SPLMNTL CALCIUM TO OFFSET BONE MINERAL DENSITY LOSS IN COMPETITIVE MALE CYCLISTS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Rationale Although it is generally true that exercise is beneficial for bone health,1 under certain conditions exercise can be associated with loss of bone mineral density (BMD). In this pilot study, we will evaluate the impact of calcium (Ca) loss through sweating on bone density. One study of calcium loss and bone density in athletes4 found that male college basketball players had significant decreases in total BMD over the course of a season. When the same athletes were given supplemental Ca in the form of a Ca-fortified sports drink the following competitive season, there was an increase in BMD rather than a loss. To further explore the potential role of calcium loss through sweat, we have chosen to conduct the study in competitive road cyclists. Their high training volume (10-15 h/wk or more) is expected to generate a large sweat Ca loss. Also, the training/competitive season for road cycling is relatively long (Jan to Sept), which is suitable for determining the effects on bone metabolism. Another reason we chose to study road cyclists is because they appear to be at increased risk for low BMD.6-12 We will examine the loss of calcium through sweat in this pilot study as one potential mechanism of loss of BMD. However, strenuous exercise has also been found to disrupt sex and stress hormone levels in humans.13-16 Strenuous exercise may also result in systemic inflammation.17-19 These alterations may also effect bone metabolism. Aims and Hypotheses: The primary goal of this Pilot Study is to evaluate in a prospective, controlled fashion a potential mechanism by which vigorous, prolonged exercise (both in terms of length of an exercise bout and duration of the training/competitive season) may promote bone loss. Our hypotheses are as follows: H1: Dermal Ca loss as a result of prolonged, vigorous exercise training is a significant determinant of bone loss in competitive road cyclists over a season of training and competition. H2: Increasing Ca intake to higher than currently recommended levels (2000 mg/d) will attenuate the loss of bone in competitive road cyclists over a season of training and competition. Methods: To address these hypotheses, we will study 20 competitive cyclists over a season of training and competition. Participants will be men aged 18-35 yr who have been racing for 2 or more seasons and train 10 or more hours/week. They will have baseline calcium intakes at or below the recommended daily allowance of 1000mg/day. They will be randomized to take placebo or supplemental calcium to 1800-2000mg/day or maintain their usual intake of 1000-1200mg/day. Participants will perform a 2 hour simulated training ride on a stationary trainer at baseline, mid-season, and after the season ends. BMD will be measured at these visits, and estimates of their sweat calcium loss will be determined by measuring sweat calcium concentrations and determining sweat loss (estimated from change in body weight corrected for water consumption and urine production). Analysis: Our primary outcome measure is BMD in the placebo non-supplemented vs. the calcium supplemented group. We will attempt to control for confounders such as changes in sex and stress hormones, inflammatory makers, and change in body weight through the season.