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Vitamin A

 

Natural Standard Monograph, Copyright © 2014 (www.naturalstandard.com). Commercial distribution prohibited. This monograph is intended for informational purposes only, and should not be interpreted as specific medical advice. You should consult with a qualified health care professional before making decisions about therapies and/or health conditions.

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.

Background

  • 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.

Evidence

 

Uses based on scientific evidence 

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 professional.

Grade* 

Acne 

Retinoids that are applied to the skin are considered among the best treatments for acne. Tretinoin (all-trans retinoic acid) and other forms of vitamin A, retinoids, and oral prescription medications, such as isotretinoin (Accutane®), are available for treatment. Isotretinoin may cause severe side effects, such as burning, erythema, and pruritus, and should be used only for severe resistant acne. Adapalene (Differin®) is also effective and reported to have fewer side effects. Another retinoid, tazarotene (Tazorac®), has been shown to be superior to either tretinoin or adapalene. In general, retinoid use (including tretinoin) must be avoided in women that are pregnant, plan to become pregnant, or have a chance of being pregnant, due to a risk of severe birth defects. These medications should be prescribed by a qualified licensed healthcare professional. Multiple retinoid use should be avoided, due to a risk of increased toxicity.

A 

Acute promyelocytic leukemia (cancer of blood and bone marrow, treatment) 

The prescription drug all-trans retinoic acid (ATRA, Vesanoid®) is a form of vitamin A that is a recognized treatment for acute promyelocytic leukemia that improves survival in this disease. Treatment should be under strict medical supervision. Other vitamin A forms should not be used at the same time with ATRA, due to a risk of increased toxicity.

A 

Anemia (decrease in red blood cells) 

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.

A 

Dry eyes (xerophthalmia) 

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.

A 

Eye disorders (retinitis pigmentosa) 

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.

A 

Malaria (supportive agent) 

Limited research suggests that vitamin A may reduce fever, morbidity, and parasite blood levels in patients with malaria (Plasmodium falciparum infection). However, there is a lack of evidence suggesting that vitamin A is equal to or superior to well-established drug therapies used for the prevention or treatment of malaria. Patients with malaria or those who are living or traveling in diseased areas should speak with a physician about appropriate measures.

A 

Measles (supportive agent) 

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.

A 

Mortality reduction (childhood; all-cause) 

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.

A 

Skin damage caused by the sun 

Some studies suggest that topical tretinoin (all-trans retinoic acid, the acid form of vitamin A) may improve sun damaged skin. Common adverse effects are skin pain and redness.

A 

Vitamin A deficiency 

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.

A 

Healing after photorefractive keratectomy (adjunct therapy) 

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.

B 

HIV support 

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.

B 

Oral leukoplakia (white patches or plaque in the mouth) 

Vitamin A may improve clinical resolution of oral leukoplakia (white patches or plaque in the mouth), although relapse is common. Further research is required.

B 

Age-related macular degeneration 

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.

C 

Asthma 

Vitamin A intake is inversely associated with asthma risk and severity. A clear conclusion cannot be formed based on the available scientific research.

C 

Breast feeding (nipple pain) 

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.

C 

Bronchiolitis (inflammation of the bronchioles) 

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.

C 

Bronchopulmonary dysplasia in premature infants (chronic lung condition) 

Research results are lacking as to whether vitamin A is beneficial for bronchopulmonary dysplasia in premature infants. Further research is needed.

C 

Cancer (general) 

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.

C 

Cataract 

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.

C 

Cervical cancer 

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.

C 

Chemotherapy adverse effects 

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.

C 

Colorectal cancer 

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.

C 

Cystic fibrosis 

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.

C 

Liver cancer 

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.

C 

Liver disease 

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.

C 

Lung cancer 

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.

C 

Miscarriage (prevention) 

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.

C 

Mortality reduction 

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.

C 

Mortality reduction (maternal; supplementation after childbirth) 

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.

C 

Mortality reduction (maternal; supplementation during pregnancy) 

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.

C 

Mouth sores (oral lichen planus) 

Early research suggests a positive effect of retinoid treatment for oral lichen planus; however, more research is required to form conclusions.

C 

Nutrition supplementation 

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.

C 

Ovarian cancer 

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.

C 

Parasite infection (Ascaris reinfection) 

After deworming, children supplemented with vitamin A may be less prone to the Ascaris parasite reinfection. These benefits may be less in children with stunted growth. More research is needed in this area.

