To Örebro University

The aim was to investigate whether older siblings are associated with development of stress resilience in adolescence and if there are differences by sex of siblings. The study used a Swedish register-based cohort of men (n=664 603) born between 1970 and 1992 who undertook military conscription assessments in adolescence that included a measure of stress resilience: associations were assessed using multinomial logistic regression. Adjusted relative risk ratios (95% confidence intervals) for low stress resilience (n=136 746) compared with high (n=142 581) are 1.33 (1.30, 1.35), 1.65 (1.59, 1.71) and 2.36 (2.18, 2.54) for one, two and three or more male older siblings, compared with none. Equivalent values for female older siblings do not have overlapping confidence intervals with males and are 1.19 (1.17, 1.21), 1.46 (1.40, 1.51) and 1.87 (1.73, 2.03). When the individual male and female siblings are compared directly (one male sibling compared with one female sibling, etc.) and after adjustment, including for cognitive function, there is a statistically significant (p<0.005) greater risk for low stress resilience associated with male siblings. Older male siblings may have greater adverse implications for psychological development, perhaps due to greater demands on familial resources or inter-sibling interactions.