Department of Pediatrics, Okayama University Hospital, Okayama, Japan.
Department of Pediatrics, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama, Japan.
Clin Exp Allergy. 2018 May;48(5):577-585. doi: 10.1111/cea.13100. Epub 2018 Feb 27.
Environmental factors seem to be related to the incidence of allergic disease. Children with a later birth order are often exposed to environments, where pathogens and endotoxins can be found, and thus have a higher risk of developing infectious diseases. Therefore, birth order is regarded as an indicator that reflects post-natal environment. However, longitudinal studies are limited on this subject. This study sought to elucidate the relationships between birth order and allergic disease.
From a nationwide longitudinal study that followed children born in 2001 (n = 47 015), we selected doctors' visits for 3 types of allergic disease-bronchial asthma, food allergy and atopic dermatitis-from infancy to 12 years of age and conducted binomial log-linear regression analysis to evaluate the associations between birth order and these diseases. We adjusted for the child and parental factors and estimated risk ratio (RR) and 95% confidence interval (CI) for each outcome.
The associations between birth order and bronchial asthma were diverse; later birth order increased the risk in early childhood, but decreased the risks during school age. For example, the adjusted RR comparing third-born or higher and first-born children was 1.19 (95% CI, 1.05-1.35) between 30 and 42 months of age, but was 0.76 (95% CI, 0.65-0.89) between 10 and 11 years. Later birth order was generally protective for food allergy but increased the risk of atopic dermatitis.
The influence of birth order depended on the type of allergic disease and the childhood period. Childhood is unique in terms of physical and immunological development, and the immune response to the post-natal environment in childhood appears to be heterogeneous.
环境因素似乎与过敏疾病的发生有关。晚出生的孩子通常会接触到病原体和内毒素等环境，因此患传染病的风险更高。因此，出生顺序被认为是反映产后环境的一个指标。然而，关于这个问题的纵向研究有限。本研究旨在阐明出生顺序与过敏疾病之间的关系。
我们从一项针对 2001 年出生的儿童（n=47015）的全国性纵向研究中，选择了从婴儿期到 12 岁的 3 种过敏性疾病（支气管哮喘、食物过敏和特应性皮炎）的就诊记录，并进行二项逻辑线性回归分析，以评估出生顺序与这些疾病之间的关系。我们调整了儿童和父母的因素，并估计了每个结果的风险比（RR）和 95%置信区间（CI）。
出生顺序与支气管哮喘的关系是多样化的；晚出生顺序会增加幼儿期的风险，但会降低学龄期的风险。例如，在 30 至 42 个月时，与第一胎相比，第三胎或更高胎次的儿童患支气管哮喘的调整 RR 为 1.19（95%CI，1.05-1.35），而在 10 至 11 岁时，调整 RR 为 0.76（95%CI，0.65-0.89）。晚出生顺序通常对食物过敏有保护作用，但会增加特应性皮炎的风险。
出生顺序的影响取决于过敏疾病的类型和儿童期。儿童期在身体和免疫发育方面具有独特性，儿童期对产后环境的免疫反应似乎是异质的。
