Overvekt og fedme blant barn i Gjerdrum kommune-en retrospektiv kohortstudie av helsestasjonsdata for årskullene 1996-2005

Background: Overweight and obesity are major health concerns as the conditions increase the risk for sickness and early death, and may start early in life. To organize targeted health services there is a need for more knowledge about the development of childhood obesity, in particular about vulnerable periods for increases in prevalence and also about the degree of persistency when overweight or obesity is present during childhood. Purpose: This study aimed to get valid knowledge about the prevalence and development of overweight and obesity among children on the basis of longitudinal data (repeated measurements) from the primary health care center in Gjerdrum municipality, Norway. Material and methods: A retrospective cohort study of 893 children born in 1996 – 2005 was conducted. Data on weight and height from the primary health care center were collected and body mass index was calculated. Children (≥ two years) were categorized as having normal weight, overweight, being obese or severe obese according Coles Index. Results: The prevalence of overweight and obesity increased from 13 percent at school start to 20 percent at the end of primary school. Children who were overweight or obese at school start had a substantially increased risk of being overweight or obese in the seventh or eighth grade, compared with those who were normal weighted at school start (Relative Risk 4,6 (2,12 – 10,09)). Equivalent risk for overweight and obesity at four years was 4,0 (1,58 – 10,14). There was no clear time trend in mean BMI and prevalence of overweight and obesity, but severe obesity was observed at school start among those born in 2001. Finally, there was a trend towards girls being more overweight or obese than boys (apart from two years of age). Conclusions: This study showed that the prevalence of overweight and obesity increased during childhood and thus there is a need for obesity prevention in primary school. Those who were overweight or obese from the age of four had a much larger risk for persisting overweight and obesity and these children need appropriate treatment. This study could not say whether or not the obesity prevalence had increased during the observation period of ten years because the prevalence varied a great deal between the cohorts.