Analysis of factors that influence body mass index from ages 3 to 6 years: A study based on the Toyama cohort study

Background: The aim of the present study was to elucidate both environmental and behavioral factors that influence body mass index (BMI, kg/m(2)) among Japanese children from ages 3-6. Methods: In 1992 (at age 3) and 1995 (at age 6), 8170 6-year-old children (4176 boys and 3994 girls) were surveyed using a questionnaire on both body build (height and weight) and lifestyle. The correlation between BMI for 3-year-olds and for 6-year-olds were analyzed. From the temporal changes of body build between age 3 and 6 years, we categorized children into four groups: group 1, normal at both age 3 years and 6 years (normal/normal); group 2, overweight at age 3 years and normal at age 6 years (overweight/normal); group 3, normal at age 3 years and overweight at age 6 years (normal/overweight); and group 4, overweight at both age 3 years and 6 years (overweight/overweight). The authors compared the four groups with each other according to sex, concerning frequencies of children who matched the categories of environmental and behavioral factors. Each factor was tested using the chi(2) test. Overweight children were defined as those whose BMI value was age-sex specific in the 90th percentile or more. Results: A significant correlation was found between body builds for children aged 3 and 6 years in both genders (boys, r = 0.559, P < 0.01; girls, r = 0.584, P < 0.01). Significant factors associated with overweight children were diet (eating rice, green tea, eggs, meat, but less breads and juice), rapid eating, short sleep duration, early bedtime, long periods of television viewing, avoidance of physical activity, and frequent bowel movement. Discussion: Temporal changes in BMI from age 3 years to 6 years are significantly associated with both environmental and behavioral factors at age 6 years. The results of this study may be useful for health promotion programs designed to prevent obesity during the early stages of childhood.