Abstract
Objective. 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. Methods and Results. 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. Conclusions. 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.
Acknowledgements
We are extremely grateful to all the families who took part in this study, the midwives for their help in recruiting them, Kate Northstone (our ‘Data Buddy’) and the whole ALSPAC team, which includes interviewers, computer and laboratory technicians, clerical workers, research scientists, volunteers, managers, receptionists and nurses. The UK Medical Research Council, the Wellcome Trust and the University of Bristol provide core support for ALSPAC.
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.