Oddo Vanessa M, Jones-Smith Jessica C
From the Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD.
Am J Clin Nutr. 2015 Jun;101(6):1225-31. doi: 10.3945/ajcn.114.096693. Epub 2015 Apr 15.
Evidence suggests that changes in family income are an important determinant of children's body mass index (BMI). However, few studies have leveraged longitudinal data to investigate the association of changes in family income on changes in BMI z score.
This study aimed to assess whether gains in family income are associated with changes in BMI z score among children in the United States by using the nationally representative Early Childhood Longitudinal Survey Birth Cohort (ECLS-B).
We used longitudinal data from the ECLS-B to assess whether gains in family income, assessed by using the poverty to income ratio (PIR), were associated with changes in BMI z score among children aged 2-6 y. Child anthropometric characteristics and family income were assessed at 2-y, 4-y, 5-y, and 6-y visits. Sex-stratified, individual fixed-effects linear regression models compared children with themselves over time to control for time-invariant measured and unmeasured confounding factors. Models also controlled for time-varying confounders, including number of siblings, household structure (2 parents, one parent, or unrelated guardian), age, and age squared.
Children (n = ~9200) had a mean ± SE change in BMI z score of 0.12 ± 0.022, and family income increased by ~$3361 ± $536 during the 4-y period of observation (2003-2007). The association between increased PIR and change in BMI z score varied by sex but not by race-ethnicity. Among girls, an increase in PIR was associated with a statistically significant decrease in BMI z score (βPIR = -0.022; 95% CI: -0.042, -0.0016). There was a statistically significant association between PIR and BMI z score among preterm boys (βPIR + β PIRXpreterm = -0.067; 95% CI: -0.12, -0.018), but the relation was not statistically significant among boys born at term (βPIR = -0.0049; 95% CI: -0.024, 0.014).
By comparing children with themselves over time, we overcome many barriers that typically impede causal inference in observational studies. In this way, our study provides stronger evidence that gains in income during early childhood may promote healthy weight outcomes among girls.
有证据表明家庭收入变化是儿童体重指数（BMI）的一个重要决定因素。然而，很少有研究利用纵向数据来调查家庭收入变化与BMI z评分变化之间的关联。
本研究旨在通过使用具有全国代表性的儿童早期纵向调查出生队列（ECLS-B）来评估美国儿童家庭收入增加是否与BMI z评分变化相关。
我们使用ECLS-B的纵向数据来评估以贫困收入比（PIR）评估的家庭收入增加是否与2至6岁儿童的BMI z评分变化相关。在儿童2岁、4岁、5岁和6岁访视时评估其人体测量特征和家庭收入。按性别分层的个体固定效应线性回归模型对儿童自身随时间的情况进行比较，以控制随时间不变的已测量和未测量的混杂因素。模型还控制了随时间变化的混杂因素，包括兄弟姐妹数量、家庭结构（父母双方、单亲或非亲属监护人）、年龄和年龄平方。
在观察的4年期间（2003 - 2007年），约9200名儿童的BMI z评分平均变化为0.12±0.022，家庭收入增加了约3361美元±536美元。PIR增加与BMI z评分变化之间的关联因性别而异，但不因种族/民族而异。在女孩中，PIR增加与BMI z评分在统计学上显著降低相关（βPIR = -0.022；95% CI：-0.042，-0.0016）。早产男孩的PIR与BMI z评分之间存在统计学上的显著关联（βPIR +βPIRX早产 = -0.067；95% CI：-0.12，-0.018），但足月儿男孩之间的这种关系在统计学上不显著（βPIR = -0.0049；95% CI：-0.024，0.014）。
通过对儿童自身随时间的情况进行比较，我们克服了许多通常阻碍观察性研究中因果推断的障碍。通过这种方式，我们的研究提供了更强有力的证据，表明幼儿期收入增加可能促进女孩的健康体重结果。