C 

Prostate cancer prevention 

It is unclear whether dietary vitamin A affects prostate cancer risk. Interventional studies are lacking. More research is needed in this area.

C 

Psoriasis 

The use of vitamin A in psoriasis treatment has been reviewed and discussed. Research has shown that treatment with vitamin A reduces psoriasis symptoms.

C 

Radiation therapy side effects 

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.

C 

Rosacea 

Isotretinoin is a well-known treatment for rosacea; however, high quality studies and optimal dosages are lacking. Future research is needed.

C 

Skin cancer 

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.

C 

Throat cancer (esophageal) 

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.

C 

Tuberculosis (bacterial lung infection) 

There is insufficient evidence to assess the use of vitamin A for tuberculosis. Further research is needed before a conclusion can be drawn

C 

Viral infection (Norovirus (NoV) infection) 

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.

C 

Weight loss 

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.

C 

Wound healing 

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.

C 

Arthritis 

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.

D 

Breast cancer 

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.

D 

Childhood growth promotion 

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.

D 

HIV (mother-to-child transmission) 

Overall evidence lacks the support of vitamin A use in HIV-infected pregnant women to reduce mother-to-child transmission of HIV.

D 

Infant mortality (maternal supplementation after childbirth) 

Overall, studies suggest a lack of effect of vitamin A supplementation shortly after childbirth on infant mortality.

D 

Infant mortality (maternal supplementation during pregnancy) 

Overall, studies suggest a lack of effect of prenatal vitamin A supplementation on perinatal or neonatal infant mortality.

D 

Infant mortality (neonatal or childhood supplementation) 

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.

D 

Inflammatory bowel disease 

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.

D 

Respiratory tract infections 

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.

D 

Cancer (gastrointestinal; prevention) 

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.

F 

 

*Key to grades: 

A: Strong scientific evidence for this use;
B: Good scientific evidence for this use;
C: Unclear scientific evidence for this use;
D: Fair scientific evidence against this use (it may not work);
F: Strong scientific evidence against this use (it likely does not work).

For full grading rationale, click here.

Uses based on tradition or theory 

The below uses are based on tradition or scientific theories. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified health care professional

Aging, AIDS (adjunct), allergic rhinitis, autism, burns, chemical sensitivities (pollutant protection), chronic diseases (prevention), conjunctivitis, deafness, deficiency (protein), diabetes, diarrhea, dysentery (shigellosis), dysmenorrhea, eczema, epilepsy, fibrocystic breast disease, gastric ulcers, glaucoma, hay fever, headache (persistent), heart disease, herpes (cold sores), hyperthyroidism (increased thyroid function), immune enhancement, increasing sperm count, infections (general, nose), kidney stones, lichen planus pigmentosus, menorrhagia (heavy menstruation), metabolic disorders (Hurler syndrome), mouth cancer, neurodegenerative diseases, pancreatic cancer, pancreatitis, periodontal disease, pityriasis rubra pilaris (skin disorder), premenstrual syndrome (PMS), respiratory disorders, sebaceous cysts, sinus infections, sinusitis, skin disorders (Darier's disease, ichthyosis), sleep (regulation), smell disorders, stroke, sunburn, tinnitus, tumors (neoplasms), ulcers (stress ulcers in severely ill hospitalized patients), urinary tract infection, vaginal atrophy, vaginal infections, vascular diseases (prevention), vision enhancement (nearsightedness, blurred vision), warts.


Safety

The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare professional before starting a new therapy. Consult a healthcare professional immediately if you experience side effects.

Allergies

  • Avoid in individuals with a known sensitivity or allergy to vitamin A or any part of the formulation.

