Zita West Vitamen - Ultimate Male Fertility Supplement - 30 Capsules (1 Months Supply)

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The US National Academy of Medicine updated Dietary Reference Intakes (DRIs) in 2001 for vitamin A, which included Recommended Dietary Allowances (RDAs). [4] For infants up to 12 months there was not sufficient information to establish a RDA, so Adequate Intake (AI) is shown instead. As for safety, tolerable upper intake levels (ULs) were also established. For ULs, carotenoids are not added when calculating total vitamin A intake for safety assessments. [4] Life stage group Publishing, Harvard Health (9 June 2009). "Listing of vitamins". Harvard Health . Retrieved 12 May 2020.

Retinyl esters from animal-sourced foods (or synthesized for dietary supplements for humans and domesticated animals) are acted upon by retinyl ester hydrolases in the lumen of the small intestine to release free retinol. Retinol enters intestinal absorptive cells by passive diffusion. Absorption efficiency is in the range of 70 to 90%. Humans are at risk for acute or chronic vitamin A toxicity because there are no mechanisms to suppress absorption or excrete the excess in urine. [4] Within the cell, retinol is there bound to retinol binding protein 2 (RBP2). It is then enzymatically reesterified by the action of lecithin retinol acyltransferase and incorporated into chylomicrons that are secreted into the lymphatic system. a b c Bono MR, Tejon G, Flores-Santibañez F, Fernandez D, Rosemblatt M, Sauma D (June 2016). "Retinoic Acid as a Modulator of T Cell Immunity". Nutrients. 8 (6): 349. doi: 10.3390/nu8060349. PMC 4924190. PMID 27304965. Stipanuk MH (2006). Biochemical, Physiological and Molecular Aspects of Human Nutrition (2nded.). Philadelphia: Saunders. ISBN 9781416002093. As some carotenoids can be converted into vitamin A, attempts have been made to determine how much of them in the diet is equivalent to a particular amount of retinol, so that comparisons can be made of the benefit of different foods. The situation can be confusing because the accepted equivalences have changed over timeRoth KS (September 1981). "Biotin in clinical medicine--a review". The American Journal of Clinical Nutrition. 34 (9): 1967–74. doi: 10.1093/ajcn/34.9.1967. PMID 6116428. a b Wirth JP, Petry N, Tanumihardjo SA, Rogers LM, McLean E, Greig A, etal. (February 2017). "Vitamin A Supplementation Programs and Country-Level Evidence of Vitamin A Deficiency". Nutrients. 9 (3): 190. doi: 10.3390/nu9030190. PMC 5372853. PMID 28245571. Maharshak N, Shapiro J, Trau H (March 2003). "Carotenoderma--a review of the current literature". International Journal of Dermatology. 42 (3): 178–181. doi: 10.1046/j.1365-4362.2003.01657.x. PMID 12653910. S2CID 27934066. Hardman, J.G.; etal., eds. (2001). Goodman and Gilman's Pharmacological Basis of Therapeutics (10thed.). McGraw-Hill. p.992. ISBN 978-0071354691. Akhtar S, Ahmed A, Randhawa MA, Atukorala S, Arlappa N, Ismail T, Ali Z (December 2013). "Prevalence of vitamin A deficiency in South Asia: causes, outcomes, and possible remedies". Journal of Health, Population, and Nutrition. 31 (4): 413–423. doi: 10.3329/jhpn.v31i4.19975. PMC 3905635. PMID 24592582.

Wang S, Moise AR (July 2019). "Recent insights on the role and regulation of retinoic acid signaling during epicardial development". Genesis. 57 (7–8): e23303. doi: 10.1002/dvg.23303. PMC 6682438. PMID 31066193. Welch AD (1983). "Folic acid: discovery and the exciting first decade". Perspect. Biol. Med. 27 (1): 64–75. doi: 10.1353/pbm.1983.0006. PMID 6359053. S2CID 31993927.a b "Vitamin A". The American Society of Health-System Pharmacists. Archived from the original on 30 December 2016 . Retrieved 8 December 2016. a b c d e f g h "Vitamin A". Micronutrient Information Center, Linus Pauling Institute, Oregon State University, Corvallis. 1 July 2016 . Retrieved 21 December 2021. Vitamin A Supplementation: A Decade of Progress (PDF). New York: UNICEF. 2007. p.3. ISBN 978-92-806-4150-9. Archived from the original (PDF) on 31 October 2020 . Retrieved 23 January 2011. Since vitamin A is fat-soluble, it is more efficiently absorbed into the bloodstream when eaten with fat. Most animal-sourced foods that are rich in vitamin A are also high in fat, but the same doesn’t apply to most plant sources of provitamin A. Cañete A, Cano E, Muñoz-Chápuli R, Carmona R (February 2017). "Role of Vitamin A/Retinoic Acid in Regulation of Embryonic and Adult Hematopoiesis". Nutrients. 9 (2): 159. doi: 10.3390/nu9020159. PMC 5331590. PMID 28230720.