Vitamin A can be found in several different forms, and food like carrots contain a wealth of vitamin A.
It is a powerful antioxidant and acts as a hormone in the body, affecting the expression of genes and thereby influencing phenotype.
It also helps the heart, lungs, kidneys, and other organs to function correctly.
Contents of this article:
- Vitamin A is vital for growth and development, cell recognition, vision, immune function, and reproduction and helps the heart, lungs, and kidneys.
- Pregnant women and those in developing countries are most at risk of vitamin A deficiency.
- Too much vitamin A can be toxic and cause hypervitaminosis.
- Vitamin A can be found in orange plant foods, meat, eggs, and milk.
Forms of vitamin A
Vitamin A is found in different forms.
Preformed vitamin A occurs in meat, fish, and dairy produce.
Provitamin A is stored in fruits, vegetables, and other plant-based products.
Retinol is the predominant, active form of vitamin A found in the blood. Retinyl palmitate is the storage form of the vitamin.
Beta-carotene is a precursor of vitamin A and is found in plants.
This "pro-vitamin," in itself an antioxidant, is converted into vitamin A as needed by the body, so there is no risk of overdose or toxicity.
As vitamin A affects a wide range of body functions, a deficiency can lead to a variety of problems.
- night blindness
- a higher risk of infections, especially in the throat, chest, and abdomen
- follicular hyperkeratosis, leading to dry, bumpy skin.
- fertility issues
- delayed growth in children
An adequate amount of vitamin A may have the following benefits.
Lowering cancer risk
Treating type 2 diabetes
Healthful skin and hair
Vitamin A is important in the growth of all bodily tissues, including skin and hair.
It contributes to the production of sebum, the oil that helps maintain levels of moisture in the skin and hair.
Leafy greens are a rich source of Vitamin A
Ready-made retinol, the active form of vitamin A, only comes from animal sources.
The richest sources of retinol are:
- organ meats, such as liver
- fatty fish, such herring and salmon, and fish oils
- butter, milk, and cheese
Plant-based foods contain carotenoids, antioxidant forms of vitamin A. These are converted to retinol in the body.
Carotenoid is an orange pigment that contributes to the color of certain fruits and vegetables.
Vegetable sources that are rich in carotenoids are:
- pumpkin , carrots, squash and other orange-colored vegetables
- sweet potatoes
- orange-colored fruits, such as cantaloupes, papayas, and mangos
Plant foods rich in beta-carotene include:
- broccoli, spinach, turnip greens, and other dark, leafy green vegetables
The recommended intake of vitamin A varies according to age and sex.
It is available in several forms, and the vitamin A content in foods is often measured as retinol activity equivalents (RAEs).
One RAE is equal to 1 microgram (mcg) of retinol, 12 mcg of beta-carotene, or 3.33 International Unit (IU) of vitamin A.
The recommended intakes of vitamin A are as follows:
Up to 6 months, the adequate intake (AI) is 400 micrograms (mcg) per day, and from 7 to 12 months, it is 500 mcg per day.
These figures represent the mean intake of vitamin A in healthy, breastfed infants.
- From 1 to 3 years, the requirement is 300 mcg per day
- From 4 to 8 years, it is 400 mcg per day
- From 9 to 13 years, it is 600 mcg per day
- From 14 years, the requirement for males is 900 mcg per day, and for females, 700 mcg per day
- For women aged 19 to 50 years, the requirement is 770 mcg per day during pregnancy and 1,300 mcg per day while breastfeeding
The 2007 to 2008 National Health and Nutrition Examination Survey (NHANES) found that the average American aged 2 years and above consumes 607 mcg of vitamin A per day.
Who is at risk of deficiency?
Preterm infants are one of the most at-risk groups for vitamin A deficiency.
The highest risk of deficiency is among:
- preterm infants
- infants and children in developing countries
- pregnant and lactating women in developing countries
- people with cystic fibrosis
The weight-loss drug Orlistat, also known as Alli and Xenical, reduce the body's ability to absorb fat-soluble vitamins such as vitamin A, increasing the risk of deficiency.
Vitamin A supplements are available for those who have difficulty absorbing the nutrient, but it is best to meet needs through food, not in isolation.
The use of supplements can mask possible deficiencies of other nutrients, potentially leading to acute and long-term health issues.
Potential health risks
Preformed vitamin A can be toxic when consumed in excessive amounts, either through diet or supplementation.
The tolerable upper intake level (UL) for vitamin A varies by age. The UL is the amount above which vitamin A intake may be toxic.
The NIH has established the following ULs:
- up to 3 years: 600 mcg per day
- 4 to 8 years: 900 mcg per day
- 9 to 13 years: 1,700 mcg per day
- 14 to 18 years: 2,800 mcg per day
- 19 years and over: 3,000 mcg per day
Overconsumption of vitamin A can be toxic.
It can lead to:
- skin changes, such as yellowing, cracking, itching, and heightened sensitivity to sunlight
- vision changes and, in younger children, double vision
- brittle nails
- hair changes, like hair loss and oily hair
- weak bones, bone pain, or swelling
- vomiting, dizziness, headaches, and nausea
- difficulty gaining weight and decreased appetite
- gum disease
- fatigue, drowsiness, and changes in alertness
- a bulging fontanelle, or the soft spot in the skull, in children
- liver disease, in cases of extremely excessive intake
Pregnant women should not consume more than the recommended levels of Vitamin A because retinol has been linked with fetal deformities.
Retinol is also available as an anti-aging skin cream. This, too, should not be used by pregnant women.
Beta-carotene and other carotenoids are not as toxic as retinol, as these are only converted into vitamin A when it is needed. The highest risk is with supplements.
Those who take isotretinoin, or Roaccutane, for acne treatment should take care not to consume too much vitamin A, and to avoid vitamin A supplements, because this drug is a vitamin A derivative.
A healthful, balanced diet should provide enough vitamin A without needing supplements.