Olivia Allen
Lauren Arnett
Allison Drury
Brett Leinweber
KNH 304 – Media Presentation
A is for more than just apple
Possibly some of the oldest known vitamins are part of the group known as
Vitamin A. Their physiological importance is so significant that many functions
would be impossible without their facilitation. Among the most well known roles of
Vitamin A is vision and immune support. The perceived benefit of Vitamin A has
lead to many supplementation products that provide amounts far exceeding the
amounts deemed necessary. Benefits of such mega doses are still unclear but
continue to be endorsed by research organizations, such as, the Linus Pauling
Institute.
It is estimated that knowledge of Vitamin A has existed for more than three
millennia, dating back to ancient Egypt (1). Evidence suggests that there was an
awareness of the correlation between night blindness and the deficiency of what is
now known to be vitamin A. Physicians would treat this condition by putting the
juices from the liver of a lamb over the eyes of those afflicted. It is believed that the
effectiveness of this treatment is due to the high concentration of retinol that is
contained in the live. The occurrence of night blindness continued into the 18th and
19th centuries, in which, patients were treated with cod oil (3).
In the early 20th century there was much research conducted that laid the
foundation for understanding dietary needs. Among these nutritional components
were deemed “vital amines”(2). Certain research led to a discovery of the link
between a compound found in dairy and cod liver that prevented night blindness
and many other afflictions. The compound was named “critical factor fat soluble A”.
In 1928, the immune properties of Vitamin A were identified when daily
administration to measles patients was shown to drastically reduce mortality.
Vitamin A was finally isolated in 1937.
“Vitamin A” is a generic term for a group of certain fat-soluble compounds. It
is found as preformed vitamin A and provitamin A. The preformed type includes
retinol and retinyl ester, which belong to the class of organic compounds known as
retinoids. Unlike preformed Vitamin A, provitamin A refers to organic compounds
that can be used by the body to synthesize vitamin A. The most significant of these
compounds is beta-carotene. Both types of vitamin A must be converted
intracellularly into the active forms, retinal and retinoic acid before they can be used.
Most is stored in the liver in the ester form(2).
Many physiological processes rely on the utilization of vitamin A. Its role in
vision is vital, as it is found in photoreceptor proteins. These proteins, known as
rhodopsin, undergo certain chemical reactions when exposed to light (4). Other
roles of Vitamin A include its immune properties, inflammatory system, maintaining
cellular growth for epithelial and mucosal tissues, reproduction, red blood cell
synthesis/development and bone development. Retinoic acid is believed to help
with the proliferation of T-cells and may regulate inflammatory responses (6). It
crucial to T cell and B cell synthesis, correctly respond and activate the immune
system in times of need. Retinoic acid also plays a strong role in glucoprotein
synthesis, allowing cells to attach to one another and recognize cells.
Vitamin A does possess some preventative connections or serve a treatment
option for some conditions. The retinoid and carotenoid forms of the vitamin can
help with acne, alcoholism, diabetes, osteoarthritis, viral infections, asthma, heart
disease, and several types of cancers (7). In terms of skin disorders such as acne and
psoriasis can be treated with a synthetic form of vitamin A. Often in the form of pills
or creams, this man made form can be helpful. Unfortunately it does come with a
cost and should be used only under a doctor’s supervision due to possible side
effects (10). Though not all correlations are explicitly mapped out and understood,
they are still noted and should be recognized. People who may be at risk for such
disease such be more aware of the intake of vitamin A and making sure they are
meeting the RDA decoding on their age, gender, etc.
Issues with Vitamin A function can cause major effects in the body. For
example, retinoid acid requires two enzymes in order to be synthesized in our cells.
It si believed that an issue with this linking of enzymes can cause a range of
problems in human growth and development (7). Issues in reproduction such as
undergoing proper spermatogenesis can also be attributed to Vitamin A. Research is
suggesting new links between retinoic acid and genetic events that could contribute
to problems with growth and development.
