Blood pressure in children in relation to relative body fat composition and cardio-respiratory fitness

Abstract

To examine whether higher physical fitness is associated with lower levels of blood pressure independent of adiposity in an established cohort of children. We explored how the method used to adjust fitness for body size would influence the findings. Blood pressure, adiposity (DXA scan) and fitness (predicted work capacity at a heart rate of 170 bpm [PWC170]) were assessed in children aged 9 years (n = 3594). Separate regression analyses for boys and girls yielded strong linear relationships between blood pressure (dependent variable) and ratio of fat to lean + bone (independent variable; all P < 0.001). An independent effect of fitness was assessed by adding PWC170 to the above models. Blood pressure was strongly inversely related to PWC170 when the latter was first adjusted for size in the conventional way (division by weight; all P < 0.001), probably because of mathematical ?coupling? (via weight). PWC170 expressed as a residual from our own regression of PWC170 on weight showed no association with systolic blood pressure and a small negative association with diastolic blood pressure (girls P = 0.042; boys P < 0.001). Across the observed ranges of fitness, mean blood pressure differed by 1 [95% CI 0?3] mm Hg for boys and 3 [95% CI 2?4] mm Hg for girls. Fitness is not associated with systolic blood pressure independent of levels of adiposity but there is a small but independent association with diastolic blood pressure.