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

描述(申请人提供)：骨质疏松症在美国的患病率很高，约有1000万50岁以上的人已经患有这种疾病，另有3400万人面临发展为骨质疏松症的风险。首份以骨骼健康为主题的卫生局局长报告的发布强调了这一公共健康问题的严重性。开发低成本和有效的策略对于预防骨质疏松和减少骨质疏松性骨折具有重要意义。预防骨质疏松症的一个简单而廉价的策略是充足的钙和维生素D营养，血清25OHD现在被认为是维生素D营养的客观衡量标准。人们越来越多地认识到，血清25-羟基维生素D(25OHD)浓度至少需要30-32 ng/ml才能使血清甲状旁腺激素(PTH)浓度达到最低，从而实现最佳的骨骼健康。没有系统的前瞻性剂量反应研究旨在确定维持人群最佳血清25OHD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的估计平均需要量(EAR)和推荐膳食需要量(RDA)。拟议的建议旨在通过集中于60-85岁之间的绝经后女性高危群体来填补这一缺口。我们假设，在服用维生素D补充剂的研究对象中，97%的人在冬季将血清25OHD水平提高到30 ng/ml或更高，在钙摄入量充足的情况下，维生素D不足(血清25OHD和20 ng/ml)的高危人群的血清PTH水平将降低。我们推测，在97%的受试者中，达到血清25OHD-GT；30 ng/ml的维生素D剂量约为4400IU/天，远高于老年人推荐的400-600ID的适当维生素D摄入量。在为期一年的随机双盲前瞻性临床试验中，我们将检测冬季补充不同剂量维生素D3对绝经后维生素D缺乏的高加索和非裔美国妇女血清25OHD和PTH的剂量反应效应。此外，补充不同剂量的维生素D3对钙吸收、1，25-二羟基维生素D水平、血清钙、骨标记物、骨密度和跌倒的影响也将被研究，并成为我们的次要结果指标。我们希望这项建议的结果将增加有关绝经后妇女更易患骨质疏松症的维生素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维生素D对跌倒和骨折的影响的更大规模的临床试验。

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.