Lower birth weight is associated with higher resting heart rate during boyhood

There is substantial evidence that low birth weight is associated with the development of cardiovascular disease in adult life. Moreover, resting heart rate is a prognostic factor of cardiovascular morbidity and mortality. However, there are scarce data regarding the association between birth weight and resting heart rate in later life. Therefore, we investigated the association of anthropometric data at birth and hemodynamic indices including resting heart rate in Japanese boys. The data of 1,107 male students of a junior high school in Tokyo, Japan, who underwent a medical check-up in the year of admission to the school (12 or 13 years old) were used. Information on anthropometric data at birth based on "The Maternal and Child Health Handbook" was obtained from 573 students. From a standard 12-channel resting electrocardiogram, 8 cardiac cycles were used to estimate heart rate. Resting heart rate correlated positively with body mass index at the same age (r=0.100, p=0.017) and correlated negatively with birth weight (r=-0.102, p=0.015), height at birth (r=-0.125, p=0.003), and head circumference at birth (r=-0.095, p=0.025). The negative correlation of anthropometric data at birth with heart rate at the age of 12 or 13 was independent of body mass index at the same age. The mean value of resting heart rate at the age of 12 or 13 adjusted for body mass index at the same age was significantly higher in the lower tertile of birth weight than in the higher tertile of birth weight (81.7 vs. 78.5 beats/min, p=0.028). In conclusion, lower birth weight is associated with higher resting heart rate during boyhood, suggesting that elevated heart rate may be one mechanism linking small size at birth with the development of cardiovascular disease in future life.