Midway evaluation - Bente Brannsether-Ellingsen
Overweight and obesity in the growing child
Background: There has been an alarming increase in childhood overweight and obesity all over the world. Data from the Bergen Growth Study (BGS) have shown an increase in weight for height when compared with data from the 1970s, particularly among 7-11 year old children, with about every fifth child being overweight or obese. Obesity tracking throughout childhood represents a consistent predictor of adult metabolic risk.
There is international consensus to use body mass index (BMI; kg/m²) in defining overweight and obesity. According to the International Obesity Task Force (IOTF) overweight is defined in adults as an equivalent of BMI ≥ 25 kg/m², and similar for obesity a BMI ≥ 30 kg/m². Sex and age adjusted cut-offs are used for children.
BMI can be biased by height and muscle mass and does not give information about body fat distribution. It has long been recognized that the distribution of body fat influences disease risk. Large waist circumferences in adulthood are linked with early death regardless of BMI. Waist circumference and waist-to-height ratio have been shown to correlate with amount of abdominal fat, as well as cardio metabolic risk factors also in children. Data from other countries have shown a more rapid increase in waist circumference in children than BMI. Skinfold thickness measures subcutaneous fat and have proven to correlate with adverse health risk, as well as being able to predict % body fat better than BMI.
The existing skinfold references of Norwegian children date back to the 1970`s. We have no information on central fat distribution in the normal Norwegian child population, and there is little information on timing of weight gain and critical ages for the development of overweight and obesity.
Aims: The current study has two focus areas; A) BMI versus other weight related anthropometric traits and B) Timing of weight gain and critical ages for the development of overweight.
Methods: The study is a part of The Bergen Growth Study (www.vekststudien.no), a cross-sectional study that was conducted from 2003 to 2007. Children 0-19 years of age (8299 participants), from the city of Bergen were recruited in a stratified random selection of well-baby centers, kindergartens, primary and secondary schools. The children were measured on ten different anthropometric variables. About 50% of all the school-children recruited to the BGS were measured again one year later with measurement of height and weight. Data on factors that could affect growth and weight development was collected through parental questionnaire. For this study we use different cohorts of children from the BGS. Various statistical techniques are used to construct percentiles, suggest cut-offs and describe the data and associations.
Results: In our first two papers we presented current distribution with percentiles, for waist circumference and waist-to-height ratio in 4-18 year old children, and subscapular and triceps skinfold in 4-16 year old children. We were able to suggest single cut-offs that could be used through all ages in relation to IOTF based overweight and obesity for waist circumference, subscapular and triceps skinfold. It was not possible to define a single cut-off for waist-to-height ratio. In our third paper we studied associations between different anthropometric variables and overweight during childhood. Waist circumference SDS and waist to height ratio SDS were strongest correlated to BMI SDS through all ages and in both sexes. When adjusted for all other variables, waist circumference SDS contributed most to the variation in BMI SDS. Age group, but not sex, contributed significantly to variation in BMI SDS. For all variables the correlations were weakest in the youngest age group and highest between 7-12 years.
We are currently working on a forth paper investigating on one year increments of height, weight and BMI with focus on timing of weight gain and critical ages for the development of overweight and obesity.
- Brannsether B, Roelants M, Bjerknes R,Júlíusson P. Waist circumference and waist to height ratio in Norwegian children 4-18 years of age; reference values and cut-off levels. Acta Paediatr 2011, 100: 1576-82
- Brannsether B, Roelants M, Bjerknes R, Júlíusson P. References and cut-offs for triceps and subscapular skinfolds in Norwegian children 4-16 years of age. Eur J Clin Nutr, 2013, 928-33.
- Brannsether B, Eide GE, Roelants M, Bjerknes R, Jùlìusson P. Interrelationships Between Anthropometric variables and Overweight in Childhood and Adolescence. Amer J Hum Biology. Online April 2014.