Vitamin A (retinol)


Vitamin A is a fat-soluble vitamin that comes from two sources: preformed retinoids and provitamin carotenoids. Retinoids, such as retinal and retinoic acid, are found in animal sources such as liver, kidney, eggs, and dairy products. Carotenoids, such as beta-carotene (which has the highest vitamin A activity), are found in plants such as dark or yellow vegetables and carrots.
Natural retinoids are present in all living organisms, either as preformed vitamin A or as carotenoids, and are required for biological processes such as vision and cellular growth. A major biologic function of vitamin A (as the metabolite retinal) is in the visual cycle. Research also suggests that vitamin A may reduce death from measles, prevent some types of cancer, aid in growth and development, and improve immune function.
Recommended dietary allowance (RDA) levels for vitamin A oral intake have been established by the U.S. Institute for Medicine of the National Academy of Sciences to prevent deficiencies in vitamin A. At recommended doses, vitamin A is considered nontoxic. Excess dosing may lead to short or long-term toxicity.
Vitamin A deficiency is rare in developed nations but remains a concern in developing countries, particularly in areas where poor nutrition is common. Prolonged deficiency can lead to xerophthalmia (dry eye) and ultimately to night blindness or total blindness, as well as to skin disorders, infections (such as measles), diarrhea, and lung disorders.

Related Terms

3,7-Dimethyl-9-(2,6,6,trimethyl-1-cyclohexen-1-yl)-2,4,6,8-natetraen-1-ol, 3-dehydroretinol, Accutane®, acitretin, adapalene, alitretinoin, all-trans retinoic acid, Altinac®, Amnesteem®, antixerophthalmic vitamin, Aquasol A®, Avita®, axerophtholum, beta-carotene, beta-carotene oleovitamin A, bexarotene, carotenoids, Differin®, etretinate, isotretinoin, Palmitate-A®, Renova®, Retin-A®, Retin-A Micro®, retinaldehyde (RAL), retinyl acetate, retinyl N-formyl aspartamate, retinyl palmitate, retinoic acid, retinol, Solatene®, Soriatane®, SourceCF®, Targretin®, tazarotene, Tazorac®, Tegison®, topical retinoids, tretinoin, Vesabiod®, Vesanoid®, Vitamax®, vitamin A USP, vitamin A1, vitamina A, vitaminum A.

