There is substantial evidence that early growth retardation, indicated by stunting, is associated with poorer cognitive function among children. There are, however, contradictory findings on the extent to which subsequent 'catch-up' growth among stunted children is associated with similar 'catch-up' cognitive functioning. In this paper we show that the apparent contradictions in the literature may be a result of differences in the definition of catch up used in the different studies. We explore two variations in definition: the age from which catch-up growth is measured, and the extent of growth required to be classified as 'caught up'. Using cohort data from South Africa with repeated measures of length in early childhood, we first show that varying the starting age from which catch up is measured from 1y to 2y greatly affects the conclusions drawn with respect to cognitive outcomes, as the prevalence of stunting tends to peak around 2y. Second, we show how the results differ when we vary what counts as catch up, and here we explore five definitions ranging from most lenient to strictest. The strictest definition requires children to have caught up sufficiently that their height-for-age falls within the 'normal' range at follow-up; very few children catch up to this extent. For all definitions of catch-up, except the strictest, we find that children who are stunted at 2 years of age who subsequently experience catch-up growth, on average, do worse on cognitive tests than children who were never stunted, and almost as poorly as children who remain stunted (with the coefficient ranging from -1.584; p < 0.01 to -1.753; p < 0.01). This suggests the timing of investments in early childhood is key, with intervention in the first two years to prevent deprivation that affects both linear growth and cognitive function.

中文翻译：

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身高和认知功能的追赶性增长：为什么定义很重要。

有大量证据表明，发育迟缓表明早期发育迟缓与儿童的认知功能较弱有关。然而，在发育不良儿童中随后的“追赶”成长与类似的“追赶”认知功能相关的程度方面存在矛盾的发现。在本文中，我们表明，文献中明显的矛盾可能是由于不同研究中所采用的追赶定义不同而导致的。我们在定义上探讨了两个变体：测量追赶性增长的年龄，以及需要归类为“追赶性”的增长程度。利用来自南非的同类群组数据并反复测量儿童早期的身长，我们首先表明，从1y到2y的变化开始追赶的起始年龄的变化极大地影响了关于认知结局的结论，因为发育迟缓的发生率倾向于在2y左右达到峰值。其次，我们展示了当我们改变追赶数量时结果如何不同，这里我们探索从最宽容到最严格的五个定义。最严格的定义是要求儿童在跟进时已充分追赶到年龄，使其年龄落在“正常”范围内。很少有孩子赶上这一程度。对于所有关于追赶的定义，除了最严格的定义外，我们发现在2岁以下发育迟缓的儿童平均而言在认知测验中的表现要比从未发育迟缓的儿童差，几乎和发育不良的儿童一样差（系数范围为-1.584； p <0.01至-1.753； p <0.01）。这表明在儿童早期进行投资的时机很关键，在头两年要进行干预，以防止剥夺同时影响线性增长和认知功能的行为。