Determination of RDA for Vitamin D in Caucasian and African American Women

描述（由申请人提供）：骨质疏松症在美国的患病率很高，大约有1000万50岁以上的人已经患有骨质疏松症，另有3400万人有骨质疏松症的风险。卫生局局长首次发布的关于骨骼健康的报告强调了这一公共卫生问题的严重性。开发低成本和有效的策略对于预防骨质疏松症和减少骨质疏松性骨折至关重要。预防骨质疏松症的一种简单廉价的策略是摄入充足的钙和维生素D。血清25OHD现在被认为是衡量维生素D营养的客观指标。越来越多的人认识到，血清25-羟基维生素D （25OHD）浓度至少为30-32 ng/ml是最佳骨骼健康所需的，此时血清甲状旁腺激素（PTH）浓度达到最低。目前还没有系统性的前瞻性剂量反应研究，旨在确定维持人群中最佳血清25OHD水平所需的维生素D最佳摄入量，这将有助于确定维生素D的估计平均需取量（EAR）和推荐膳食需取量（RDA）。拟议的建议旨在通过关注60-85岁绝经后妇女的高风险群体来填补这一空白。我们假设，在冬季补充维生素D的97%的研究对象中，将血清25OHD增加到大于30 ng/ml或更高的水平，将降低维生素D不足（血清25OHD <20 ng/ml）的绝经后妇女在钙摄入充足的情况下的血清PTH。我们假设97%的受试者达到血清25OHD （30ng /ml）的维生素D剂量约为4400IU/天，远高于老年人维生素D的建议摄入量400- 600id。在一项为期一年的双盲、随机前瞻性临床试验中，我们将研究冬季补充不同剂量维生素D3对绝经后白种人和非裔美国人维生素D缺乏症妇女血清25OHD和PTH的剂量反应效应，这是主要的结局指标。此外，还将研究不同维生素D3补充剂量对钙吸收、1,25-二羟基维生素D水平、血清钙、骨标志物、骨矿物质密度和跌倒的影响，并将其作为我们的次要结果指标。我们希望这项建议的结果将为更容易患骨质疏松症的绝经后妇女提供维生素D的RDA的重要信息。食品和营养委员会的钙和相关营养素小组建议开展更多工作来确定维生素D的RDA。这项研究的结果也将有助于设计未来更大规模的临床试验，研究维生素D对跌倒和骨折的影响。

DESCRIPTION (provided by applicant): The prevalence of osteoporosis is high in United State with about 10 million people over the age of 50 already having the disease and another 34 million at risk for developing osteoporosis. The release of first ever Surgeon General's report on the topic of bone health emphasizes the enormity of this public health problem. Development of low-cost and effective strategies is important for prevention of osteoporosis and to reduce osteoporotic fractures. A simple inexpensive strategy to prevent osteoporosis is adequate nutrition with calcium and vitamin D. Serum 25OHD is now accepted as the objective measure of vitamin D nutrition. There is a growing understanding that serum 25-hydroxy vitamin D (25OHD) concentrations of at least 30-32 ng/ml are needed for optimal bone health at which serum parathyroid hormone (PTH) concentrations reach a minimum. There are no systematic prospective dose response studies aimed at determining the optimum amount of vitamin D intake required to maintain optimum serum 25OHD levels in the population which will help in determining the estimated average requirement (EAR) and recommended dietary requirement (RDA) for vitamin D. The proposed proposal is aimed at filling this gap by concentrating on the high risk group of postmenopausal women between age 60-85 years. We hypothesize that increasing serum 25OHD to a level greater than 30 ng/ml or more in 97% of the study subjects with vitamin D supplements in winter will reduce serum PTH in the high risk group of vitamin D insufficient (serum 25OHD <20 ng/ml) postmenopausal women in the presence of an adequate intake of calcium. We postulate that the dose of vitamin D that will achieve a serum 25OHD of > 30 ng/ml in 97% of the subjects is approximately 4400IU/day which is well above the suggested adequate intake of 400-600 ID recommended for vitamin D for the elderly. In a one year double blind, randomized prospective clinical trial, we will examine the dose response effect of supplementation with different doses of vitamin D3 in postmenopausal Caucasian and African American women with hypovitaminosis D in winter, on serum 25OHD and PTH which are the primary outcome measures. Also, the effect of various vitamin D3 supplement doses on calcium absorption, 1,25-dihydroxy vitamin D levels, serum calcium, bone markers, bone mineral density and falls will be studied and constitute our secondary outcome measures. We expect that the results from this proposal will add important information about the RDA for vitamin D for postmenopausal women who are more susceptible to osteoporosis. More work to determine the RDA for vitamin D has been recommended by the Panel on Calcium and Related Nutrients of the Food and Nutrition Board. The results from this study will also help in designing future larger clinical trials of the effect of vitamin D on falls and fractures.