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Get to Know about Vitamin A | Article

Get to Know about Vitamin A

Vitamin A (retinol) and vitamin A beta-carotene.  Vitamin A is a fat soluble vitamin that has antioxidant functions.  Retinoids and carotene (vitamin A; including retinol, retina, retinyl esters, and retinoic acid and also referred to as vitamin A. beta carotene can be easily converted to vitamin A as needed.)

This is provided by the diet in two forms:
  • Already formed vitamin A (which is naturally found only in animal products)
  • Vitamin A carotenoid precursors (found mainly in foods of plant origin).
Beta-carotene is the main precursor of vitamin A which also has anti-oxidant properties.  Vitamin A is an important agent for vision, embryogenesis, reproduction, membrane structure integrity, epithelial differentiation, growth, and development.

Benefit :
  • Important for vision
  • Lycopene can reduce the risk of prostate cancer.
  • Maintain healthy tissue and skin.
  • Play an important role in bone growth and in the immune system.
  • Diets rich in alpha carotene and lycopene carotenoids seem to reduce the risk of lung cancer.
  • Carotenoids act as antioxidants.
  • Foods that are rich in carotenoids lutein and zeaxanthin can protect against cataracts.

Can be found at :
  • Sources of retinoids: beef liver, eggs, shrimp, fish, fortified milk, butter, cheddar cheese, Swiss cheese.
  • Sources of beta carotene: sweet potatoes, carrots, pumpkins, squash, spinach, mangoes, turnip greens.

Side effect

Vitamin A is mostly formed from food and supplements.  Large amounts of vitamin A (but not beta carotene) can be harmful to bones.

Vitamin intake in abundance can have a damaging effect on bones through the induction of osteoporosis.  This can lead to an increased risk of fracture, especially in those who have a previous risk of osteoporosis.

Several studies have shown that high intake of vitamin A can cause an increased risk of hip fracture.  One study showed that there was a 68% risk of hip fracture for every 1 mg increase in daily intake of retinol (95% CI, 18% to 140%; P for trend, 0.006).

In the Iowa women's health study, there was a greater risk of hip fracture in vitamin A users, but there was no clear dose-response.

They prospectively followed 34703 postmenopausal women for almost 9.5 years.  It was shown that the risk of hip fracture was 1.18-fold vitamin A complements users compared to non-users (95% CI, 0.99 to 1.41), but there was no greater risk of all fractures among users of vitamin A supplements.

The importance of vitamin A in the bone renovation process has been shown in various studies.  Vitamin A deficiency results in underdeveloped bone growth, but on the other hand hypervitaminosis is leading to accelerated bone resorption, bone fragility, and spontaneous fractures.

Both osteoblasts and osteoclasts express nuclear receptors for retinoic acid (retinoic acid receptors and x retinoid receptors).  Retinoic acid inhibits osteoblast activity, stimulates osteoclast formation, and induces bone resorption.

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