Vitamin A is an important vitamin required for growth and development, the recognition of cells, vision, immune function and reproduction.
This is a powerful antioxidant and acts as a hormone in the body which affects gene expression and thus influences phenotype.
This also allows proper functioning of the heart, lungs, kidneys and other organs.
Fast facts about vitamin A
- 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.
Types
Vitamin A is present in various ways.
Preformed vitamin A occurs in the processing of meat, fish and milk.
Provitamin A is found in nuts, vegetables, and other items made from plants.
Retinol is the active, primary source of vitamin A present in the blood. Retinyl palmitate is the source of the vitamin which is processed.
Beta-carotene is a vitamin A precursor, which is found in plants.
The “pro-vitamin,” an antioxidant in itself, is converted as required by the body into vitamin A and there is no chance of overdose or toxicity.
Benefits
Since vitamin A affects a wide range of body functions, a deficiency can cause a number of issues.
These include:
- 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
The following benefits may be provided by an sufficient amount of vitamin A.
Lowering cancer risk
Adequate intakes of fruit and vegetable carotenoids are associated with a lower risk of lung cancer but the use of beta-carotene and vitamin supplements did not produce the same results.
One meta-analysis indicates that certain types of vitamin A can help to prevent prostate cancer.
Japanese studies have indicated beta-carotene may help to prevent colon cancer.
Treating type 2 diabetes
Retinoic acid, a vitamin A derivative, was used to normalize blood sugar in diabetic mice.
Healthful skin and hair
Vitamin A is essential for the growth of all tissues in the body, including skin and hair.
It contributes to sebum growth, the oil that helps hold moisture levels in the skin and hair.
Sources
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
- eggs
Plant based foods contain carotenoids, vitamin A antioxidant type. They are converted into body retinol.
Carotenoid is an orange pigment that contributes to the color of certain vegetables and fruits.
Vegetable Carotenoid-rich sources 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
- zucchini
- peppers
Recommended intake
The minimum vitamin A intake varies by age and sex.
It is present in different ways, and the amount of vitamin A in foods is also measured as equal to retinol activity (RAE).
One RAE is equal to 1 microgram (mcg) of retinol, 12 mcg of beta-carotene, or 3.33 International vitamin A unit (IU).
The recommended intake of vitamin A is as follows:
Adequate intake (AI) is 400 micrograms (mcg) per day for up to 6 months, and 500 mcg per day for 7-12 months.
This statistics reflect the mean vitamin A intake of stable, breastfed children.
- 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 National Health and Nutrition Examination Survey (NHANES) from 2007 to 2008 found that the average American age 2 years and over absorbs 607 mcg of vitamin A per day.
Who is at risk of 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, decreases the ability of the body to consume fat-soluble vitamins like vitamin A, which raises the risk of deficiency.
For those that have trouble absorbing the nutrient, vitamin A supplements are available, but it is best to fulfill needs through food, not isolation.
The use of supplements can obscure possible other nutrient shortages, potentially leading to acute and long-term health problems.
Risks
Preformed vitamin A can be harmful if ingested in large amounts, either by diet or by supplement.
The level of tolerable upper intake (UL) for vitamin A varies according to age. The UL is the amount of vitamin A intake above that can be harmful.
The following ULs were developed at the NIH:
- 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
- irritability
- 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 eat more than permissible vitamin A levels because retinol has been related to fetal deformities.
Retinol also comes as a cream for anti-aging skin. Pregnant women do not use this, too.
Beta-carotene and other carotenoids are not as toxic as retinol, as these are converted into vitamin A only when required. With supplements the highest risk is.
Anyone who take isotretinoin or roaccutane for the treatment of acne should be careful not to drink too much vitamin A, and avoid vitamin A supplements as this medication is a derivative of vitamin A.
A safe, balanced diet would include ample vitamin A with no supplements needed.