Dietary sources of the two types the two types of vitamin A differ. Significant
amounts of preformed vitamin A can be found predominately in animal products,
such as, liver and fish oil. It can also be found in dairy products and eggs. In contrast,
provitamin sources consist of mostly plants. Most significant sources of betacarotene are green leafy vegetables like spinach and broccoli (3). How these foods
are cooked, processed, and stored can have an affect on the amount of vitamin A
that remains available for the body to absorb. The Vitamin A that is added to milk
can be damaged by light. If milk is stored in an opaque container and remains in the
refrigerator then this issue is usually avoided. Cooking certain vegetables can be
beneficial to absorbing vitamin A. High carotenoid foods like carrots actually
become arranged with more cis forms thus making it more available to the
bloodstream. Cooked carrots were shown to allow for better carotenoid blood levels
in contrast to eating raw carrots (7).
As with many other essential nutrients, vitamin A deficiency is prevalent in
many developing countries. Malnutrition results in inadequate sources of preformed
and vitamin A and beta-carotene in these populations. A distinct sign of this
deficiency is night blindness, which is due to the lack of retinal presence in
photoreceptors. Prolonged deficiency may lead to permanent blindness. This
deficiency also has significant impacts on the immune system. This compromise of
immune function results in the increased susceptibility to infectious disease and
often death. Of the populations most at risk are infants, children, and pregnant
women (5). Even with the wide range of food sources and ability to supplement for
vitamin A, about one third of adults in the United States are still deficient (7).
The fat-soluble properties of Vitamin A make it possible to take in
detrimental amounts. Overdoes of the preformed type, specifically, can result in
toxicity. In contrast, provitamin A is only used to synthesize vitamin A when it is
needed by the body (4). It is because of this that sources of vitamin A are preferred
to be higher in beta-carotene. Toxicity of vitamin A is known as hypervitaminosis
(1). Chronic exposure to excessive amounts of preformed vitamin A can result in
mild symptoms, such as, loss of appetite, headache and joint pain. The most common
reason for toxicity is supplementation. In a study was published regarding the risk
of death from lung cancer and whether or not a combination supplement of vitamin
A and beta carotene had any effect. The results were surprising, showing a higher
mortality for those who received the supplement compared to those who did not.
The possible reasoning for this could be that due to vitamin A’s antioxidant
properties, the oxidation is kicked into high gear. Though free radicals are thought
to be “bad” they are needed for functions such as killing bacteria and eliminating
new cancer cells. The increase in vitamin A increases the oxidation rates, which
decreases the amount of free radicals available to carry out important tasks. This
illustrates the dangers of taking in too much vitamin A.
So how much is too little or too much? Vitamin A needs are influenced by age,
gender, state of health, and in regards to women, if they are pregnant or not.
Children need less than adults and adult males need more than adult females. The
Recommended Dietary Allowance is 33 mcg/day for children ages 1 – 3 years, 400
mcg/day for ages 4-8 years, and 600 mcg/day for ages 9-13. At the age of fourteen,
gender becomes important. Males over the age of fourteen need 900 mcg/day while
females need 700 mcg/day of vitamin A (6). For women who are pregnant or
breastfeeding, their vitamin A need is even greater than the 700 mcg/day. Women
in the age group of 14-18 who are pregnant need 750 mcg/day and 1,200 mc/day
when breastfeeding. For older women, above the age of 19 years old, the RDA
increases to 770 mcg/day during pregnancy and 1,300 mcg/day while breastfeeding
(10). Women of childbearing age are warned against high doses of vitamin A before
or during pregnancy due to the possible harm that it could bring to the baby.
Women in this group are often warned to stay away from supplements to try and
avoid these mega doses and their effects (11). These numbers should act as goals for
individuals to meet when deciding the foods that will make up their diet. Eating a
variety of foods that act as sources is a good way to help ensure that one’s diet has
enough vitamin A in order to avoid deficiency issues, while not taking in too much
where toxicity could become a factor.
