Association among number, order and type of siblings and adolescent mental health at age 12

Background Although the sibling relationship is a unique one, the effects of the number and type of siblings on mental health among adolescents have not been reported. Methods Japanese children (total, 9276; boys, 4654; girls, 4622), all 12 years old, and from the Japanese Toyama Birth Cohort Study, were followed up until 2002. Subject self-reported mental health was obtained from the Japanese version of the Dartmouth Primary Care Co-operative Project (COOP) charts. The associations between number and type of siblings and self-reported mental health were examined. Results There was a significant difference in mental health between different sibling pairs, with brother pairs and brother/sister pairs having a positive effect on adolescent mental health, compared with those in sister pairs. Girls with brothers had better self-reported mental health than those without. The adjusted OR of good mental health was 1.44 (95%CI:1.00-2.08) for those with an older brother and 1.67 (95%CI: 1.17-2.38) for those with a younger brother compared with those without. Boys with a younger sister had a higher OR of good self-reported health than those without (OR, 1.62; 95%CI: 1.08-2.43). Conclusions Children with siblings had better mental health status than those without, which has practical implications for Asian countries and worldwide considering the declining fertility.