Gallagher J Christopher, Jindal Prachi S, Smith Lynette M
Bone Metabolism Unit, Creighton University Medical Center, Omaha, NE, USA.
J Bone Miner Res. 2014;29(5):1081-7. doi: 10.1002/jbmr.2121.
It is commonly said that vitamin D should be used to increase calcium absorption. We tested this statement in a dose-response study of vitamin D on calcium absorption. A total of 198 white and African American women, aged 25 to 45 years, with vitamin D insufficiency, serum 25-hydroxyvitamin D (25OHD) <20 ng/mL, were randomized in a double-blind study to vitamin D3 400, 800, 1600, 2400 IU, or placebo. A calcium supplement was given to increase mean calcium intake at baseline from 706 mg/d to 1031 mg/d. Calcium absorption was measured at baseline and after 12 months using a single isotope method with radiocalcium45 and 100 mg of calcium. Mean baseline serum 25OHD was 13.4 ng/mL (33.5 nmol/L) and increased to 40 ng/mL (100 nmol/L) on the highest dose of 2400 IU. Using a multivariate regression analysis with significant predictors, baseline absorption, calcium intake, and weight, there was no increase in 12-month calcium absorption compared with baseline on any dose of vitamin D in either whites or African Americans. There was no significant relationship between 12-month calcium absorption and final serum 25OHD. In an analysis of calcium absorption and serum 25OHD at baseline, serum 25OHD levels were divided into groups: 0 to 5, 6 to 10, 11 to 15, or 16 to 20 ng/mL. There was no evidence of a threshold decrease in calcium absorption or serum 1,25 dihydroxyvitamin D (1,25(OH)2 D) amongst the lowest groups. Vitamin D doses up to 2400 IU daily did not increase calcium absorption. No threshold level of serum 25OHD for calcium absorption was found at baseline or in the longitudinal study, suggesting that active transport of calcium is saturated at very low serum 25OHD levels <5 ng/mL. There is no need to recommend vitamin D for increasing calcium absorption in normal subjects. Very efficient calcium absorption at very low levels of serum 25OHD explains why people do not develop osteomalacia provided that dietary intakes of calcium and phosphorus are adequate.
人们普遍认为维生素D可用于增加钙的吸收。我们在一项关于维生素D对钙吸收的剂量反应研究中对这一说法进行了测试。共有198名年龄在25至45岁之间、维生素D不足（血清25-羟基维生素D（25OHD）<20 ng/mL）的白人和非裔美国女性，在一项双盲研究中被随机分为接受400、800、1600、2400 IU的维生素D3或安慰剂组。给予钙补充剂，以使基线时的平均钙摄入量从706 mg/d增加到1031 mg/d。在基线时和12个月后，使用放射性钙45和100 mg钙的单同位素方法测量钙吸收情况。平均基线血清25OHD为13.4 ng/mL（33.5 nmol/L），在2400 IU的最高剂量下增加到40 ng/mL（100 nmol/L）。在对具有显著预测因素（基线吸收、钙摄入量和体重）的多变量回归分析中，无论是白人还是非裔美国人，任何剂量的维生素D在12个月时的钙吸收与基线相比均未增加。12个月时的钙吸收与最终血清25OHD之间没有显著关系。在对基线时的钙吸收和血清25OHD进行分析时，血清25OHD水平被分为几组：0至5、6至10、11至15或16至20 ng/mL。在最低组中没有证据表明钙吸收或血清1,25-二羟基维生素D（1,25(OH)2D）有阈值降低。每日高达2400 IU的维生素D剂量并未增加钙吸收。在基线或纵向研究中均未发现钙吸收的血清25OHD阈值水平，这表明在血清25OHD水平非常低<5 ng/mL时钙的主动转运已饱和。在正常受试者中无需推荐使用维生素D来增加钙吸收。在血清25OHD水平非常低时非常高效的钙吸收解释了为什么只要钙和磷的膳食摄入量充足，人们就不会患骨软化症。
