Vitamin A

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Vitamin A isn’t a single vitamin, rather it's a group of fat-soluble chemical compounds with similar structures. Vitamin A plays a role in skin, bone and eye health. Getting adequate vitamin A is also critical for supporting immune function.

Both animal and plant-based foods contain vitamin A. However, the forms of vitamin A found in plants, carotenoids, need to be converted to the bioactive form retinol before the human body can use them.

Deficiency of vitamin A is relatively uncommon in developed countries. It’s more common in pregnant women and children in developing countries.

Preformed and Provitamin A

The vitamin A found in animal products is called preformed vitamin A because the human body can use it in its current form. Forms of provitamin A include retinol, retinal and retinoic acid. Retinol is the form of vitamin A found in most dietary sources including salmon, dairy products or liver.

Carotenoids give plants their red, yellow or orange coloring. Some of the most common carotenoids include beta-carotene, alpha-carotene, lutein and lycopene. The most common form in the human diet is beta-carotene, which gives carrots and sweet potatoes their orange flesh.

Carotenoids can be converted to retinol and stored in the liver. The body can also use provitamin A carotenoids as an antioxidant to reduce oxidative stress from metabolism.

The amount of vitamin A listed on nutrition labels is usually listed in IU. Scientists often use RAE (retinol activity equivalents) to standardize the bioavailability of vitamin A from animal and plant sources.

The following conversions from the U.S. Department of Health and Human Service show how 1IU of various vitamin A sources convert to RAE

  • 1IU of retinol = 0.3μg RAE
  • 1 IU of beta-carotene from supplement = 0.15μg RAE
  • 1 IU of beta-carotene from food = 0.05μg RAE
  • 1 IU of alpha-carotene or beta-cryptoxanthin = 0.025 mcg RAE

The liver stores vitamin A until it's needed by the body. Unlike water-soluble vitamins, like the B vitamins and vitamin C, too much vitamin A can cause toxicity. Overdose is most common when vitamin A is supplemented in mega-dosages.

Benefits of Vitamin A

Vitamin A has various benefits related to the eyes, skin and immune system. Because carotenoids can act as an antioxidant, supplementation may lower cancer risk.

Vitamin A promotes eye health

The most well-known benefit of vitamin A is its ability to protect the eyes. Beta-carotene may reduce symptoms of age-related macular degeneration, which is a common cause of blindness in old age. One Italian study1 found patients treated with lutein and zeaxanthin had their symptoms stabilize compared to non-treated patients.

Vitamin A supports immunity

Vitamin A prevents infections from developing. When the body is deficient in vitamin A, immune cells are severely weakened. It’s thought that vitamin A supports the regeneration of mucus2, which lowers the chances of viruses making it into the body.

Vitamin A Prevents Cancer

A diet including foods high in vitamin A can have anti-carcinogenic benefits. In vitro studies3 show that vitamin A can block the growth of skin, bladder, prostate and lung cancer.

One study3 found that supplemental vitamin A reduced the risk of melanoma. However, results are still controversial.

Vitamin A acts as an antioxidant

Besides being a precursor to retinol, beta-carotene also acts as an antioxidant to reduce oxidative stress caused by cellular metabolism. This antioxidant property reduces inflammation throughout the body. Reducing inflammation4 can lower the risk of developing cancer and cardiovascular disease.

Vitamin A preserves skin health

Vitamin A can have benefits for a wide range of skin disorders including psoriasis, eczema and acne5. Vitamin A’s benefits for skin health are due to its anti-inflammatory properties.

Weight loss

Vitamin A doesn’t directly affect metabolism, but many of its other effects indirectly lead to weight loss. Supporting immunity can reduce the frequency of sickness. Vitamin A’s anti-inflammatory benefits may reduce joint pain and make exercising less painful.

Bone Health

Vitamin A intake above and below the RDA can cause issues with bone health. One study6 examined the effect of retinol on the bone health of women with osteoporosis. The study found that retinol had a bone-sparing effect. Plasma levels of all carotenoids except for lutein were lower in women with osteoporosis than in woman without osteoporosis.

How to Use Vitamin A Supplements

A diet high in organ meats, dairy products and fish may provide enough retinol without supplementation. However, people who don’t eat many leafy greens or animal products can take retinol as an oral supplement.

