Max Planck Research Group Lifecourse Dynamics and Demographic Change, Max Planck Institute for Demographic Research, Rostock, Germany.
J Epidemiol Community Health. 2013 Jul;67(7):571-7. doi: 10.1136/jech-2012-202296. Epub 2013 May 3.
Birth order is associated with outcomes such as birth weight and adult socioeconomic position (SEP), but little is known about the association with adult height. This potential birth order-height association is important because height predicts health, and because the association may help explain population-level height trends. We studied the birth order-height association and whether it varies by family characteristics or birth cohort.
We used the Swedish Military Conscription Register to analyse adult height among 652,518 men born in 1951-1983 using fixed effects regression models that compare brothers and account for genetic and social factors shared by brothers. We stratified the analysis by family size, parental SEP and birth cohort. We compared models with and without birth weight and birth length controls.
Unadjusted analyses showed no differences between the first two birth orders but in the fixed effects regression, birth orders 2, 3 and 4 were associated with 0.4, 0.7 and 0.8 cm (p<0.001 for each) shorter height than birth order 1, respectively. The associations were similar in large and small and high-SEP and low-SEP families, but were attenuated in recent cohorts. Birth characteristics did not explain these associations.
Birth order is an important determinant of height. The height difference between birth orders 3 and 1 is larger than the population-level height increase achieved over 10 years. The attenuation of the effect over cohorts may reflect improvements in living standards. Decreases in family size may explain some of the secular-height increases in countries with decreasing fertility.
出生顺序与出生体重和成人社会经济地位（SEP）等结果有关，但人们对其与成人身高的关系知之甚少。这种潜在的出生顺序-身高关联很重要，因为身高可以预测健康，而且这种关联可能有助于解释人群身高趋势。我们研究了出生顺序与身高的关系，以及这种关系是否因家庭特征或出生队列而异。
我们使用瑞典兵役登记处的数据，分析了 1951 年至 1983 年出生的 652518 名男性的成人身高，使用固定效应回归模型，该模型比较了兄弟之间的身高，并考虑了兄弟之间共享的遗传和社会因素。我们根据家庭规模、父母 SEP 和出生队列对分析进行分层。我们比较了包含和不包含出生体重和出生长度控制的模型。
未调整的分析显示，前两个出生顺序之间没有差异，但在固定效应回归中，出生顺序 2、3 和 4 分别比出生顺序 1 矮 0.4、0.7 和 0.8 厘米（p<0.001）。这些关联在大家庭和小家庭以及高 SEP 和低 SEP 家庭中相似，但在最近的队列中有所减弱。出生特征并不能解释这些关联。
出生顺序是身高的一个重要决定因素。出生顺序 3 和 1 之间的身高差异大于 10 年内人群身高增长的幅度。随着队列的变化，这种效应的减弱可能反映了生活水平的提高。家庭规模的减少可能解释了一些生育率下降的国家中身高的长期增长。
