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

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。基本原理虽然运动有益于骨骼健康是普遍事实，但在某些情况下，运动可能与骨矿物质密度(BMD)的丧失有关。在这项初步研究中，我们将评估出汗导致的钙流失对骨密度的影响。一项关于运动员钙流失和骨密度的研究发现，在一个赛季中，男大学生篮球运动员的总骨密度显著下降。当同样的运动员在接下来的比赛季节以补钙运动饮料的形式补充钙时，骨密度增加了，而不是减少了。为了进一步探索汗水中钙流失的潜在作用，我们选择了在竞技公路自行车手中进行这项研究。他们的高训练量(10-15小时/周或更多)预计会产生大量的汗水钙损失。此外，公路自行车的训练/比赛季节相对较长(1月至9月)，适合确定对骨代谢的影响。我们选择研究公路自行车者的另一个原因是，他们似乎面临更高的低骨密度风险。6-12在这项初步研究中，我们将研究通过汗水丢失钙作为骨密度丢失的一个潜在机制。然而，剧烈运动也被发现扰乱了人类的性激素和压力荷尔蒙水平。13-16剧烈运动也可能导致全身炎症。17-19这些变化也可能影响骨骼代谢。目的和假设：这项初步研究的主要目标是以前瞻性的、受控的方式评估一种潜在的机制，通过这种机制，剧烈的、长期的运动(包括锻炼回合的长度和训练/竞技赛季的持续时间)可能会促进骨丢失。我们的假设如下：H1：在一个赛季的训练和比赛中，长时间的高强度运动训练导致的皮肤钙丢失是竞技公路自行车手骨丢失的一个重要决定因素。将钙的摄入量增加到高于目前推荐的水平(2000毫克/天)，将在一个赛季的训练和比赛中减轻竞技公路自行车手的骨质流失。方法：为了解决这些假设，我们将研究20名经过一个赛季的训练和比赛的竞技自行车运动员。参赛者将是18-35岁的男性，他们已经参加了两个赛季或更多的比赛，每周训练10个小时或更多。他们的基础钙摄入量将达到或低于推荐的每天1000毫克的摄入量。他们将随机服用安慰剂或补钙剂1800-2000毫克/天，或维持通常的1000-1200毫克/天的摄入量。参赛者将在基线、赛季中期和赛季结束后在固定训练器上进行2小时的模拟训练。在这些访问中将测量BMD，并通过测量汗液钙浓度和确定汗液损失(根据经水分消耗和尿液产生校正的体重变化估计)来确定他们汗液钙损失的估计。分析：我们的主要结果衡量指标是安慰剂未补充组与补钙组的骨密度。我们将尝试控制混杂因素，如性激素和应激激素的变化，炎症因子，以及整个季节体重的变化。

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.