evidence table

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Acne (Grade: A)
Retinoids that are applied to the skin are considered among the best treatments for acne. Tretinoin (all-
Acute promyelocytic leukemia (cancer of blood and bone marrow, treatment) (Grade: A)
The prescription drug all-
Anemia (decrease in red blood cells) (Grade: A)
Vitamin A deficiency has been shown to impair iron use, as well as impair red blood cell formation, and increase the risk of infection. Vitamin A supplementation has been shown to raise hemoglobin levels and serum iron concentrations, particularly in children and pregnant women. It has also been shown to enhance the efficacy of iron supplementation in patients with vitamin A deficiency and iron deficiency anemia.
Dry eyes (xerophthalmia) (Grade: A)
Prolonged vitamin A deficiency can lead to xerophthalmia (dry eye). It is widely seen in rural, underdeveloped areas, such as India and Southeast Asia. Oral vitamin A is the treatment of choice for xerophthalmia caused by prolonged vitamin A deficiency, and it should be given immediately once the disorder is established. Bitot's spot, or the buildup of keratin debris in the conjunctiva, is a sign of xerophthalmia and may also be treated with vitamin A supplementation.
Eye disorders (retinitis pigmentosa) (Grade: A)
Retinitis pigmentosa is a genetic disorder that affects night vision. Early symptoms include night blindness and loss of vision over time. Based on recent findings, vitamin A in the palmitate form has been recommended in patients with retinitis pigmentosa.
Malaria (supportive agent) (Grade: A)
Limited research suggests that vitamin A may reduce fever, morbidity, and parasite blood levels in patients with malaria (
Measles (supportive agent) (Grade: A)
Vitamin A should be given to children diagnosed with measles in areas where vitamin A deficiency may be present. Measles is a viral disease that can lead to diarrhea, pneumonia (lung infection), and encephalitis (inflammation of the brain). In children with measles, vitamin A has been shown to be beneficial by decreasing the length and impact of the disease. Side effects such as diarrhea, pneumonia, and death have been reduced with the use of vitamin A. Management of measles should be under strict medical supervision.
Mortality reduction (childhood; all-cause) (Grade: A)
Vitamin A is needed for healthy growth and development, and recommended dietary allowances (RDAs) should be assured, particularly in children. Major causes of vitamin A deficiency in children are maternal vitamin A deficiency (thus low levels of vitamin A in breast milk), inadequate vitamin A intake upon weaning, and prevalent illness. Experts have maintained that in developing countries, diet alone is insufficient to maintain adequate vitamin A levels in children. Vitamin A is associated with a reduced risk of mortality (death) in children.
Skin damage caused by the sun (Grade: A)
Some studies suggest that topical tretinoin (all-
Vitamin A deficiency (Grade: A)
Vitamin A deficiency is generally rare in industrialized nations. In developing countries, diet alone may be insufficient to maintain adequate vitamin A levels, especially in children. Vitamin A supplementation can help prevent or treat vitamin A deficiency.
Healing after photorefractive keratectomy (adjunct therapy) (Grade: B)
Photorefractive keratectomy is a type of laser eye surgery used to correct nearsightedness. High-dose vitamin A use in addition to vitamin E has been suggested to help improve eye healing after surgery and to improve visual acuity, although additional evidence is necessary before a definitive conclusion can be reached.
HIV support (Grade: B)
The role of vitamin A in the prevention, transmission, or treatment of HIV is controversial and not well established. A clear conclusion cannot be formed based on the available scientific research.
Oral leukoplakia (white patches or plaque in the mouth) (Grade: B)
Vitamin A may improve clinical resolution of oral leukoplakia (white patches or plaque in the mouth), although relapse is common. Further research is required.
Age-related macular degeneration (Grade: C)
Although this has not been well studied in humans, the use of vitamin A and carotenoids may be useful in the prevention of age-related macular degeneration. Further research is required.
Asthma (Grade: C)
Vitamin A intake is inversely associated with asthma risk and severity. A clear conclusion cannot be formed based on the available scientific research.
Breast feeding (nipple pain) (Grade: C)
Vitamin A and D ointment may be useful for sore and cracked nipples that occur during breastfeeding. However, available studies have not shown vitamin A or any other topical therapy to relieve the pain of breastfeeding.
Bronchiolitis (inflammation of the bronchioles) (Grade: C)
Vitamin A is thought to be important in immune function. A clear conclusion cannot be formed on the effects of vitamin A on bronchiolitis (inflammation of the bronchioles) based on the available scientific research.
Bronchopulmonary dysplasia in premature infants (chronic lung condition) (Grade: C)
Research results are lacking as to whether vitamin A is beneficial for bronchopulmonary dysplasia in premature infants. Further research is needed.
Cancer (general) (Grade: C)
Research has shown mixed results for cancer risk reduction with vitamin A use, and some studies suggest an increased risk of cancer with vitamin A supplementation. According to a review of epidemiological studies, beta-carotene may be most beneficial in prevention of renal cancer, while vitamin A appears to be harmful in heavy smokers at risk for lung cancer. Further research is needed to clarify risk status in various populations.
Cataract (Grade: C)
Antioxidants have been suggested in delaying cataract progression. However, research suggests that beta-carotene lacks the ability to reduce risk. Further trials are required to form conclusions.
Cervical cancer (Grade: C)
Human research suggests that vitamin A may have protective effects in cervical cancer. Compared to low intakes and low serum levels, high intake and high serum levels were associated with a decreased risk of cervical cancer. Further, high quality research is needed.
Chemotherapy adverse effects (Grade: C)
The effect of vitamin A supplementation on chemotherapy-related side effects, including nausea, vomiting, diarrhea, or mouth sores, is unclear. Also, it is unclear if vitamin A interacts with chemotherapy agents. Further research is needed.
Colorectal cancer (Grade: C)
Alpha-carotene and vitamin A may protect against recurrence of colorectal cancer in nonsmokers and nondrinkers. Further research is needed before a conclusion can be drawn.
Cystic fibrosis (Grade: C)
In people with cystic fibrosis, intake and absorption of fat-soluble antioxidants such as carotenoids are reportably lower. However, high-quality human research is lacking, and further research is needed in this field.
Liver cancer (Grade: C)
Some forms of vitamin A may be beneficial in liver cancer prevention. Acyclic retinoid is a synthetic retinoid that has been shown to inhibit cell growth in liver cancer cells. Further research is needed.
Liver disease (Grade: C)
There is insufficient evidence on the use of antioxidant supplements (including vitamin A) in patients with liver disease. More research is needed in this area.
