Age at first birth and fathers' subsequent health: evidence from sibling and twin models.

Using a sample of 540 siblings and twins from the National Survey of Midlife Development in the United States, this study examines the relationship between the age at which men become biological fathers and their subsequent health. The analysis includes both between-family models that treat brothers as independent observations and within-family models that account for unobserved genetic and early-life environmental endowments shared by brothers within families. Findings indicate that age at first birth has a positive, linear effect on men's health, and this relationship is not explained by the confounding influences of unobserved early-life characteristics. However, the effect of age at first birth on fathers' health is explained by men's socioeconomic and family statuses. Whereas most research linking birth timing to specific diseases focuses narrowly on biological mechanisms among mothers, this study demonstrates the importance of reproductive decisions for men's health and well-being.