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

描述（由申请人提供）：骨质疏松症的患病率在美国很高，约有1000万50岁以上的人已经患有这种疾病，另有3400万人有患骨质疏松症的风险。有史以来第一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非常重要。预防骨质疏松症的一个简单廉价的策略是钙和维生素D的充足营养。血清25 OHD现在被认为是维生素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（25 OHD）浓度至少为30-32 ng/ml是最佳骨骼健康所需的，在此浓度下，血清甲状旁腺激素（PTH）浓度达到最低值。尚无系统性前瞻性剂量反应研究旨在确定维持人群最佳血清25 OHD水平所需的最佳维生素D摄入量，这将有助于确定维生素D的估计平均需求量（OHD）和推荐膳食需求量（RDA）。拟议的提案旨在填补这一空白，重点关注60-85岁绝经后妇女的高风险群体。我们假设，在冬季补充维生素D的97%的研究对象中，血清25 OHD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25 OHD <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，在97%的受试者中达到血清25 OHD> 30 ng/ml的维生素D剂量约为4400 IU/天，这远高于老年人维生素D推荐的400-600 ID的建议摄入量。在一项为期一年的双盲、随机前瞻性临床试验中，我们将研究冬季绝经后患有维生素D缺乏症的白人和非洲裔美国妇女补充不同剂量维生素D3对血清25 OHD和PTH（主要结局指标）的剂量反应效应。此外，还将研究各种维生素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、骨矿物质密度和福尔斯的影响，并构成我们的次要结局指标。我们希望这项建议的结果将增加关于更容易患骨质疏松症的绝经后妇女维生素D 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的工作来确定维生素D的RDA。这项研究的结果也将有助于设计未来更大规模的维生素D对福尔斯和骨折影响的临床试验。

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.