For some individuals, satisfying the RDA is not enough to give them proper
Vitamin A levels. This may be due to the adverse effect medications can have. The
absorption of Vitamin A can be reduced when taking other medications such as
certain weight los treatments. The risk of toxicity may be increased or reached
sooner if an individual is taking certain medications (5). Disease states such as cystic
fibrosis can cause difficulty in obtaining ideal vitamin levels. Cystic fibrosis patients
are commonly deficient due to having a pancreatic insufficiency but can be
improved with pancreatic treatments.
Another concern is the intake of protein. Vitamin A binds to protein and if
there is a lack of protein then vitamin A has nothing to bound to, resulting in a
deficiency of vitamin A. Due to Vitamin A being a fat soluble vitamin, anytime there
is an issue with fat absorption or metabolism, the vitamin level may suffer as well.
Research has also been done to look at the need for dietary zinc and vitamin D
status and the effects on vitamin A, specifically retinoid forms. Given that vitamin A
also has a hand in bone development, its relationship with vitamin D can effect bone
growth. There is evidence to suggest that vitamin D deficiency can be linked with
over supplementation of vitamin A. This helps to remind individuals to control the
aspects of all parts (vitamins, minerals, etc) of their diet can have vast effects on
other nutrients and its ability to serve the body.
Not many other nutrients play as vital of a role in physiological functions as
does Vitamin A. Not only does it allow for eyesight but also it supports immune
function, maintains healthy skin, has a hand in several different cell type synthesis,
and is a possible link in treating various diseases. The importance of this complex
and its compounds have been known for thousands of years and knowledge of the
functions continues to grow. Without adequate amounts of vitamin A, important
biological processes are compromised, most notably that of the immune system and
vision.
References
1) Wolfe, George. "A History of Vitamin A and Retinoids." A History of Vitamin A and
Retinoids. N.p., n.d. Web. 11 Nov. 2013.
<http://www.fasebj.org/content/10/9/1102.long>.
2) Sommer, Alfred. "Journal of Nutrition." Vitamin A Deficiency and Clinical Disease: An
Historical Overview. The Journal of Nutrition, 2008. Web. 11 Nov. 2013.
<http://jn.nutrition.org/content/138/10/1835.full>.
3) "Linus Pauling InstituteMicronutrient Research for Optimum Health." Linus Pauling
Institute at Oregon State University. Linus Pauling Institute, n.d. Web. 11 Nov. 2013.
<http://lpi.oregonstate.edu/infocenter/vitamins/vitaminA/>.
4) "Harvard School of Public Health » The Nutrition Source » Vitamin A." The Nutrition
Source. Harvard School of Public Health, n.d. Web. 11 Nov. 2013.
<http://www.hsph.harvard.edu/nutritionsource/vitamin-a/>.
5) "Vitamin A." — Health Professional Fact Sheet. National Institute of Health, n.d. Web.
11 Nov. 2013. <http://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/>.
6) Medline Plus. "Vitamin A: MedlinePlus Medical Encyclopedia." U.S National Library of
Medicine. U.S. National Library of Medicine, n.d. Web. 11 Nov. 2013.
<http://www.nlm.nih.gov/medlineplus/ency/article/002400.htm>.
7) "Vitamin A." The World's Healthiest Foods. George Mateljan Foundation, 2013.
Web.
<http://www.whfoods.com/genpage.php?tname=nutrient&dbid=106#function
>.
8) "Vitamin A." The World's Healthiest Foods. George Mateljan Foundation, 2013.
Web.
<http://www.whfoods.com/genpage.php?tname=nutrient&dbid=106#function
>.
9) Offit, Paul A. "Don't Take Your Vitamins." New York Times, 8 June 2013. Web.
<http://www.nytimes.com/2013/06/09/opinion/sunday/dont-take-yourvitamins.html?pagewanted=all&_r=0>.
10) "Vitamin A (Retinol)." University of Maryland Medical Center. N.p., 2011. Web.
<http://umm.edu/health/medical/altmed/supplement/vitamin-a-retinol>.
11) Liss, Alan R. "Teratology Society Publications." Teratology Society Publications.
N.p., 2003. Web. <http://teratology.org/pubs/vitamina.htm>.