Birth order and number of siblings and their association with overweight and obesity: A systematic review and meta-analysis

Fernanda Oliveira Meller, Christian Loret de Mola, Maria Cecília Formoso Assunção, Antônio Augusto Schäfer, Darren Lawrence Dahly, Fernando Celso Barros

Research output: Contribution to journalArticlepeer-review

31 Scopus citations


Context: The effect of both birth order and number of siblings on overweight and/or obesity has not been determined. Birth order and sibsize have been mathematically coupled to overweight and/or obesity, but thus far their respective effects have been estimated separately. Objective: The aim of this systematic review was to evaluate the effects of both birth order and number of siblings on the risk of overweight/obesity. Data Sources: The electronic databases MEDLINE, Social Science, SocINDEX, PsycINFO, CINAHL Plus, and Academic Search Complete were searched systematically. Study Selection: Titles and abstracts of 1698 records were examined. After 1504 records were excluded, 2 authors independently assessed the full text of all remaining papers (n=194); disagreements were resolved by discussion. Data Extraction: A standardized form for assessment of study quality and evidence synthesis was used to extract data from the included studies. Results: Twenty studies were included in the systematic review, 14 of which were included in the meta-analysis. Meta-analyses showed that lower (vs higher) birth order and smaller (vs greater) number of siblings were associated with overweight and/or obesity, with ORs of 1.47 (95%CI, 1.12-1.93) and 1.46 (95%CI, 1.17-1.84), respectively. However, among the 9 studies that attempted to separate the effects of birth order and number of siblings in the same analysis, a higher risk of overweight/obesity was consistently found among individuals without siblings than among those with 1 or more siblings, rather than among firstborns more generally. Conclusion: The results show that both lower birth order and lower number of siblings are associated with risk of overweight/obesity, which suggests that only children are at a slightly increased risk of overweight/obesity. Systematic Review Registration: PROSPERO registration number CRD42014015135.

Original languageEnglish
Pages (from-to)117-124
Number of pages8
JournalNutrition Reviews
Issue number2
StatePublished - 1 Feb 2018
Externally publishedYes


  • Birth order
  • Meta-analysis
  • Number of siblings
  • Obesity
  • Overweight


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