Background: Children's lifestyles have changed recently in Japan. These changes are thought to be associated with their physical growth. The aim of the present paper was to describe and interpret the growth seasonality of children attending day-nurseries in Osaka Prefecture, Japan.
Methods: Results were based on a 6 year follow-up study of preschool children aged 0 at baseline to 6 years old at the end of the follow up. Longitudinal growth data for 148 boys and 113 girls, born between April 1990 and March 1991, attending day-nursery were obtained monthly from April 1990 through to March 1996. Children were divided into two groups: those with a normal (<17) or high (≥17) body mass index (BMI) at 5 years of age. Weight and height seasonal gains were estimated for each group.
Results: Weight gain was higher during autumn among the group with a normal BMI at 5 years of age. Among high BMI group, weight gain was higher during autumn when they were 0 to 4 years of age, while it was higher during summer when they were 5 years of age. Height gain was higher in spring and summer in both BMI groups. Results were similar in boys and girls.
Conclusion: Although the findings are consistent with previous studies for normal BMI children, the present study reports new findings for children with a high BMI at 5 years of age, for whom a large weight gain occurred during summer.