Side Effects and Warnings

  • Vitamin A is considered safe when consumed in recommended dietary allowances (RDAs). Adults who eat fortified foods with vitamin A, such as low-fat dairy products and a lot of fruits and vegetables, generally lack the need for supplements or multivitamins that contain vitamin A.
  • Vitamin A may cause bleeding in the lungs, blurry vision, bone pain, breathing difficulty, changes in immune function, chronic inflammation of the liver, cirrhosis (scarring of liver), cough, cracked fingernails, cracked lips, death, decreased thyroid function, depression, diarrhea, feeling of fullness, fever, fluid around heart, hair loss, high cholesterol, increased pressure in the brain, increased risk of HIV transmission (through breastfeeding), increased risk of lung cancer, increased risk of heart disease, increased white blood cells, indigestion, inflammation of the conjunctiva (conjunctivitis), injection site pain, irritability, joint pain, mouth ulcers, muscle pain, psoriasis flare-ups, pain, perisinusoidal fibrosis (in the liver), redness (from skin use), respiratory infection, seizure, skin irritation, sore eyes, steatosis (fatty change), stomach and intestine adverse effects, and suicidal thoughts.
  • Vitamin A toxicity is rare in the general population. Vitamin A toxicity can occur with high amounts of vitamin A taken over short or long periods of time. Consequently, toxicity can be short or long-term. Symptoms of acute (short-term) toxicity include nausea, headache, fatigue, loss of appetite, dizziness, dry skin, desquamation (loss of skin), and cerebral edema (swelling in the brain). Symptoms of chronic (longer-term) toxicity include dry itchy and cracking skin, desquamation, dry lips, scaling anorexia, headache, psychiatric changes, cerebral edema (excess fluid), bone and joint pain, osteoporosis (bone loss), and hip fracture. Severe toxicity can lead to eye damage, high levels of calcium, and liver damage. In children, signs of toxicity include irritability, drowsiness, dizziness, delirium, coma, vomiting, diarrhea, increased pressure in the brain with bulging fontanelles in infants, headache, swelling of the optic (eye) disk, bulging eyeballs, visual disturbances, and skin redness and peeling.
  • People with liver disease and high alcohol intake may be at risk for liver toxicity from vitamin A supplementation. Vitamin A toxicity may lead to intrahepatic cholestasis, where bile cannot flow from the liver into the intestines.
  • Vitamin A may cause low blood pressure. Caution is advised in people with low blood pressure or in those taking drugs or herbs and supplements that lower blood pressure.
  • Use cautiously in combination with bile acid sequestrants, mineral oil, neomycin, or orlistat, due to reduced absorption of vitamin A.
  • Use cautiously in combination with contraceptives taken by mouth, due to increased levels of vitamin A.
  • Use cautiously in combination with alcohol or anticancer agents, due to the potential for increased risk of adverse effects.
  • Smokers who consume alcohol and beta-carotene may be at an increased risk for lung cancer or heart disease. Use cautiously in smokers who consume alcohol.
  • Use cautiously in children and infants, or in people with osteoporosis, skin disorders, thyroid disorders, affective disorders, or those taking agents for depression.
  • Avoid taking vitamin A in high doses, due to increased risk of toxicity and death.
  • Avoid in combination with tetracycline antibiotics, agents that are toxic to the liver, or retinoids, due to the increased risk of toxic effects.
  • Avoid in people with poor fat absorption, intestinal infections, severe protein energy malnutrition, liver disease, or type V hyperlipoproteinemia (a genetic disorder).
  • High-dose vitamin A and beta-carotene should be avoided in patients at high risk of lung cancer.
  • Vitamin A may increase the risk of bleeding. Avoid use when taking agents that affect bleeding and clotting.
  • Avoid in individuals with a known sensitivity or allergy to vitamin A or any part of the formulation.

Pregnancy and Breastfeeding

  • Vitamin A should only be used within the recommended dietary allowance, because vitamin A excess, as well as deficiency, has been associated with birth defects. Excessive doses of vitamin A have been associated with central nervous system malformations.
  • Vitamin A is excreted in human breast milk. The benefits or dangers to nursing infants are unclear.
  • Tretinoin that is applied to the skin is likely low risk for breastfeeding infants given its poor absorption; however, due to a lack of evidence, caution should be taken to prevent direct skin contact to the nursing infant and only water soluble cream or gel products should be applied.

Interactions

Most herbs and supplements have not been thoroughly tested for interactions with other herbs, supplements, drugs, or foods. The interactions listed below are based on reports in scientific publications, laboratory experiments, or traditional use. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare professional before starting a new therapy.

