Associations of heart rates and respiratory rates with lifestyle and environmental factors in toddlers: a nationwide cohort study

BACKGROUND: Heart rate (HR) and respiratory rate (RR) are key vital signs, yet few large studies have reported their normal values in toddlers. We thus assessed HR and RR in two-year-old Japanese children. Given that body size may influence vital signs, we first assessed the correlations of height and weight with HR and RR. We also examined associations of HR and RR with physical activity levels and residential region, as these factors have been linked to vital signs in adults. METHODS: This prospective cohort study included children from the Japan Environment and Children's Study. We measured their HR, RR, height, and weight at two years of age, and assessed their outdoor playtime from one to two years of age using a questionnaire. Participants without HR or RR data were excluded from the analysis. Descriptive statistics for HR and RR at two years of age were summarized. In addition, the correlation coefficient between the participants' height or weight and HR or RR were calculated. We investigated the association between the region or outdoor playtime and HR or RR using a one-way analysis of variance and multiple regression analyses. The covariates included medical history, mother's gestational hypertension, parents' height and weight, parents' smoking status, and parents' educational background. RESULTS: A total of 4,805 participants were included in the HR analysis, and 4,806 in the RR analysis. The mean HR and RR of were 109.2 ± 14.7 beats/min and 29.9 ± 6.1 breaths/min (mean ± standard deviation), respectively. No correlation was found between height or weight and HR or RR. The mean HR of participants who almost never spent time playing outdoors was 111.7 beats/min, whereas that of participants who spent ≥ 3 h/d playing outdoors was 108.2 beats/min (p = 0.038). The mean HR in Eastern Japan was 106.8 /min, whereas that in Western Japan was 112.7 beats/min (p < 0.001). CONCLUSION: We assessed the normal HR and RR in Japanese children aged two years, and these normal ranges did not correlate with height and weight. A longer duration of outdoor playtime was associated with a lower HR.