Vitamin A is a fat-soluble vitamin that
has several important functions in the body.
- It helps cells reproduce normally, a process called cellular differentiation.
- It is essential for good vision. The first sign of a vitamin A deficiency is often poor sight at night.
- It is needed for the proper development of an embryo and fetus.
Vitamin A helps keep skin and mucous
membranes that line the nose, sinuses, and mouth healthy. It also
plays a role in - immune system function, growth, bone formation,
reproduction, and wound healing.
Vitamin A comes from two sources. One
group, called retinoids, comes from animal sources and includes
retinol. The other group, called carotenoids, comes from plants and
includes beta-carotene. The body converts beta-carotene to vitamin
A. Major carotenoids, including lycopene, lutein, and zeaxantuin,
have important biological properties, including antioxidant and
photoprotective activities.
It is rare in the developed world to
have a serious deficiency of vitamin A. Symptoms include - dry eyes,
night blindness, diarrhea, and skin problems.
While vitamin A is essential for good
health, it can be toxic in high doses. Never take more than the
recommended daily allowance without first talking to your doctor.
Vitamin A in the form of retinyl
palmitate is found in - beef, calf, and chicken liver, eggs, fish
liver oils, and dairy products, including whole milk, whole milk
yogurt, whole milk cottage cheese, butter, and other cheeses.
The body can also make vitamin A from
beta-carotene and other carotenoids, which are fat-soluble nutrients
found in fruits and vegetables that give them their color. Most
dark-green leafy vegetables and deep yellow/orange vegetables and
fruits, sweet potatoes, carrots, pumpkin and other winter squashes,
cantaloupe, apricots, peaches, and mangoes, contain substantial
amounts of beta-carotene. By eating these beta-carotene-rich foods,
you can increase levels of vitamin A in your body.
Vitamin A supplements are available as
either retinol or retinyl palmitate. Tablets or capsules are
available in a variety of doses. The tolerable upper limit, or safe
upper limit, is 10,000 IU. For any dose close to that amount, a
doctor should help you determine the amount to take. Most
multivitamins contain the recommended dietary allowance (RDA) for
vitamin A.
Unlike vitamin A, beta-carotene does
not build up in the body. However, there is some evidence that high
doses of beta-carotene can carry some risk. Talk to your doctor
before taking more than the recommended amount.
Vitamin A is absorbed along with fat in
the diet. Take it with food.
Studies often use high doses of vitamin
A. However, such high doses can be toxic. A doctor should monitor
any high-dose therapy (any dose approaching the level of 10,000 IU
for an adult, or above the recommended daily allowance for a child).
Daily dietary intakes for vitamin A
are:
Adult
- Men, 19 years and older: 900 mcg
- Women, 19 years and older: 700 mcg
- Pregnant women, 14 to 18 years: 750 mcg
- Pregnant women, 19 years and older: 770 mcg
- Breastfeeding women, 14 to 18 years: 1,200 mcg
- Breastfeeding women, 19 years and older: 1,300 mcg
Because of the potential for side
effects and interactions with medications, you should take dietary
supplements only under the supervision of a knowledgeable doctor.
Taking too much vitamin A when you are
pregnant can cause serious birth defects. Because all prenatal
vitamins contain some vitamin A, you should not take a separate
vitamin A supplement.
Synthetic vitamin A can cause birth
defects. Women who are pregnant or trying to become pregnant
shouldn't take this form of vitamin A.
Too much vitamin A is toxic and can
cause liver failure, even death. Symptoms of vitamin A toxicity
include – headache, fatigue, muscle and joint pain, dry skin and
lips - dry or irritated, nausea or diarrhea, and hair loss.
Vitamin A from foods is considered
safe. However, you can get too much from supplements. For adults,
19 and older, the tolerable upper limit for vitamin A is 10,000 IU
per day. Talk to your doctor before taking any dose close to that
amount.
People who have liver disease or
diabetes should not take vitamin A supplements without their doctor's
supervision.
Smokers and people who drink heavy
amounts of alcohol should not take beta-carotene supplements.
Both vitamin A and beta-carotene may
increase triglycerides, which are fats in the blood. They may even
increase the risk of death from heart disease, particularly in
smokers.
Vitamin A is found in many different
vitamin formulas. Supplements that say "wellness formula,"
"immune system formula," "cold formula," "eye
health formula," "healthy skin formula," or "acne
formula," all tend to contain vitamin A. If you take a variety
of different formulas, you could be at risk for too much vitamin A.
If you take large doses of vitamin A,
you may want to avoid eating carob. It increases the amount of
vitamin A available in your body.
No comments:
Post a Comment