Interactions with Drugs

  • Vitamin A may increase the risk of bleeding when taken with drugs that increase the risk of bleeding. Some examples include aspirin, anticoagulants (blood thinners) such as warfarin (Coumadin®) or heparin, antiplatelet drugs such as clopidogrel (Plavix®), and nonsteroidal anti-inflammatory drugs such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®).
  • Vitamin A may interfere with the way the body processes certain drugs using the liver's cytochrome P450 enzyme system. As a result, the levels of these drugs may be increased or decreased in the blood and may cause increased or decreased effects or potentially serious adverse reactions. Patients using any medications should check the package insert and speak with a qualified healthcare professional, including a pharmacist, about possible interactions.
  • Vitamin A may cause low blood pressure. Caution is advised in people taking drugs that lower blood pressure.
  • Vitamin A may also interact with agents for depression, agents for diarrhea, agents for lowering cholesterol, agents for the stomach and for intestine disorders, agents for weight loss, agents for worm infections, agents that affect the nervous system, agents that affect the liver, alcohol, antibiotics, anticancer agents, antifungals, antimalarials, antivirals, birth control agents taken by mouth, folate agents, iron salts, mineral oil, nicotine, orlistat, osteoporosis agents (for decreased bone density), phytonadione (vitamin K), retinoids, skin disorder agents, thyroid agents, vaccines, and valproic acid.

Interactions with Herbs and Dietary Supplements

  • Vitamin A may increase the risk of bleeding when taken with herbs or supplements that increase the risk of bleeding. Multiple cases of bleeding have been reported with the use of Ginkgo biloba, and fewer cases with garlic and saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this has not been proven in most cases.
  • Vitamin A may interfere with the way the body processes certain herbs or supplements using the liver's cytochrome P450 enzyme system. As a result, the levels of other herbs or supplements may become too high or too low in the blood. It may also alter the effects that other herbs or supplements possibly have on the cytochrome P450 system.
  • Vitamin A may cause low blood pressure. Caution is advised in people taking herbs or supplements that lower blood pressure.
  • Vitamin A may also interact with antibacterials, anticancer herbs and supplements, antifungals, antimalarials, antioxidants, antivirals, apple pectin, carob, carrageenan, cholesterol-lowering herbs and supplements, fat-soluble vitamins, fiber, folic acid, guar, herbs and supplements for birth control, for bone loss, for depression, for diarrhea, for obesity, for stomach and intestine disorders, and for worm infections, herbs and supplements that affect the nervous system, herbs and supplements that affect the thyroid, herbs and supplements that affect the liver, iron, microcrystalline cellulose, multiple micronutrient supplements, plant stanols and sterols, tobacco, vitamin E, vitamin K, wheat bran, and zinc.

Authors

Selected References

Natural Standard developed the above evidence-based information based on a systematic review of the available scientific articles. For comprehensive information about alternative and complementary therapies on the professional level, go to www.naturalstandard.com. Selected references are listed below.

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  2. Bjelakovic G, Nikolova D, Gluud LL, et al. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane.Database.Syst.Rev. 2012;3:CD007176.
  3. Bremner JD, Shearer KD, and McCaffery PJ. Retinoic acid and affective disorders: the evidence for an association. J Clin.Psychiatry 2012;73(1):37-50.
  4. Cortes-Jofre M, Rueda JR, Corsini-Munoz G, et al. Drugs for preventing lung cancer in healthy people. Cochrane.Database.Syst.Rev. 2012;10:CD002141.
  5. Etminan M, Bird ST, Delaney JA, et al. Isotretinoin and risk for inflammatory bowel disease: a nested case-control study and meta-analysis of published and unpublished data. JAMA Dermatol. 2013;149(2):216-220.
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  7. Girard AW, Self JL, McAuliffe C, et al. The effects of household food production strategies on the health and nutrition outcomes of women and young children: a systematic review. Paediatr.Perinat.Epidemiol 2012;26 Suppl 1:205-222.
  8. Hanson B, MacDonald R, and Shaukat A. Endoscopic and medical therapy for chronic radiation proctopathy: a systematic review. Dis.Colon Rectum 2012;55(10):1081-1095.
  9. Masetti R, Biagi C, Zama D, et al. Retinoids in pediatric onco-hematology: the model of acute promyelocytic leukemia and neuroblastoma. Adv.Ther. 2012;29(9):747-762.
  10. Masset E, Haddad L, Cornelius A, et al. Effectiveness of agricultural interventions that aim to improve nutritional status of children: systematic review. BMJ 2012;344:d8222.
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  12. Wallace A, Ryman T, Mihigo R, et al. Strengthening evidence-based planning of integrated health service delivery through local measures of health intervention delivery times. J Infect.Dis. 2012;205 Suppl 1:S40-S48.
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