Association Among Cardiorespiratory Fitness, Body Fat, and Bone Marker Measurements in Healthy Young Females

Context: Serum vitamin D (25-hydroxyvitamin D [25(OH)D]) is important for maintaining bone health, as well as for influencing a multitude of nonosseous effects. Associations between 25(OH)D and other bone marker measurements have not been well studied in relation to obesity and cardiorespiratory fitness in healthy young females. Objective: To determine if there is an association of cardiorespiratory fitness and body fat with bone marker measurements (ie, 25[OH]D and calcium) in healthy young females at peak bone mass. Methods: Females younger than 25 years were recruited as volunteer participants. From July 2007 to October 2007, participants were assessed for cardiorespiratory fitness by measuring maximal oxygen consumption (VO₂ max). In addition, their levels of serum 25(OH)D and serum total calcium were analyzed. Finally, percent body fat was measured using dual-energy x-ray absorptiometry of the whole body. Pearson correlation coefficients were used to evaluate the association of fitness and body fat with bone marker measurements. Results: A total of 59 adolescent girls and young womenwere recruited. A statistically significant, positive association was found between VO₂ max and serum 25(OH)D levels (Pearson r=0.36; P<.05), but not between VO₂ max and serum total calcium levels (Pearson r= -0.10, P<.05). Percent body fat was inversely associated with both VO₂ max (Pearson r= -0.70, P<.05) and 25(OH)D levels (Pearson r= -0.44, P<.05). Conclusion: In healthy young females, better cardiorespiratory fitness, as measured by VO₂ max level, and lower percent body fat are associated with higher serum 25(OH)D level. This response is independent of serum total calcium level.