Birth Order and Physical Fitness in Early Adulthood: Evidence from Swedish Military Conscription Data
2014 (English)In: Social Science and Medicine, ISSN 0277-9536, E-ISSN 1873-5347, Vol. 123, 141-148 p.Article in journal (Refereed) Published
Physical fitness at young adult ages is an important determinant of physical health, cognitive ability, and mortality. However, few studies have addressed the relationship between early life conditions and physical fitness in adulthood. An important potential factor influencing physical fitness is birth order, which prior studies associate with several early- and later-life outcomes such as height and mortality. This is the first study to analyse the association between birth order and physical fitness in late adolescence. We use military conscription data on 218,873 Swedish males born between 1965 and 1977. Physical fitness is measured by a test of maximal working capacity, a measure of cardiovascular fitness closely related to V02max. We use linear regression with sibling fixed effects, meaning a within-family comparison, to eliminate the confounding influence of unobserved factors that vary between siblings. To understand the mechanism we further analyse whether the association between birth order and physical fitness varies by sibship size, parental socioeconomic status, birth cohort or length of the birth interval. We find a strong, negative and monotonic relationship between birth order and physical fitness. For example, third-born children have a maximal working capacity approximately 0.1 (p<0.000) standard deviations lower than first-born children. The association exists both in small (3 or less children) and large families (4 or more children), in high and low socioeconomic status families, and amongst cohorts born in the 1960s and the 1970s. While in the whole population the birth order effect does not depend on the length of the birth intervals, in two-child families a longer birth interval strengthens the advantage of the first-born. Our results illustrate the importance of birth order on physical fitness, and suggest that the first-born advantage already arises in late adolescence.
Place, publisher, year, edition, pages
Elsevier, 2014. Vol. 123, 141-148 p.
Birth Order, Physical Fitness, Sibling Comparison, Fixed Effects, Military Conscription Data, Sweden, Register Data
Sociology (excluding Social Work, Social Psychology and Social Anthropology)
Research subject Demography; Sociology
IdentifiersURN: urn:nbn:se:su:diva-108833DOI: 10.1016/j.socscimed.2014.11.007ISI: 000347021800017OAI: oai:DiVA.org:su-108833DiVA: diva2:760833
FunderEU, European Research Council, 2013-StG-336475