Seasonal variability of cardiovascular parameters in elementary schoolchildren with various body mass indexes

Abstract

Children are known to have significant seasonal variability in both body mass index (BMI) and some parameters of the cardiovascular system. The aim of this study was to analyze possible differences in the seasonal variability of cardiovascular indexes in children aged 7-11 years with various BMI values.
Methods. The study included results of a 4-year dynamic monitoring of functional parameters in elementary schoolchildren (4 parallel classes) from the 1st to the 4th grade (a total of 153 students, including 82 girls and 71 boys). Measurements were performed twice a year, in early April (end of the school year) and in early October (beginning of the school year). Each examination included evaluation of anthropometry and cardiovascular indexes (2-min recording on a spiroarteriocardiorhythmograph in a sitting position). The anthropometric data were assessed with Z-scores and the BMI value percentile. The studied cardiovascular indexes included systolic blood pressure (BP), total power (TP), and the LF/HF ratio in the spectrum of heart rate variability. The seasonal variability was analyzed by changes (delta) in indexes between measurements. Children were divided into groups based on BMI values obtained in testing at the end of the 4th grade as follows: below the 15th percentile (underweight); from the 15th to 84th percentile (normal); from the 85th to 95th percentile (overweight); and above the 95th percentile (obesity).

Results. The proportion of overweight and obese children was maximal at the end of the 1st grade (28-34%) and decreased by the 4th grade to 11-15%. In contrast, by this age, the proportion of underweight children reached 44.6% for girls and 35.7% for boys. The seasonal variability of BMI was characterized by an increase in Z-scores over the school year and a decrease in Z-scores over the summer period. This was most pronounced in underweight children. The seasonal variability of cardiovascular parameters was evident as increases in BP and TP and a decrease in LF/HF over the academic year and was most pronounced in the normal group. However, no significant differences in the seasonal variability of cardiovascular indexes were observed in children from different BMI groups.
Conclusion. Seasonal variability of cardiovascular parameters in 7–11-year-old children does not depend on the BMI value.