BACKGROUND: Overweight and obesity in children has reached epidemic proportions in recent decades, and even the youngest age groups are affected. Excess weight during childhood often follows the child into adulthood and is associated with diseases such as cardiovascular diseases and type 2 diabetes mellitus. In addition, excess weight often leads to health problems already during childhood. Childhood obesity is therefore one of the greatest public health challenges of the 21st century.

AIM: The overall aim was to study growth patterns and early risk factors for overweight, obesity and an elevated waist-to-height ratio (WHtR) in preschool children. The specific aims were to: examine early body mass index (BMI) and WHtR growth patterns and their ability to predict overweight or obesity in children at 5 years of age (Paper I); examine if BMI and WHtR growth patterns from an early age could identify children with an elevated WHtR at 5 years of age by using standard deviation score(s) (SDS) in children classified according to WHtRSDS at 5 years of age. Another aim was to study the association between BMISDS and WHtRSDS at 5 years of age (Paper II); examine nutrition- and feeding practice-related risk factors for rapid weight gain during the first 0–6 months and the following 6–12 months (Paper III); examine the association between potential early risk factors and an elevated WHtR, defined as WHtRSDS ≥ 1 at 5 years of age, and examine whether similar associations also were found for overweight or obesity at the same age (Paper IV).

METHODS: This project was part of the population-based birth cohort study the Halland Health and Growth Study, including 2,666 children born in the county of Halland in the southwestern part of Sweden between October 2007 and December 2008. Weight, height and waist circumference were measured at nine time points starting at birth. At every measurement point the parents filled in questionnaires regarding their child’s nutrition, health and lifestyle and also background information about the family.

RESULTS: We found that children with overweight or obesity at 5 years of age could be identified already from an early age by significantly higher mean BMISDS and WHtRSDS than corresponding values in children with normal weight or underweight. BMI was sufficient for predicting overweight or obesity at 5 years of age and WHtR did not add any further information in this prediction.

Children with a WHtRSDS ≥ 1 at 5 years of age could be identified already from an early age by significantly higher mean BMISDS and WHtRSDS than corresponding values in children with a WHtRSDS < 1. When comparing WHtRSDS and BMISDS at 5 years of age, 55% of the children with an elevated WHtRSDS had normal BMISDS.

Rapid weight gain was more common during the first 6 months of the first year than during the next 6 months. Bottle-feeding and nighttime meals containing formula milk were associated with rapid weight gain between 0 and 6 months. Breastfeeding was negatively associated with rapid weight gain during the same period.

Rapid weight gain during 0–6 months and also maternal pre-pregnancy BMI and paternal BMI were associated with a WHtRSDS ≥ 1 at 5 years of age. Rapid weight gain during both 0–6 and 6–12 months and also maternal pre-pregnancy BMI, were associated with overweight or obesity at 5 years of age.

CONCLUSION: This thesis showed that BMI was sufficient for predicting overweight or obesity at 5 years of age, and WHtR did not add any further information to this prediction. For identification of children with an elevated WHtR, BMI classification missed every second child, indicating that WHtR adds value in children who may need further investigation regarding cardiometabolic risk factors. Risk factors operating before pregnancy and early in life increase the risk of early rapid weight gain, an elevated WHtR and overweight or obesity at 5 years of age and bottle feeding, nighttime meals, early rapid weight gain as well as parental overweight are potential modifiable risk factors in this development.