Vitamin A - retinol

Vitamin A is an important fat soluble vitamin. Carotenoids such as beta-carotene can be converted to vitamin A in the body. Beta-carotene is an antioxidant. Antioxidants can protect cells from damage caused by substances called free radicals.

Vitamin A is important for rhodopsin or visual purple in the retina of the eye, immune response to combat infections and reduce inflammation, integrity of the skin and mucous membranes, key processes in the bones, cell growth and development (pregnancy and childhood), sperm production and quality, and the reproductive cycle in females. Vitamin A is stored in the liver.

Sources

foods containing vitamin A The richest source of vitamin A is liver including cod liver oil. Other good sources of vitamin A are meat, eggs, milk products and fish oil.

Many dark-green or dark-yellow plants (including sweet potatoes, carrots, spinach, and kale) contain carotenoids, which can be converted to vitamin A in the body.

The more intense the color of the vegetable or fruit, the higher the beta-carotene content. Here is a list of foods having the highest content of vitamin A.

Daily intake

The recommended daily intake for adult males is 900 micrograms (~3000 IU) and for adult females 700 micrograms (~2333 IU) . During pregnancy 70 micrograms (~233 IU) should be added and during lactation 500 micrograms (~1666 IU) should be added. (One microgram of Vitamin A is equal to 1/0.3 IU.)

Deficiency

Too little vitamin A can lead to “night blindness” and even dryness and opacity of the cornea (xeropthalmia) leading to blindness, increased vulnerability to infections, goose bump-like appearance of the skin, weakening of mucous membranes, infertility, and abnormal bone growth leading to malformation of bones.

Excess

Toxicity can occur at levels as low as 15,000 IU per day. (One IU is equal to 0.3 micrograms of Vitamin A.) However, the average daily toxic dose is 120,000 IU. In people with renal failure, 4000 IU can cause damage. Also excessive alcohol intake can increase toxicity. Children can reach toxic levels at 1,500 IU/kg body weight.

Excessive vitamin A consumption can lead to nausea, irritability, reduced appetite, vomiting, blurry vision, headaches, hair loss, muscle pain, abdominal pain, weakness, drowsiness, and altered mental status. Chronic toxicity can cause dry skin, dry mucous membranes, fever, insomnia, fatigue, weight loss, bone fractures, anemia, and diarrhea.

Note that carotene forms like beta-carotene from dietary sources are not toxic although the skin can become yellow.

References: 1 , 2