Department of Surgery, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
The Tennessee Valley Nashville VA Medical Center, Nashville, Tennessee, USA.
Nutr Clin Pract. 2019 Oct;34(5):695-700. doi: 10.1002/ncp.10376. Epub 2019 Aug 7.
Vitamin A is an essential micronutrient that comes in multiple forms, including retinols, retinals, and retinoic acids. Dietary vitamin A is absorbed as retinol from preformed retinoids or as pro-vitamin A carotenoids that are converted into retinol in the enterocyte. These are then delivered to the liver for storage via chylomicrons and later released into the circulation and to its biologically active tissues bound to retinol-binding protein. Vitamin A is a crucial component of many important and diverse biological functions, including reproduction, embryological development, cellular differentiation, growth, immunity, and vision. Vitamin A functions mostly through nuclear retinoic acid receptors, retinoid X receptors, and peroxisome proliferator-activated receptors. Retinoids regulate the growth and differentiation of many cell types within skin, and its deficiency leads to abnormal epithelial keratinization. In wounded tissue, vitamin A stimulates epidermal turnover, increases the rate of re-epithelialization, and restores epithelial structure. Retinoids have the unique ability to reverse the inhibitory effects of anti-inflammatory steroids on wound healing. In addition to its role in the inflammatory phase of wound healing, retinoic acid has been demonstrated to enhance production of extracellular matrix components such as collagen type I and fibronectin, increase proliferation of keratinocytes and fibroblasts, and decrease levels of degrading matrix metalloproteinases.
维生素 A 是一种必需的微量营养素，有多种形式，包括视黄醇、视黄醛和视黄酸。膳食中的维生素 A 以视黄醇的形式从预先形成的类视黄醇中吸收，或以视黄醇原类胡萝卜素的形式吸收，后者在肠细胞中转化为视黄醇。这些随后通过乳糜微粒被递送至肝脏储存，然后释放到循环中，并与视黄醇结合蛋白结合进入其具有生物活性的组织。维生素 A 是许多重要和多样化的生物学功能的关键组成部分，包括生殖、胚胎发育、细胞分化、生长、免疫和视力。维生素 A 主要通过核视黄酸受体、视黄醛 X 受体和过氧化物酶体增殖物激活受体发挥作用。类视黄醇调节皮肤内多种细胞类型的生长和分化，其缺乏会导致上皮角质化异常。在受伤组织中，维生素 A 刺激表皮更新，增加再上皮化的速度，并恢复上皮结构。类视黄醇具有独特的能力，可以逆转抗炎类固醇对伤口愈合的抑制作用。除了在伤口愈合的炎症阶段发挥作用外，已证明视黄酸还能增强细胞外基质成分（如 I 型胶原和纤维连接蛋白）的产生，增加角质形成细胞和成纤维细胞的增殖，并降低降解基质金属蛋白酶的水平。