Retinol is also a common ingredient in multivitamins. Some supplements may also include alpha or beta-carotene.

Vitamin A can also be used topically for skin conditions such as eczema or ance. It’s often added to cosmetic products like sunscreen and moisturizers.

Daily Recommended Allowance

According to the Institute of Medicine Panel of Micronutrients, the Recommended daily dosage of vitamin A for an adult man (or boy over 14 years) is 900μg RAE.

  • Adult man (or boy over 14 years) is 900μg RAE.
  • Adult women and girls over 14 should get 700μg RAE per day. Women who are pregnant need more vitamin A. The RDA is set at 770μg RAE per day.
  • Children between the ages of 9-13 need 600μg RAE per day. Children from 1-3 need 300μg RAE per day and children 4-8 need 400μg RAE per day.

All the RDAs use RAE so if vitamin A intake comes primarily from carotenoids, a higher amount of total vitamin A needs to be consumed.

There is no RDA set for beta-carotene, the form of vitamin A found in sweet potato and carrots. There’s also no upper limit set for beta-carotene, but mega-dosages may negatively affect health.

Epidemiological evidence7 shows that taking large amounts of beta-carotene from supplements increases the risk of developing lung cancer and heart disease in smokers.

Symptoms of Vitamin A Deficiency

All of the symptoms of vitamin A deficiency may have other causes. However, anybody experiencing multiple of the following symptoms should have their vitamin A levels checked.

Dry skin and eyes

There are many causes of dry skin that have nothing to do with vitamin A status. However, vitamin A is needed for fibroblasts to create new skin cells.

Vitamin A also protects the skin from UV damage by acting as an antioxidant. Vitamin A deficiency can cause eczema and acne, which is why many skin creams contain vitamin A.

Abnormal dryness of the eyes is another common symptom of vitamin A deficiency. One case study8 of an 88-year-old in Australian woman found that she developed itchy eyes from a vitamin A deficiency. Because of dietary restrictions, her diet consisted exclusively of rice porridge, canned tuna and vitamin B supplements.

Nyctalopia (Night Blindness)

Vitamin A deficiency is a common cause of blindness in developing countries. According to the World Health Organization, over 13.8 children in developing countries have vision problems caused by vitamin A deficiency.

In particular, vitamin A deficiency can cause problems with night vision. Vitamin A deficiency inhibits the pigment found in the retina used for seeing in low light. The pigment is composed primarily of retinal. The body cannot create retinal in large amounts so it must be consumed through food or supplements.

Infertility

Vitamin A deficiency can lead to infertility in both men and women. Vitamin A deficiency can also lead to a higher risk of miscarriage in women9.

Stunted growth

Children who don’t receive adequate vitamin A may have stunted growth or delayed growth. Research shows that supplementing children in developing countries with vitamin A can help restore their growth10.

A study11 in Indonesia found that children who took vitamin A grew 0.15 inches more than children taking a placebo.

Poor wound healing

Poor vitamin A status can slow the healing of wounds12 and injuries.

Vitamin A promotes the production of collagen, which is the most common protein in the body. Research in humans12 shows that elderly men treated with vitamin A had a 50 percent reduction in the size of wounds after taking a vitamin A cream compared to men who did not use the cream.

Vitamin A Toxicity

Vitamin A is fat-soluble. Fat-soluble vitamins accumulate in the liver and when levels of the vitamin are too high there can be health complications. Vitamin A overdose is known as hypervitaminosis A. The upper limit of vitamin A is 3000μg RAE for adults.

Vitamin A toxicity is unique to retinol. Beta-carotene and other provitamin A supplements seem to be safe in mega-dosages of 20-30mg/day. Taking too high of a daily dose of a retinol supplement is the most common cause of vitamin A toxicity.

However, early arctic explorers13 overdosed from vitamin A found in polar bear liver. The livers of moose and seals also contain a dangerous amount of retinol.

Excess intake of vitamin A can lead to side effects such as dizziness, headaches, nausea, skin irritation, joint pain, coma and potential death in extreme cases.

Diets high in beta-carotene can cause carotenoderma, which is a condition where the skin turns orange. Carotenoderma is harmless and is reversed when beta-carotene intake is lowered.

