Bullying during childhood and development of adult obesity: a co-twin control study

Background: The aetiology of adult obesity is still poorly understood. It has been shown that overweight children suffer from adverse psychological events, but less is known about the potential effects of adverse psychological factors among normal weight children for later development of obesity. The objective of this study was to examine if bullying during childhood was related to the development of obesity as adult. Methods: Adult twin pairs aged 20-50 years, who were discordant for BMI were identified from the Danish Twin Registry. Criteria for being discordant were that one twin was normal weight (BMI 30 kg/m²). A total of 146 complete twin pairs fulfilled the criteria for election and were invited to an interview and a physical examination in 2006. The bullying questionnaire developed by Olweus was used. Data was analyzed by means of a growth-curve model and an intra-pair comparison. Results: In total 236 twin individuals participated (81.7 . Discordance for obesity was related to childhood bullying such that the more bullied twin developed more obesity as adult, eg. “How often were you bullied in school” (p=0.02), “I was made a fool of” (p=0.03) and “Schoolmates spread lies about me” (p=0.002). Conclusion: This study demonstrates that being bullied in childhood is an independent risk factor for developing obesity in adulthood.