School of Population Health, The University of Auckland, Auckland, New Zealand.
J Steroid Biochem Mol Biol. 2018 Mar;177:6-9. doi: 10.1016/j.jsbmb.2017.06.006. Epub 2017 Jun 13.
Observational studies have shown that low vitamin D status is associated with an increased risk of a wide range of diseases. The body of observational evidence now is so large, that there have been many calls for randomized controlled trials (RCT) of vitamin D supplementation to confirm once and for all whether increasing body vitamin D levels prevents these diseases. These calls have arisen because of concern that confounding and reverse causation may explain many of the results from observational studies. However, RCTs also are prone to limitations that compromise their validity. These include low response rates that affect their external validity; and biases that affect their internal validity, such as recruitment of vitamin D sufficient people which decreases the power to detect beneficial effects, studies of long-term outcomes requiring participation for many years which decreases compliance and retention, and easy access for participants to vitamin D supplements and blood testing which increase contamination and unblinding. Because of these potential limitations, it is possible that RCTs of vitamin D supplementation may not to give a clear answer by themselves. Future decisions about the role of vitamin D in health are likely to be based on the evidence from a range of study designs including RCTs, mendelian randomization studies and other observational designs.
观察性研究表明，维生素 D 状态低下与多种疾病的风险增加有关。现在观察性证据如此之多，以至于人们多次呼吁进行维生素 D 补充的随机对照试验 (RCT)，以一劳永逸地确定增加体内维生素 D 水平是否可以预防这些疾病。之所以提出这些呼吁，是因为担心混杂和反向因果关系可能解释了许多观察性研究的结果。然而，RCT 也容易受到影响其有效性的限制。这些限制包括影响其外部有效性的低应答率；以及影响其内部有效性的偏倚，例如招募维生素 D 充足的人会降低检测有益效果的能力、需要多年参与的长期结局研究降低了依从性和保留率、以及参与者容易获得维生素 D 补充剂和血液检测增加了污染和揭盲。由于这些潜在的限制，维生素 D 补充 RCT 本身可能无法给出明确的答案。未来关于维生素 D 在健康中的作用的决策可能基于一系列研究设计的证据，包括 RCT、孟德尔随机化研究和其他观察性设计。
