or whether linear growth retardation incurred in early childhood is irreversible continues. This is additionally complicated by the underlying fundamental question of whether the inducement of catch-up growth is sufficient to reverse the damage that undernourishment has already caused. Indeed, ongoing efforts focused on preventing stunting remain critically important. All in all, there is a consensus among scholars that further research must be done in this area if it is to be used effectively in the fight against stunting.
‘Catch-up growth in child stunting has always been a contentious issue, but it’s exciting that there is now interdisciplinary interest in unpacking the complexity of this issue‘
Prof Claire Heffernan, Principal Investigator
Written by Julie Manseck, Communications Intern
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