Why We Love Vitamin A
Friday, June 17, 2016
Today's Friday Pearl may sound a bit like claiming a favorite child, but vitamin A truly is one of our most favorite vitamins. It’s the essential, fat-soluble nutrient that the body stores mostly in the liver to be released into the blood stream whenever needed. The human body cannot make vitamin A—we can only obtain it from external sources.
Dietary vitamin A comes in two forms:
1. Preformed vitamin A retinol is naturally present in milk fat, animal livers, fish-liver oil and breast milk. It's converted by the body to retinyl esters for liver storage.
2. Proformed vitamin A from nonpolar, hydro-carbon plant-based carotenoids like beta carotene are metabolically converted to vitamin A retinyl esters, but only if and when the body's liver stores are deficient in preformed vitamin A.
The macula pigment xanthophyll carotenoids, lutein and zeaxanthin, have no ability to convert to vitamin A retinyl esters, so they are not appropriate as a beta carotene vitamin A substitute in formulations designed for ocular health.
Why does everyone need vitamin A?
Vitamin A supports vision and eye health at every age as well as an entire host of other cellular structure / function jobs including gene transcription, immune system function, bone metabolism, skin and cellular health, antioxidant activity, sperm cell formation and development of the central nervous system.
Our bodies store extra vitamin A in our livers so that we have the vitamin A reserve we need for the many cellular structure / functions that it facilitates daily throughout our entire life.
The role of vitamin A in the visual cycle is specifically related to the retinal form. Within the eye, retinal is bound to the protein opsin to form rhodopsin in rods and iodopsin in cones, which supports dark adaptation throughout life and makes safe night driving possible, particularly as we age and still see just fine when there is plenty of light—but not so well at night.
Vitamin A deficiency is reported by the World Health Organization to affect an estimated 190 million preschool-age children and 19 million pregnant women around the world. It’s one of the major contributors to infant and child mortality.
Because vitamin A is stored in the liver, supplementation is a low-cost and highly effective way to support the vitamin A status of vulnerable children and adults.
Global efforts to support national governments in addressing vitamin A deficiency are led by the Global Alliance for Vitamin A (GAVA), which is an informal partnership between the Canadian International Development Agency, Helen Keller International, the Micronutrient Initiative, UNICEF, USAIS and the World Bank. A meta-analysis of 43 studies showed that vitamin A supplementation of children under age five who are at risk of deficiency reduces mortality by up to 24 percent.
The World Health Organization estimates that Vitamin A supplementation has averted more than a million deaths due to vitamin A deficiency in 40 countries since 1998.
Vitamin A toxicity
Because vitamin A as retinol is fat-soluble, this allows for toxic levels to accumulate. In general, 2,500 to 5,000 international units (IU) of supplemental vitamin A retinol per day are well within the safety range according to FDA dietary supplement amount per serving % daily value label requirements. The Institute of Medicine determines 10,000 IU per day to be the safe upper limit (UL) for long-term daily dosage for adults.
Ellen Troyer, with Spencer Thornton, MD, and the Biosyntrx staff.
A reminder: Last week's Friday Pearl discussed the science-supported reasons why it's not a good idea to choose ocular-focused supplements that include carotenes (alpha or beta carotene) as the vitamin A source because they compete with the macula pigment carotenoids (lutein and zeaxanthin) for lipoprotein transport space.
Our Friday Pearl supporting bibliographic citations are no longer available on our website.This is to meet FDA-monitored federal government regulations that prevent supplement companies from using educational peer-reviewed science from the U.S. National Institutes of Health National Library of Medicine to encourage eye and body health. The citations are available for healthcare professionals in the Biosyntrx office.
If you view this as a possible government "Freedom of Information Act" issue, we recommend graciously contacting your elected state representatives and voicing your concern.
Doi-Uematsu Intravitreal Injection Guide Forceps 9-554-3
Clinical references available in the Biosyntrx office.