Vitamin D insufficiency: Prevalence and Impact in Young School Age Children

描述（由申请人提供）：维生素D不足被认为是居住在美国的健康成年人和青少年中未被认识到的流行病。流行病学和临床数据清楚地表明，成人和青少年中维生素D缺乏的患病率很高。然而，对于青少年前期和早期儿童人群中维生素D不足的患病率、季节性变化和代谢影响知之甚少。采用纵向研究设计，我们将估计6至12岁青春期前和早期儿童维生素D不足的患病率和季节性变化，并表征其对骨骼健康的代谢影响。根据计算的样本量估计，将在夏季（6月至9月）和冬季（12月至3月）对140名健康的青春期前和早期儿童（6-12岁，Tanner I或II，非裔美国人[n=94]和高加索人[n=46]）进行评估。在夏季和冬季将评估维生素D状况、钙化激素和骨转换标志物。收集的其他数据还包括膳食中维生素D和钙的摄入量、日晒量和体重指数。维生素D不足将定义为血清25羟维生素D < 20 ng/mL，但根据血清25羟维生素D与甲状旁腺激素的关系，确定维生素D充足所需的血清25羟维生素D阈值水平。本研究将确定非裔美国人和白种人学龄儿童维生素D缺乏的患病率、季节性变化和代谢影响。儿童维生素D不足对公共卫生的重要性与维生素D水平对骨量峰值获得的影响有关。骨量峰值降低会导致骨质疏松症和骨质疏松性脆性骨折的过早发作。儿童期维生素D不足的治疗和预防将对儿童的骨骼健康产生积极影响，并减少成年期的“骨质疏松症负担”。由于缺乏与学龄儿童维生素D充足状态相关的阈值维生素D水平的数据，以及非裔美国人和高加索儿童之间维生素D充足所必需的血清25羟维生素D阈值可能不同的潜在可能性，使得这个问题值得探讨。

DESCRIPTION (provided by applicant): Vitamin D insufficiency is deemed as an unrecognized epidemic among healthy adults and adolescents residing in the United States. Epidemiologic and clinical data clearly document the high prevalence of vitamin D insufficiency among adults and adolescents. However very little is known regarding the prevalence, seasonal variation and the metabolic impact of vitamin D insufficiency among pre- and early adolescent childhood populations. Using a longitudinal study design, we will estimate the prevalence and seasonal variation of vitamin D insufficiency in 6 to 12 year old pre- and early adolescent children and characterize its metabolic impact on their skeletal health. On the basis of the calculated sample size estimate, a cohort of 140 healthy pre- and early adolescent children (6-12 year old, Tanner I or II, African American [n=94] and Caucasian [n=46]) will be evaluated during summer (June through September) and winter (December through March). Vitamin D status, calcitrophic hormones, and markers of bone turnover will be assessed during summer and winter. Other measures collected will include dietary intakes of vitamin D and calcium, sun exposure and body mass index. Vitamin D insufficiency will be defined as serum 25 hydroxyvitamin D < 20 ng/mL However, on the basis of the relationship between serum 25 hydroxyvitamin D and PTH, the threshold level of serum 25 hydroxyvitamin D essential for vitamin D sufficiency will be determined. This study will establish the prevalence, seasonal variation, and the metabolic impact of vitamin D insufficiency in young school age African American and Caucasian children. The public health importance of childhood vitamin D insufficiency is linked to the impact of vitamin D status on the acquisition of peak bone mass. Reduced peak bone mass will predispose to premature onset of osteoporosis and osteoporotic fragility fractures. Treatment and prevention of vitamin D insufficiency during childhood will positively impact the skeletal health of children and reduce the "osteoporosis burden" during adulthood. The paucity of data regarding threshold vitamin D levels associated with vitamin D sufficiency status among young school age children and the potential likelihood that the threshold serum 25 hydroxyvitamin D levels essential for vitamin D sufficiency could be different between African American and Caucasian children, makes it compelling for this issue to be explored.