Lung cancer (Grade: C)
Vitamin A has been studied as a possible treatment for lung cancer, without evidence of benefits. The available evidence suggests that high-dose vitamin A and beta-carotene may actually increase the risk of adverse effects, especially among alcohol users and smokers.
Miscarriage (prevention) (Grade: C)
Poor nutrition is associated with an increased risk of miscarriage. However, excess intake of vitamin A has been reported to increase the risks of some birth defects. Vitamin A supplementation above the recommended daily amount is not advised in pregnancy.
Mortality reduction (Grade: C)
Adequate vitamin A (either through diet or supplementation) appears to have a major role in the prevention of morbidity and mortality. Further research is needed.
Mortality reduction (maternal; supplementation after childbirth) (Grade: C)
Maternal supplementation of vitamin A shortly after childbirth provides limited number of benefits to maternal health status. A clear conclusion is lacking based on the available scientific research.
Mortality reduction (maternal; supplementation during pregnancy) (Grade: C)
Vitamin A supplementation during pregnancy and lactation does not appear to reduce infant morbidity and mortality; however, it does appear to reduce maternal morbidity. A clear conclusion cannot be formed based on the available scientific research.
Mouth sores (oral lichen planus) (Grade: C)
Early research suggests a positive effect of retinoid treatment for oral lichen planus; however, more research is required to form conclusions.
Nutrition supplementation (Grade: C)
In developing countries, and in diets of developed countries where limited amounts of vitamin A are consumed, vitamin A intake is of concern. Upon analysis of small fish consumed in developing countries, high levels of vitamin A, iron, and zinc were collected, suggesting an alternative source to increase micronutrient intake. In young children under the age of two, fortified milk and cereals increased levels of vitamin A, and according to some research, micronutrient powders decreased iron deficiency and anemia. Further research is required to make conclusions of vitamin A intake in these populations.
Ovarian cancer (Grade: C)
Research of vitamin A intake suggests a lack of relationship between self-recalled antioxidant consumption from foods and ovarian cancer risk; however, adolescent intake appeared to reduce risk by 46%. Further research is needed to make conclusions based on these findings.
Parasite infection (Ascaris reinfection) (Grade: C)
After deworming, children supplemented with vitamin A may be less prone to the
Prostate cancer prevention (Grade: C)
It is unclear whether dietary vitamin A affects prostate cancer risk. Interventional studies are lacking. More research is needed in this area.
Psoriasis (Grade: C)
The use of vitamin A in psoriasis treatment has been reviewed and discussed. Research has shown that treatment with vitamin A reduces psoriasis symptoms.
Radiation therapy side effects (Grade: C)
In some research, vitamin A supplementation appeared to reduce symptoms of chronic radiation proctopathy (damage from pelvic radiation); however, significance was lacking. Further research is needed to form conclusions.
Rosacea (Grade: C)
Isotretinoin is a well-known treatment for rosacea; however, high quality studies and optimal dosages are lacking. Future research is needed.
Skin cancer (Grade: C)
It is unclear if vitamin A or beta-carotene, taken by mouth or used on the skin with sunscreen, is beneficial in the prevention or treatment of skin cancers or wrinkles.
Throat cancer (esophageal) (Grade: C)
Higher intakes of beta-carotene and vitamin A were associated with reduced risk of esophageal adenocarcinoma. There is insufficient evidence to form a clear conclusion at this time.
Tuberculosis (bacterial lung infection) (Grade: C)
There is insufficient evidence to assess the use of vitamin A for tuberculosis. Further research is needed before a conclusion can be drawn
Viral infection (Norovirus (NoV) infection) (Grade: C)
Vitamin A supplementation has been suggested to help prevent NoV infection in children and to reduce the symptoms associated with NoV infections. More research is needed in this area.
Weight loss (Grade: C)
Daily vitamin A with calcium has been suggested for weight loss. In one study, an average loss of two pounds was reported after two years of supplementation in young women. More research is needed in this area.
Wound healing (Grade: C)
In preliminary research, vitamin A (retinol palmitate) significantly reduced rectal symptoms of radiation proctopathy (damage from pelvic radiation), perhaps because of wound-healing effects. Further research is needed to confirm these results.
Arthritis (Grade: D)
The available evidence lacks support for the treatment of any form of arthritis with vitamin A (or combination products containing vitamin A). Further research is needed to confirm these results.
Breast cancer (Grade: D)
Research has suggested that beta-carotene in combination with other antioxidants may reduce mortality in individuals with breast cancer, but the effects of beta-carotene alone are lacking. A reduction in breast cancer risk was reported with high vitamin A or retinol intake; however, significant concerns still exist. Additional research is needed before a conclusion may be made.
Childhood growth promotion (Grade: D)
Vitamin A is necessary for healthy growth and development, and recommended dietary amounts should be assured, particularly in children. Overall, the available evidence has shown a lack of any significant changes in growth in children with respect to height and weight due to vitamin A.
HIV (mother-to-child transmission) (Grade: D)
Overall evidence lacks the support of vitamin A use in HIV-infected pregnant women to reduce mother-to-child transmission of HIV.
Infant mortality (maternal supplementation after childbirth) (Grade: D)
Overall, studies suggest a lack of effect of vitamin A supplementation shortly after childbirth on infant mortality.
Infant mortality (maternal supplementation during pregnancy) (Grade: D)
Overall, studies suggest a lack of effect of prenatal vitamin A supplementation on perinatal or neonatal infant mortality.
Infant mortality (neonatal or childhood supplementation) (Grade: D)
There is a lack of effect of vitamin A on mortality as reported in some research; however, in developing countries, vitamin A supplementation appeared to be helpful in reducing mortality up to six months of age. Further research is needed in this area.
Inflammatory bowel disease (Grade: D)
Some research has shown that isotretinoin lacks a significant effect on the incidence of inflammatory bowel disease (IBD), Crohn's disease (CD), or ulcerative colitis (UC). Additional high quality research is needed before a conclusion may be made.
Respiratory tract infections (Grade: D)
There is insufficient evidence to support the use of vitamin A for the reduction of pneumonia or mortality in children without measles. More research is needed in this area.
Cancer (gastrointestinal; prevention) (Grade: F)
Evidence suggests that vitamin A fails to reduce the rates of gastric cancer or precancerous gastric lesions and also links vitamin A supplementation with increased mortality.