Overdosing on vitamin A can be especially dangerous for pregnant women. Excess vitamin A intake over the upper limit is linked to birth defects.

Who is at Risk of Vitamin A Deficiency

Vitamin A deficiency is relatively rare in developed countries due to the easy access to foods high in vitamin A. The following groups of people are most at risk of vitamin A deficiency.

Premature babies

Vitamin A deficiency is rare in babies in developed countries. However, babies born prematurely may not have an adequate amount of vitamin stored in their livers at birth. The concentration of retinol14 that premature babies store may remain low throughout the first year of their lives.

Babies with vitamin A deficiency14 are at risk of developing diseases that affect their eyes, lungs and GI tract.

Pregnant and lactating women in developing countries

Pregnant women need more vitamin A than most people because they have to store enough vitamin A for themselves and their infant(s).

The World Health Organization estimates 9.8 million pregnant women have xerophthalmia (abnormal dryness of the cornea) from vitamin A deficiency. Pregnant women with vitamin A deficiency are also at a higher risk of infant mortality, abnormal infant growth and anemia.

Babies and children in developing countries

Women with adequate vitamin A stores produce breast milk with enough vitamin A for their children. However, in developing countries, the concentration of vitamin A in breast milk may not be high enough to support children15.

Children may be particularly at risk when they’ve recently stopped breastfeeding if they aren’t getting adequate vitamin A in their diets.

People with cystic fibrosis

People with cystic fibrosis are at risk of vitamin A deficiency16 because they have trouble absorbing fat.

Cross-sectional research17 shows that up to 40 percent of people with cystic fibrosis have vitamin A deficiency.

Foods that Contain Vitamin A

The best sources of carotenoids are fruits and vegetables with bright orange or red flesh. Dark, leafy greens also contain a considerable number of carotenoids. Organ meats, dairy products and fish are the best sources of retinol.

Some people have trouble converting carotenoids into retinol. These people may benefit from increasing their vitamin A intake.

Here is a list of foods with more than 10 percent of the daily value of vitamin A intake per 100g.

Animal Sources

  • Cod Liver Oil 3333 percent DV
  • Cow Liver 1049 percent DV
  • Lamb Liver 832 percent DV
  • Bluefin Tuna 84 percent DV
  • Butter 76 percent DV
  • Goat Cheese 45 percent DV
  • King Mackerel 28 percent DV
  • Cheddar Cheese 27 percent DV
  • Salmon 17 percent DV
  • Eggs 17 percent DV

Plant Sources

  • Sweet Potato 116 percent DV
  • Carrot 95 percent DV
  • Winter Squash 62 percent DV
  • Cantaloupe 19 percent DV
  • Red Pepper17 percent DV
  • Apricot 11 percent DV

 

Citations and Sources

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Simşek M, Naziroğlu M, Simşek H, Cay M, Aksakal M, Kumru S. Blood plasma levels of lipoperoxides, glutathione peroxidase, beta carotene, vitamin A and E in women with habitual abortion. Cell Biochem Funct. 1998;16(4):227-231. [PubMed]
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Ramakrishnan U, Aburto N, McCabe G, Martorell R. Multimicronutrient interventions but not vitamin a or iron interventions alone improve child growth: results of 3 meta-analyses. J Nutr. 2004;134(10):2592-2602. [PubMed]
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Hadi H, Stoltzfus R, Dibley M, et al. Vitamin A supplementation selectively improves the linear growth of indonesian preschool children: results from a randomized controlled trial. Am J Clin Nutr. 2000;71(2):507-513. [PubMed]
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Hunt T. Vitamin A and wound healing. J Am Acad Dermatol. 1986;15(4 Pt 2):817-821. [PubMed]
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Rodahl K, Moore T. The vitamin A content and toxicity of bear and seal liver. Biochem J. 1943;37(2):166-168. [PubMed]
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Oliveira-Menegozzo J, Bergamaschi D, Middleton P, East C. Vitamin A supplementation for postpartum women. Cochrane Database Syst Rev. 2010;(10):CD005944. [PubMed]
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Graham-Maar R, Schall J, Stettler N, Zemel B, Stallings V. Elevated vitamin A intake and serum retinol in preadolescent children with cystic fibrosis. Am J Clin Nutr. 2006;84(1):174-182. [PubMed]
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