BACKGROUND: Earlier studies on seasonality in growth reported the largest height gains during spring and largest body weight gains during autumn. We examined seasonality in height, body weight, BMI, fat mass index (FMI) and fat-free mass index (FFMI) among contemporary Danish 8-11-year-olds.

METHODS: 760 children from the OPUS School Meal Study provided >2200 measurements on height, body weight and composition between September-June. Average velocities were calculated using change-score analyses based on three-month intervals. As a complementary analysis, point velocities derived from estimated growth curves were fitted using semi-parametric regression that included covariate adjustment and allowed flexible modelling of the time trend.

RESULTS: Average velocities showed the following trends: Height was higher than the average (6.10 cm/year) in January-April. Body weight was below the average (4.02 kg/year) August-January and above January-May; BMI (average: 0.49 kg/ m(2)/year) and FFMI (average: 0.17 kg/m(2)/year) showed similar trends. In contrast, FMI was above the average (0.38 kg/m(2)/year) November-March. Similar trends were seen for point velocities.

CONCLUSIONS: Our findings suggest seasonality in growth and body composition of Danish children. We recovered the well-known height velocity peak during spring time, but unlike earlier studies we found coincident peaks in body weight, BMI, and FFMI velocities.Pediatric Research (2015); doi:10.1038/pr.2015.206.