This vitamin plays an essential role in the vision, particularly night vision, normal bone growth, reproduction, and the health of skin and mucous membranes (the mucus-secreting layer that lines body regions such as the respiratory tract). Vitamin A also acts in the body as an antioxidant, a protective chemical that may reduce the risk of certain cancers.
There are two sources of dietary vitamin A. Active forms, which are immediately available tot he body, are obtained from animal products. These are know as retinoids and include retinal and retinol. Precursors, also known as pro-vitamins, which must be converted to active forms by the body, are obtained from fruits and vegetables that contain yellow, orange and dark green pigments or carotenoids. The best know is beta-carotene. Vitamin A is measured in micro-grams (mcg) as well as in Retinol Equivalents (RE) 1.0 mcg RE is equivalent to 1.0 mcg of retinol or 6.0 mcg of beta-carotene.
In the intestine, vitamin A is protected from being chemically changed by vitamin E. Vitamin A is fat-soluble and can be stored in the body. Most of the vitamin A you eat is stored in the liver. When required by a particular part of the body, the liver releases some vitamin A, which is carried by the blood and delivered to the target cells and tissues.
Vitamin A deficiency
In many developing countries, a dietary deficiency of vitamin A is common, with pregnant women and infants being the most often affected. In the West, a deficiency is rare, but may occur in people who abuse alcohol or those with long-term conditions that affect their ability to absorb fats, such as cystic fibrosis or Crohn's disease. This is because vitamin A is absorbed in fats. A common symptom of a severe deficiency of vitamin A is the eye disorder xerophthalmia, in which the cornea (the transparent membrane at the front of the eye) hardens. This may progress to night blindness, corneal ulceration, and irreversible blindness.
Other signs and symptoms include growth problems in children, poor wound healing, and dry, bumpy skin rashes know as follicular hyperkeratosis. Vitamin A deficiency can also affect the health of the epidermis (skin) and the normal functioning of mucous membranes throughout the body.
Men 1,000 RE or 5,000 IU
Women 800 RE or 4,000 IU
Vitamin A is found naturally in all these foods, which contain at least 0.15 mcg of the vitamin, or 150 mcg RE, per 50-200g (2-7oz)
- sweet potatoes
- butternut squash
- liver (beef, pork, chicken, or turkey)
- 5,000 international units (IU) daily, preferably as beta-carotene
- Natural sources such as carrots, sweet potatoes, and mangoes
Interactions & Side Effects
- Vitamin A can increase the toxicity of medications that contain Isoretinoin, such as the acne treatment Accutane If you don't get enough vitamin A, you are more susceptible to infectious diseases and vision problems. If you get too much vitamin A, you can become sick. Large doses of vitamin A can also cause birth defects. Acute vitamin A poisoning usually occurs when an adult takes several hundred thousand IU. Symptoms of chronic vitamin A poisoning may occur in adults who regularly take more than 25,000 IU a day. Babies and children are more sensitive and can become sick after taking smaller doses of vitamin A or vitamin A-containing products such as retinol (found in skin creams).
Disclaimer: This website is for information purposes only. By providing the information contained herein we are not diagnosing, treating, curing, mitigating, or preventing any type of disease or medical condition. Before beginning any type of natural, integrative or conventional treatment regime, it is advisible to seek the advice of a licensed healthcare professional.