Birth order and health disparities throughout the life course.

BACKGROUND

Research has shown ample evidence of how birth order affects health; however, these studies focus on specific health outcomes and ages.

OBJECTIVE

We provide a comprehensive picture of the effects of birth order on health disparities over the life course.

METHOD: We study the effects of birth order from birth to age 70 on hospitalizations, visits to open care facilities and mortality using Swedish register data from 1987 to 2016. We identify the effects by comparing siblings within the same family.

RESULTS

We find that firstborns have worse health at birth. In adolescence, the birth-order effects switch direction, and younger siblings are more likely to be hospitalized and visit open care facilities. From early age younger siblings receive more care for injuries, in adolescence for drug and alcohol abuse, and from middle age for diseases of the circulatory system compared to older siblings. Younger siblings also stay longer in hospital. Age 0-2, younger siblings are more likely to be hospitalized for infections, diseases of the respiratory system, eyes and ears, whereas the pattern is the opposite for children age 3-6. Firstborns are more likely to receive care for depression and ADHD in childhood and endocrine diseases after age 50.

INTERPRETATION: Birth order affects health over the life-cycle and this is likely due to biological factors as well as parental behavior and the family environment. Firstborns have worse health at birth, but in adolescence the effects switch direction due to health issues related to younger siblings engaging in more risky behavior. For small children, having siblings at home increases the risk of being hospitalized for infections, diseases of the respiratory system, eyes and ears. The adverse conditions in utero for firstborns may be the cause of increased risk of metabolic syndromes such as obesity and diabetes later in life.