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Vitamin
A: Crucial for Vision, Necessary for Health
by
Dale Bennett
Vitamin
A is absolutely necessary for health - in fact, I'll go further:
it's absolutely necessary for human life. Without sufficient
Vitamin A, you could suffer poor night vision and in severe cases
total blindness; an impaired immune system and increased
susceptibility to infections, especially ear infections and urinary
tract infections; and deterioration of bones and tooth enamel,
possibly leading to loss of your teeth.
Pregnant
and breastfeeding women should take special care to get the right
amount of this crucial nutrient, as insufficient Vitamin A can
prevent proper fetal and infant development. (In fact, alcohol
consumption during pregnancy is thought to harm unborn children
specifically by preventing the proper metabolism of Vitamin A,
leading to Fetal Alcohol Syndrome.) But consuming too much Vitamin A
when you're pregnant can lead to birth defects. So read on: I'll
be discussing just how much of this nutrient is needed below.
Vitamin
A comes in several forms, in two basic categories: among the types of
Vitamin A that come from plants, beta-carotene is the most common and
well known; types of Vitamin A from animal sources are called
retinoids.
"Retinoids"
- the word sounds a lot like the word "retina," doesn't it?
For good reason: Vitamin A is absolutely necessary for proper
functioning of your retinas, the "screens" at the back of your
eyes where your lenses focus the light from whatever you may be
looking at. In the retina, chemical reactions to the focused light
form nerve impulses that are then transmitted to the brain, allowing
you to see. In the eye, Vitamin A combines with the protein opsin to
form light-absorbing molecules. When you aren't getting enough
Vitamin A, your first symptom will be night blindness, although
daytime vision will at first seem unaffected. If the deficiency
continues for a prolonged period, total blindness may result.
Vitamin
A also plays a crucial chemical role in gene transcription, the
process by which DNA is replicated during the formation of new cells.
We have billions of cells in our bodies, and many of them die every
day and must be replaced by new cells. Each cell in your body carries
your entire genetic code (with the single exception of your sex cells
- sperm or eggs - which carry exactly half). New cells can only
come into being through cell division, and the DNA code from each
cell must be replicated every time. Without sufficient Vitamin A,
this necessary process falters or fails. This can prevent proper
fetal development, as I pointed out earlier, but it can also stunt
the growth of children at any age, and impair our health as adults,
too.
Vitamin
A is also necessary for skin health, as it is a vital nutrient needed
for the proper development of skin cells. Topical preparations of
Vitamin A in the form of retinoids (and some high-dose oral
medications based on this nutrient) have powerful anti-acne
properties, too.
Vitamin
A is also an effective antioxidant - meaning it fights the free
radicals that cause cell damage and constitute one of the main
factors in aging - and contributes to bone and tooth health.
Vitamin A also helps the body's immune system fight off disease.
It's even used in some anti-HIV drugs.
Around
the world, it's estimated that almost one third of infants,
toddlers, and children under six years old have Vitamin A deficiency
- causing over a quarter million of them to go blind every year. A
study in Africa also showed a major reduction in deaths from malaria
when children were given Vitamin A supplementation.
Encouraging
mothers to breastfeed their infants (assuming the mother has
sufficient supply of the nutrient, of course) can help stave off
Vitamin A deficiency in babies. You can get sufficient Vitamin A as a
part of a healthy, natural diet - in fact, that's the best way
you can do it, since there's a synergistic effect - where the
whole is greater than its component parts - when we consume many
nutrients and vitamins and trace elements together in the foods we
evolved to eat. Some foods rich in Vitamin A include spinach, liver,
dandelion greens, sweet potatoes, carrots, broccoli leaves, butter,
and kale. Most of the time, the stronger the color of the fruit or
vegetable, the more beta-carotene it contains.
If
you decide you need Vitamin A supplementation, it's important not
to take too much. For an average adult 900 micrograms (3,000 IU) per
day is about right.
Vitamin
A poisoning can happen if you consume very large quantities of of
vitamin A for many months - authorities say this would take a
prolonged exposure to over 4,200 micrograms (14,000 IU) a day. (There
are some exceptions to the 900 microgram rule of thumb: Ultra-high
Vitamin A doses - for very limited periods - are sometimes
prescribed for those with HIV or severe Vitamin A deficiency.) One
sign of too much beta-carotene consumption is a yellowish
discoloration of the skin, especially on the soles of your feet and
the palms of your hands. It's very unlikely you could ever get this
amount - of any variety of Vitamin A - from foods. It's a
supplementation issue. Supplements are useful in certain situations:
for example, when people are temporarily on a very restricted diet.
But one has to be careful. Some people believe that if one pill is
good, ten pills must be even better. But when it comes to nutrients,
that simply isn't true. Our bodies depend on multiple, complex
chemical processes, and having the right nutrients in the right
proportions is very important. Educate yourself. Make informed
decisions. And take charge of your health and your life!
REFERENCES
Fennema,
Owen; Fennema's
Food Chemistry, CRC
Press, Taylor & Francis, pp. 454-455
Tanumihardjo,
S.A., ."Vitamin A: Biomarkers of nutrition for development,"
American
Journal of Clinical Nutrition
94
Black,
R.E. et al.; Maternal and Child Undernutrition Study Group (2008);
"Maternal and child undernutrition: global and regional
exposures and health consequences". Lancet 371
George
Mateljan Foundation, The
World's Healthiest Foods,
"Vitamin A,"
http://www.whfoods.com/genpage.php?tname=nutrient&dbid=106 ,
accessed April 20, 2014
Mayo
Clinic Online, "Vitamin A,"
http://www.mayoclinic.org/drugs-supplements/vitamin-a/dosing/hrb-20060201
, accessed April 19, 2014
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