Vitamins
John K. DiBaise, Carol Rees Parrish, Jon S. Thompson in Short Bowel Syndrome Practical Approach to Management, 2017
Vitamin A (retinol) is necessary for vision, bone growth, immune function, and differentiation of epithelial and nerve tissues [1]. It can also reverse the negative effects of corticosteroids on wound healing [11]. Clinical signs of vitamin A deficiency, such as night blindness, are listed in Table 12.2. Dietary vitamin A is consumed in the form of retinol or provitamin A (carotenoids, mainly β-carotene). When consumed as part of the diet, vitamin A is liberated from food by pancreatic and digestive enzymes, incorporated into micelles, and then absorbed by enterocytes. After absorption and incorporation into chylomicrons, vitamin A is transported through the lymphatics to the liver, where it is transferred to retinol binding protein (RBP) and transthyretin. Protein-bound retinol is transported to target tissues, and any excess is stored in the liver (main site), adipose tissue, eyes, lungs, and kidneys [1].
Vitamin A
Judy A. Driskell, Ira Wolinsky in Sports Nutrition, 2005
Vitamin A constitutes a vital part of our visual system.2 Photoreceptors of the retina in the eye (rods) contain rhodopsin, a photo-sensitive pigment composed of 11-cis-retinal and a protein, opsin. Visual impulse is produced when 11-cis-retinal absorbs a photon, changes to all-trans-retinal, and disengages from opsin. For continuous vision, rhodopsin must be regenerated by isomerization of all-trans-retinol to 11-cis-retinol and the oxidation of the latter to 11-cis-retinal. These reactions proceed in retinal pigment epithelium (RPE), which contains a local pool of retinyl esters and the specific enzymes. The visual cycle continues because 11-cis-retinal is transported back to the rods to combine with opsin. The first symptom of vitamin A deficiency is an impaired dark adaptation, which develops into night blindness.
History of public health in Pacific Island countries
Milton J. Lewis, Kerrie L. MacPherson in Public Health in Asia and the Pacific, 2007
While coastal life on the high islands can be something like ‘subsistence affluence’ (Fisk 1982: 1–12; Sahlins 1972), human habitation on atolls, especially near the equator, requires fortitude and considerable ingenuity. Atolls are indeed desert islands where few food-producing plants besides coconut and pandanus grow naturally. Root crops are grown in pits dug down to the water table and fed by mulching; these giant taro take years to grow and are harvested and eaten on ceremonial occasions, much like pigs in the PNG highlands. South American plants such as papaya did not reach atoll countries until taken there as food plants by European colonizers. Lack of green leafy vegetables and yellow/orange fruits lead to vitamin A deficiency causing increased susceptibility to infection, especially in children, and night blindness and eye disease. A previous focus on explicit signs of eye disease (xeropthalmia) as indicative of clinical vitamin A deficiency masked the more widespread effects of infection and death due to subclinical deficiency. When looked for, significant vitamin A deficiency has been found in several Pacific Island countries, especially the atoll countries of Kiribati and the Marshall Islands (Anonymous 2001: 667–668; Schaumberg et al. 1995: 311–317), and may well partly explain some of the infant and childhood mortality found there.
Differential effect of a carotenoid-rich diet on retina function in non-diabetic and diabetic rats
Published in Nutritional Neuroscience, 2020
Kathleen J. McClinton, Michel Aliani, Sharee Kuny, Yves Sauvé, Miyoung Suh
Carrots, a well-known health food for the eyes, are one of the richest sources of β-carotene and α-carotene.1,2 Carotenoids are essential for retina function, as precursors of vitamin A, the very substrate of the only chromophore of photoreceptors (rods and cones), 11-cis retinal.3 The aldehyde form of vitamin A (11-cis retinal), converted solely from the diet, covalently binds to the photopigment opsin, and initiate phototransduction cascade when photoisomerized from cis to trans in response to photon catch.4 While 11-cis retinal is recycled by the retina, a continuous supply remains essential for the first steps of vision. Vitamin A deficiency can cause night blindness if sustained.5 Numerous studies have examined the role of supplementation of purified vitamin A, and β-carotene respectively on healthy vision and visual disorders; however, the impact of a whole food containing several carotenoids has been never tested.
RIP140/PGC-1α axis involved in vitamin A-induced neural differentiation by increasing mitochondrial function
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2018
Qing Mu, Weidong Yu, Shuying Zheng, Hongxia Shi, Mei Li, Jie Sun, Di Wang, Xiaoli Hou, Ling Liu, Xinjuan Wang, Zhuran Zhao, Rong Liang, Xue Zhang, Wei Dong, Chaomei Zeng, Jingzhu Guo
Natural derivatives of vitamin A, retinoids such as 9-cis-retinoic acid (9-cis-RA), 13-cis-retinoic acid (13-cis-RA), and all-trans-retinoic acid (at-RA), play important roles in neural differentiation [7,8]. RAs act as the ligand for nuclear retinoic acid receptors (RARs) and retinoid X receptors (RXRs), regulating gene expression by binding to short DNA sequences in the upstream promoter elements of target genes [9]. RARs can be activated by both at-RA and 9-cis-RA, whereas RXRs are only activated by 9-cis-RA. RARs and RXRs both consist of α, β, and γ-subtypes [10]. Endogenous neuronal RA synthesis occurs in the hippocampus, where RARα is strongly expressed [3]. Vitamin A exert its function in the body by its derivatives, both vitamin A and its derivatives can be exogenously added by diet or drug, which can be used as a therapeutic strategy for vitamin A deficiency-related disorders.
Role of Vitamin B12 and Vitamin D levels in intrahepatic cholestasis of pregnancy and correlation with total bile acid
Published in Journal of Obstetrics and Gynaecology, 2022
Sebahattin Celik, Hakan Golbasi, Selim Gulucu, Mehmet Guclu, Canan Soyer Caliskan, Samettin Celik, Yasam Kemal Akpak, Ceren Golbasi
Vitamin D affects hepatobiliary hemostasis and is involved in bile acid detoxification (Zollner and Trauner 2009). Furthermore, many studies have shown that Vitamin D deficiency is associated with primary biliary cirrhosis (Guo et al. 2015), fatty liver disease (Kwok et al. 2013), chronic hepatitis B (Farnik et al. 2013), and chronic hepatitis C (Petta et al. 2010). Few studies in the literature have evaluated the association between Vitamin D and ICP. In the study by Gençosmanoğlu Türkmen (2018) involving 40 ICP cases, plasma Vitamin D levels were lower than the control group, and there was a negative correlation between disease severity and Vitamin D levels. In the study by Kuoppala et al. (1986) with 22 ICP cases, plasma Vitamin D levels were low in the ICP group, and the plasma level continued to decrease until delivery, whereas in the healthy group, no decrease was observed in the Vitamin D level until delivery. In the study by Shemer et al. with 22 ICP cases, Vitamin D plasma levels were significantly lower than the control group (Wikstrom Shemer and Marschall 2010). In these studies, conducted with a small number of cases, low Vitamin D levels were associated with ICP. In our study, which included 92 ICP cases, Vitamin D levels in the ICP group were significantly lower than those in the control group, similar to previous studies, and there was a moderate negative correlation between Vitamin D levels and TBA.
Related Knowledge Centers
- Childhood Blindness
- Nyctalopia
- Tissue
- Vitamin A
- Xerophthalmia
- Blood
- Pregnancy
- Visual Phototransduction
- Keratomalacia
- Maternal Death