April 9, 2016

Are You Getting These Nutrients? - Part 13

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:
  • 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.

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