The effect of increased dairy consumption during one week of intense training on serum bone markers of adolescent female athletes

Abstract

While high-impact exercise training typically has a positive effect on bone, intensified training during adolescence, the period of rapid growth and peak bone acquisition, could potentially have an opposite effect. Dairy foods contain bone-supporting nutrients (i.e., calcium) that are crucial to the structural integrity and strength of bone. In this study, 13 female adolescent soccer players (14.3 ± 1.3y) participated in a cross-over, randomized, double-blind trial examining the effects of Greek yogurt (GY) consumption on bone biomarkers during a one-week period of intensified training. The study took place over two intervention weeks, which consisted of a pre-training assessment day, 5-days of consecutive, intense soccer training and a post-training assessment day. Participants completed both the GY condition, and a carbohydrate isocaloric placebo control pudding condition (CHO) condition in random order, 4 weeks apart. Fasted, resting blood samples were collected in the morning at pre- and post-training sessions during each intervention condition. Total osteocalcin (tOC), undercarboxylated osteocalcin (unOC), carboxyl-terminal telopeptide of type 1 collagen (CTX), osteoprotegerin (OPG), and receptor activator nuclear factor kappa-β ligand (RANKL) were measured in serum. Results showed no significant effects for time (from pre- to post-training) and condition, and no interaction in tOC, CTX, OPG, RANKL and OPG/RANKL ratio. There was an interaction (p=0.011) for unOC, which decreased significantly at the end of the intense training period in the GY condition, but not in the CHO condition (-26% vs -3%, respectively). Relative unOC, expressed as a percentage of tOC, also reduced post-training (-16%), but with no differences between intervention conditions. These findings suggest that high-impact intense training had no direct catabolic impact on bone metabolism, at least in the short-term, and thus, GY added no benefit beyond that of the isocaloric CHO control pudding.