Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA.
J Lipid Res. 2013 Jul;54(7):1731-43. doi: 10.1194/jlr.R037648. Epub 2013 Apr 26.
By definition, a vitamin is a substance that must be obtained regularly from the diet. Vitamin A must be acquired from the diet, but unlike most vitamins, it can also be stored within the body in relatively high levels. For humans living in developed nations or animals living in present-day vivariums, stored vitamin A concentrations can become relatively high, reaching levels that can protect against the adverse effects of insufficient vitamin A dietary intake for six months, or even much longer. The ability to accumulate vitamin A stores lessens the need for routinely consuming vitamin A in the diet, and this provides a selective advantage to the organism. The molecular processes that underlie this selective advantage include efficient mechanisms to acquire vitamin A from the diet, efficient and overlapping mechanisms for the transport of vitamin A in the circulation, a specific mechanism allowing for vitamin A storage, and a mechanism for mobilizing vitamin A from these stores in response to tissue needs. These processes are considered in this review.
根据定义，维生素是一种必须定期从饮食中获取的物质。维生素 A 必须从饮食中获得，但与大多数维生素不同，它也可以在体内以相对较高的水平储存。对于生活在发达国家的人类或生活在现代动物园中的动物来说，储存的维生素 A 浓度可能会变得相对较高，达到可以保护身体免受六个月甚至更长时间维生素 A 饮食摄入不足的不良影响的水平。积累维生素 A 储存的能力降低了饮食中常规摄入维生素 A 的必要性，这为生物体提供了选择性优势。这种选择性优势的基础分子过程包括从饮食中获取维生素 A 的有效机制、维生素 A 在血液循环中的运输的高效和重叠机制、允许维生素 A 储存的特定机制以及一种用于根据组织需要从这些储存中动员维生素 A 的机制。本综述考虑了这些过程。
