Katagiri Aomi, Nawa Nobutoshi, Fujiwara Takeo
Department of Global Health Promotion, Tokyo Medical and Dental University, Tokyo, Japan.
Department of Medical Education Research and Development, Tokyo Medical and Dental University, Tokyo, Japan.
Front Pediatr. 2022 Jun 14;10:782940. doi: 10.3389/fped.2022.782940. eCollection 2022.
Prior studies have shown that children who are the only child are more likely to be overweight compared to their peers with siblings, regardless of whether they are the oldest, in the middle, or youngest. The study objective was to clarify whether there is an association between the length of the only-child period and the risk of overweight in firstborns who experienced an only-child period during early childhood before their siblings were born.
A total of 7,576 first-born boys and 7,229 first-born girls were examined from a nationwide longitudinal survey in Japan. The length of the only-child period was determined by "birth interval"; i.e., the interval between the birth of the index child and the birth of the second child. It was categorized as short (<1.5 years), moderate (between 1.5 and 4 years), long (between 4 and 8 years), and only-child (the second baby was not born for 8 years). Overweight was defined as body mass index (BMI) z-score 1 standard deviation or more at age 8. Logistic regression was used to examine the association between length of only-child period and childhood overweight, adjusting for covariates.
Moderate birth interval was inversely associated with being overweight in comparison with only-child in both boys (odds ratio (OR): 0.83, 95% CI, 0.72-0.96) and girls (OR: 0.75, 95% CI, 0.63-0.88). Long birth interval also showed inverse association in boys (OR: 0.78, 95% CI, 0.62-0.97), and marginal inverse association in girls (OR: 0.80, 95% CI, 0.62-1.04).
First-born children who experienced short birth intervals did not show a different overweight risk from only-child. First-born children who experienced 1.5-8 years of the birth interval had a lower risk of childhood overweight compared with only-child.
先前的研究表明，独生子女比有兄弟姐妹的同龄人更易超重，无论其是家中最大、中间还是最小的孩子。本研究的目的是明确在同胞出生前经历过幼儿期独生子女阶段的头胎子女中，独生子女阶段的时长与超重风险之间是否存在关联。
从日本一项全国性纵向调查中选取了7576名头胎男孩和7229名头胎女孩进行研究。独生子女阶段的时长由“出生间隔”确定，即头胎子女与第二个孩子出生之间的间隔。分为短（<1.5年）、中等（1.5至4年）、长（4至8年）和独生子女（第二个孩子8年未出生）。超重定义为8岁时体重指数（BMI）z评分高于1个标准差。采用逻辑回归分析独生子女阶段时长与儿童超重之间的关联，并对协变量进行校正。
与独生子女相比，中等出生间隔与男孩（优势比（OR）：0.83，95%置信区间（CI），0.72 - 0.96）和女孩（OR：0.75，95% CI，0.63 - 0.88）超重呈负相关。长出生间隔在男孩中也呈负相关（OR：0.78，95% CI，0.62 - 0.97），在女孩中呈边缘负相关（OR：0.80，95% CI，0.62 - 1.04）。
出生间隔短的头胎子女超重风险与独生子女无差异。出生间隔为1.5至8年的头胎子女儿童期超重风险低于独生子女。
