Vitamin A occurs in different forms. The list below will provide more detail.
- Preformed vitamin A occurs in meat, fish, and dairy produce.
- Provitamin A is present in fruits, vegetables, and other plant-based products.
- Retinol is the main active form of vitamin A in the blood. Retinyl palmitate is the storage form of the vitamin.
- Beta-carotene is a provitamin, or a precursor of vitamin A that occurs in plants especially dark colored fruits and vegetables and oily fruits.
Beta-carotene is, in itself, an antioxidant, but the body can also convert it into vitamin A as needed.
Vitamin A contributes to various bodily functions and helps prevent a range of problems, including:
- night blindness
- infections, especially in the throat, chest, and abdomen
- follicular hyperkeratosis, which can lead to dry, bumpy skin
- fertility issues
- delayed growth in children
Consuming an adequate amount of vitamin A may have the following benefits.
Lower cancer risk
Some experts have looked at whether or not adequate intakes of carotenoids can help reduce the risk of lung, prostate, and other types of cancer. However, research has produced mixed results.
The form of vitamin A will depend on the source. For example, ready-made retinol which is the active form of vitamin A only comes from animal sources. The richest sources of retinol include:
- organ meats, such as liver
- fatty fish, such as tuna and herring
- milk and cheese eggs
Plant-based foods contain carotenoids, which are antioxidant forms of vitamin A. The body converts these into retinol as it needs. Carotenoid is an orange pigment that contributes to the color of certain fruits and vegetables. Fruit and vegetable sources that are rich in carotenoids are often orange. They include:
- sweet potato
- red peppers
Plant foods that are rich in beta-carotene include dark green leafy vegetables, such as:
- turnip greens
The recommended intake of vitamin A varies according to age. People also need more during pregnancy and while breastfeeding. 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 from food
- 2 mcg of beta- carotene from supplements
- 3.33 international units of vitamin A
The recommended daily allowances of vitamin A by age are as follows:
- up to 6 months: 400 mcg
- 712 months: 500 mcg
- 13 years: 300 mcg
- 48 years: 400 mcg
- 913 years: 600 mcg
- 14+ years: 900 mcg for males and 700 mcg for females
During pregnancy, the requirement is 770 mcg per day. While breastfeeding, it is 1,300 mcg per day. The 20072008 National Health and Nutrition Examination Survey found that the average U.S. individual, aged 2 years and above, consumes 607 mcg of vitamin A per day.
Who is at risk of deficiency?
Those at highest risk of deficiency include:
- preterm infants
- infants and children in developing countries
- pregnant and lactating people in developing countries
- people with cystic fibrosis
People who use the weight loss drug orlistat may have a higher risk of deficiency. Orlistat reduces the body's ability to absorb fat soluble vitamins such as vitamin A. Vitamin A supplements are available for those whose bodies have difficulty absorbing the nutrient, but it is best to meet needs through food, where possible. This is because the use of supplements can mask possible deficiencies of other nutrients. This may lead to further health issues.
Preformed vitamin A can be toxic when people consume too much, either through their diet or through supplementation. The tolerable upper intake level for vitamin A varies by age. The upper intake level is the amount above which vitamin A intake may be toxic. The list below details the upper intake levels for preformed vitamin A by age:
- up to 3 years: 600 mcg per day
- 48 years: 900 mcg per day
- 913 years: 1,700 mcg per day
- 1418 years: 2,800 mcg per day
- 19+ years: 3,000 mcg per day
It does not appear that a person can consume too much beta-carotene, as the body will only convert it into vitamin A as necessary.
Vitamin A toxicity
That said, consuming too much preformed vitamin A can lead to vitamin A toxicity, or hypervitaminosis A. Symptoms can include:
- changes in skin color
- peeling on the palms of the hands and soles of the feet
- cracked skin on the fingers
- allergic contact dermatitis
- ectropion, which affects the skins around the eyes
- dry lips, mouth, and nose, which can increase the risk of infection
- reduced sebum production
Long-term overuse can lead to:
- changes in bone formation
- high cholesterol levels
- liver damage
- nervous system changes leading to headaches, nausea, and vomiting
During pregnancy, consuming too much retinol can increase the risk of an infant being born with:
- cleft palate
- heart problems
- hydrocephalus, or water on the brain
- problems with the thymus gland, which produces white blood cells
The use of the topical treatment retinol may also increase vitamin A levels to an unhealthy level. People tend to use retinol as an anti-aging skin cream. Topical products can have adverse effects on the skin, though these will likely be less severe than those resulting from oral overconsumption. However, people should avoid using them during pregnancy.
The highest risk of overconsumption is with supplements. A healthful, balanced diet is unlikely to lead to toxic levels of vitamin A. It should also provide enough vitamin A without needing supplements.
Vitamin A is an essential nutrient that contributes to many functions in the body, such as protecting eye health. In the U.S., deficiency is rare. Most people can meet their needs for vitamin A through their diet. In some cases, however, a doctor may recommend supplements. Anyone who uses vitamin A supplements should take care to follow the doctor's instructions, as some forms of vitamin A can be toxic in high doses.
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