Secular trends in physical growth indicators in infants and young children

Abstract

There have been no analyses in Japan that have used mathematical functions to investigate changes over time in physical growth records of infants and young children. In this study, we investigated secular changes in physical growth velocity of infants and young children using the wavelet interpolation method, and examined secular changes in physical growth indicators. The subject data were physical growth survey records for young boys and girls published by the Ministry of Health, Labor and Welfare in 1960 and 2000. The physical growth indicators used in the study were height, weight, chest circumference and head circumference. The wavelet interpolation method was applied to these indicators for the period from age 0 to 6 years, and the derived growth distance curves and growth velocity curves were analyzed. The values at birth were higher in 1960 than in 2000 for both boys and girls, but after 6 months of age the values for 2000 exceeded those for 1960. The largest peak velocity soon after birth, obtained from the analysis of the growth velocity curve, did not show clear secular changes in either boys or girls. However, a clear increasing trend was seen in the largest peak velocity for all indicators in both boys and girls in 2000, compared with 1960. The age at first local peak velocity remained unchanged in boys in 2000 compared with 1960, but in girls slightly earlier trends were seen in all indicators in 2000. Thus, this investigation of the secular changes in physical growth indicators in infants and young children indicated that in 2000 children were slightly smaller at birth, but then matured more quickly, and grew larger than children in 1960.