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Vitamin A plays a vital role in vision, differentiation of epithelial cells (cells lining the skin and body passages), growth, reproduction, bone and brain development and hematopoiesis (formation of red cells). Vitamin A is also variously referred to as retinol (on the basis of the parent substance of the group) or retinoid (on the basis of its metabolites and derivatives). Beta-Carotene is converted in the body to Vitamin A. Deficiency may cause night blindness, and affect the epithelia of the body passages. Vitamin A confers immunity. Retinoids are known to inhibit or reverse cancers. Rich sources of vitamin A are liver, fish liver oils, and egg yolks. Recommended daily allowance is 5000 IU/day. (For more detailed information, please visit ISM’s searchable database: Nutraceutical Search.)
Retinoids (i.e., vitamin A, all-trans retinoic acid, and related signaling molecules) induce the differentiation of various types of stem cells………..Retinoid signaling is often compromised early in carcinogenesis [the process of cancer development], which suggests that a reduction in retinoid signaling may be required for tumor development. …… Thus, retinoid research benefits both cancer prevention and cancer treatment.
o o Tang, XH & Gudas, LJ (2011). Retinoids, retinoic acid receptors, and cancer. Annu Rev Pathol. 28(6), 345-64.
Retinoids are ubiquitous signaling molecules that influence nearly every cell type, exert profound effects on development, and complement cancer chemotherapeutic regimens. All-trans retinoic acid (RA) and other active retinoids are generated from vitamin A (retinol)………… In cancer chemotherapeutic regimens retinoids can promote tumor cell differentiation and/or induce proteins that sensitize tumors to drug combinations.
o Gudas, LJ & Wagner, JA (2011). Retinoids regulate stem cell differentiation. J Cell Physiol. 226(2), 322-30.
All-trans retinoic acid (ATRA) is an active metabolite of vitamin A under the family retinoid. Retinoids…….. exert potent effects on cell growth, differentiation and apoptosis [cell death], and have significant promise for cancer therapy and chemoprevention……….ATRA is being increasingly included in anti-tumour therapeutical schemes for the treatment of various tumoral diseases such as Kaposi's sarcoma, head and neck squamous cell carcinoma, ovarian carcinoma, bladder cancer, neuroblastoma.
o Siddikuzzaman, Guruvayoorappan, C, & Berlin Grace, VM (2010). All Trans Retinoic Acid and Cancer. Immunopharmacol Immunotoxicol. [Epub ahead of print]
Retinoids are prime candidates for cancer chemoprevention since cancer is characterized by abnormal growth with a lack of differentiation, which could be modified by retinoids………A number of experimental and clinical studies have been performed in the past two decades with retinoids showing that they inhibit or reverse the carcinogenic process in some organs, including hematological malignancy as well as premalignant and malignant lesions in the oral cavity, head and neck, breast, skin and liver.
o Okuno, M et al (2004). Retinoids in cancer chemoprevention. Curr Cancer Drug Targets, 4(3), 285-98.
Retinoids, which include vitamin A (retinol; ROL) and its derivatives, have been investigated in the treatment of bladder cancer. We have shown that expression of the enzyme lecithin: ROL acyltransferase (LRAT), which converts ROL to retinyl esters, is reduced in several human cancers. These data suggest that loss of LRAT expression is associated with invasive bladder cancer.
o Clin Cancer Res. 2004 May 15; 10(10): 3429-37.
High prediagnostic serum level of retinol is associated with a decreased risk of heptocelluar Carcinoma.
o J Natl Cancer Inst. 2006 Apr 5; 98(7): 482-90.
Derivatives of vitamin A, the retinoids, have reported activity in treating specific premalignant lesions and reducing incidence of second primary tumors in patients with prior head and neck, lung or liver cancers.
o Oncologist. 2000; 5(5): 361-8.
Epidemiological evidence shows an association between high dietary intake of vitamin A and a reduced risk of breast cancer among premenopausal women with a positive family history of breast cancer.
o Zhang, J Natl Cancer Inst (1999);91:547-56.
Vitamin A may improve survival and reduce the reoccurrence of tumors in people with lung cancer.
o Pastorino, J Clin Oncol (1993);11:1216-22.
The metabolism of vitamin A to retinyl esters is carried out primarily by the enzyme LRAT. LRAT protein expression was lost in prostate cancer. These data implicate aberrant retinoid metabolism in the process of prostatic carcinogenesis.
o Cancer Res. 2002 Mar 15; 62(6): 1654-61.
Background: Vitamin A may influence gastric carcinogenesis through its essential role in controlling cell proliferation and differentiation……….
Objective: The objective of the study was to examine the associations between intakes of vitamin A, retinol, and specific carotenoids and the risk of gastric cancer……..
Conclusion: High intakes of vitamin A, retinol, and provitamin A carotenoids may reduce the risk of gastric cancer.
o Larsson, SC et al (2007). Vitamin A, retinol, and carotenoids and the risk of gastric cancer: a prospective cohort study. Am J Clin Nutr. 85(2), 497-503.
Vitamin A has been long associated with immune system competence. Vitamin A deficiency is known to compromise many aspects of both innate and adaptive immune responses. Recent advances in retinol uptake and metabolism have identified the antigen presenting cell (APC) as a central immune cell capable of vitamin A metabolism………Previously, the focus of vitamin A action in adaptive immunity was on lymphocytes, but these recent advances suggest the APC may be the central player in carrying out the immune system functions of vitamin A.
o Duriancik, DM, Lackey, DE & Hoag, KA (2010). Vitamin A as a regulator of antigen presenting cells. J Nutr. 140(8), 1395-9.
Since there is a reported interrelationship between vitamin A and Fe metabolism, and with immunological response, the objective was to evaluate the effect of a single dose of vitamin A administered to preschool children, on Fe and vitamin A nutritional status, anaemia and phagocytic function of neutrophils, 30 d after supplementation……….A single dose of 200,000 IU (60 mg) vitamin A ……. enhanced serum retinol and Hb concentrations, decreased the prevalence of anaemia and vitamin A deficiency and improved the constitutive phagocytic capacity of neutrophils [white blood cells that kill and remove micro-organisms].
o o Jimenez, C et al (2010). A single dose of vitamin A improves haemoglobin concentration, retinol status and phagocytic function of neutrophils in preschool children. Br J Nutr. 103(6), 798-802.
Retinoids are vitamin A derivatives that critically regulate several physiological and pathological processes, including immune functions and cancer development…….Evidence has been accumulated indicating that retinoids may exert beneficial effects in both immune-mediated disorders and tumors. With regard to cancer, retinoids directly target neoplastic cells by inducing differentiation, inhibiting cell growth or promoting survival.
o o Montrone, M, Martorelli, D, Rosato, A & Dolcetti, R (2009). Retinoids as critical modulators of immune functions: new therapeutic perspectives for old compounds. Endocr Metab Immune Disord Drug Targets. 9(2),113-31.
Vitamin A supplementation to preschool children is known to decrease the risks of mortality and morbidity from some forms of diarrhea, measles, human immunodeficiency virus (HIV) infection, and malaria. These effects are likely to be the result of the actions of vitamin A on immunity.
o o Villamor, E & Fawzi, WW (2005). Effects of vitamin a supplementation on immune responses and correlation with clinical outcomes. Clin Microbiol Rev. 18(3), 446-64.
Vitamin A also has a role as an anti-inflammatory agent. Supplementation with vitamin A has been found to be beneficial in a number of inflammatory conditions, including skin disorders such as acne vulgaris, broncho-pulmonary dysplasia and some forms of precancerous and cancer states………The two main mechanisms which appear to be involved in the prevention of disease are the effects of vitamin A on the immune system and the effect on epithelial integrity.
o o Reifen, R (2002). Vitamin A as an anti-inflammatory agent. Proc Nutr Soc. 61(3), 397-400.
In populations where vitamin A availability from food is low, infectious diseases can precipitate vitamin A deficiency……..Vitamin A is also required for adaptive immunity and plays a role in the development of T both-helper (Th) cells and B-cells. In particular, vitamin A deficiency diminishes antibody-mediated responses directed by Th2 cells, although some aspects of Th1-mediated immunity are also diminished.
o o Stephensen, CB (2001). Vitamin A, infection, and immune function. Annu Rev Nutr. 21,167-92.