Vitamin A is a fat-soluble micronutrient recognized for its importance in proper immune-system functioning and as an antioxidant. It is also known as retinol because it is an alcohol and is involved in the function of the retina of the eye. Beta-carotene and other carotenoids are provitamin forms of vitamin A which are typically found in plants and have vitamin A activity once they are converted in the body by the liver. This conversion depends on protein status, thyroid hormones, zinc, and vitamin C. Conversion will only occur when the body is in need of vitamin A.
The following foods have the highest concentration of Vitamin A. For a more expansive list on food sources of specific nutrients visit Health Canada's Dietary Reference Intakes for Vitamins or USDA's National Nutrient Database
- Vitamin A, Other food sources include:
- Beta-carotene - green plants, carrots, sweet potatoes, squash, spinach, and green peppers
Generally, the more intense the green colour of the plant is, the more beta-carotene is present; the more intense the orange colour is, the more pro-vitamin carotenoids are present.
- Growth and Development: Vitamin A is important for cellular growth and differentiation as well as gene expression. It is extremely important for the epithelium of the oral cavity, respiratory tract, urinary tract, and ducts of the secretory glands.
- Women's Conditions:
- Reproduction: Beta-carotene in particular is very important for proper functioning of the corpus luteum and therefore proper ovulation. Without proper corpus luteum functioning, progesterone levels will not be adequate; this is one of the characteristics of infertility and irregular menstrual cycles. An increase in estrogen to progesterone ratio can also increase risk of ovarian cysts, PMS, fibrocystic breast, and breast cancer.
- Cervical Dysplasia: Beta-carotene is used in the treatment of cervical dysplasia.
- Vaginal Candidiasis: Low tissue levels of beta-carotene is associated with vaginal candidiasis. High dietary intake of beta-carotene may be protective.
- Infertility: Lycopene is a carotenoid which concentrates in the testes and seminal plasma. Low levels are associated with male infertility due to subsequent excessive free radical damage.
- Prostate Cancer: Lycopene is also speculated to have a role in preventing prostate cancer, can lower PSA levels, and reduce DNA damage in white blood cells and prostatic tissue.
- Carotenes as Immune-Enhancing Agents: Independent of their vitamin A activity, carotenes are powerful immune-enhancers.
- Viral Illness: Vitamin A is crucial for immune-system functioning and is further depleted during illness
- Measles: Vitamin A supplementation reduces infant mortality from measles by 50% in the third world; also indicated for seemingly well-nourished children as 50% are also vitamin A deficient.
- Infants with RSV Infection: Children with RSV have low serum vitamin A levels; the lower the level of vitamin A, the more severe the disease.
- AIDS: Vitamin A deficiency (common in HIV and AIDS) is associate with decreased levels of circulating helper T-cells. Beta-carotene is the preferred form.
- Skin Conditions: Effective in treating conditions of hyperkeratosis such as acne, psoriasis, ichthyosis, lichen planus, Darier's disease, palmoplantar keratoderma, and pityriasis rubra pilaris
- Eye Conditions: Dry eyes (topical vitamin A reverses the underlying cellular changes causing dry eyes), cataracts, vision (also important are other antioxidants and zinc)
|Article||Supplemental Vitamin A May Reduce Risk of Melanoma, NMJ, , 2012 August|
- Cancer Prevention: Carotene, more than vitamin A, is a powerful antioxidant, has immune-potentiating activity and is anticarcinogenic.
- Prevention of cardiovascular disease: Due to its antioxidant capabilities, beta-carotene may inhibit damage to cholesterol and the lining of the arteries.
- Carotenes in the Treatment of Photosensitivity Disorders: Beta-carotene is the treatment of choice.
- Osteoporosis: Lycopene can reduce bone loss.
- Immune System Abnormalities: more susceptible to infections such as measles, chicken pox, respiratory syncytial virus (RSV), AIDS, and pneumonia
- Follicular Hyperkeratosis: goose-bump appearance typically seen on back of upper arm
- Night Blindness
- Xerophthalmia: over-arching term to describe eye-related manifestations of vitamin A deficiency, blindness being the most severe
- dry, fissured skin
- brittle nails
- cheilosis (chapped lips)
- prolonged toxicity can lead to bone fragility and thickening of long bones.
First significant sign of toxicity is headache, followed by fatigue, emotional lability, and muscle and joint pain.
Common Deficiency Test: 
- Vitamin A Blood Test - a low level indicates a deficiency.
- Natural vitamin A comes in two forms, retinol and retinyl-palmitate. To increase absorption, the vitamin is either made into micelles or emulsified so that it can be mixed with water. Regular vitamin A is absorbed at a rate of 80-90%.
- There are three main sources of Beta-carotene, synthetic all-trans Beta-carotene, beta- and alpha-carotene from the algae Dunaliella, and mixed carotenes from palm oil. Beta-carotene from palm oil appears to be the best as it gives the best antioxidant protection and is absorbed 4-10 times better than synthetic forms .
- The recommended dosages varies based on age and health status. To determine what your specific requirements are talk to your naturopathic doctor or other trained medical professional.
- Infants (under 1 year): 1875 I.U.
- Child: 2000 I.U. (1-3 years); 2500 I.U. (4-6 years); 3500 I.U. (7-10 years)
- Adult: 5000 I.U. (Males, 11+ years); 4000 I.U. (Females 11+ years)
- Pregnancy and Lactation: 4000 I.U.
- An I.U. (International Unit) is defined as 0.3 micrograms of crystalline retinol or 0.6 micrograms of beta-carotene.
Therapeutic supplementation should only be done under the supervision of a naturopathic doctor or other trained health practitioner.
- Children: Single large doses can cause acute toxicity in children (intracranial pressure, vomiting, headache, joint pain, stupor, occasionally papilledema - inflammation and edema of the optic nerve).
- Adults: Single large doses can cause toxicity (>50,000 I.U.) or smaller daily doses if there are storage and transport issues (as seen in liver cirrhosis, hepatitis, and protein-energy malnutrition)
- Seniors: Lower doses are generally recommended
- Pregnancy: Avoid supplementation during pregnancy. If at risk of becoming pregnant, keep supplementation low or consider carotenes.
- Breastfeeding: Limit vitamin A in nursing HIV-infected mothers or those susceptible to pregnancy.
- Other populations at risk of toxicity: Smokers - Beta-carotene supplementation in this population puts an individual at higher risk of developing lung cancer; diabetics and individuals with liver disease; individuals with genetic predisposition to hypercholesterolemia.
Beta-carotene is not associated with the same toxicity issues as vitamin A as the body will only convert beta-carotene to vitamin A if it is needed.
- Contraindications: compromised liver, hepatitis, or liver disease; alcoholism can cause a vitamin A deficiency but Retinol and ethanol react to increase oxidative stress and increase the risk of hepatotoxicity.
Drug interactions include:
- Supportive or Beneficial:
- Antacids - Co-administration of vitamin A exerts cytoprotective effect and enhances healing of gastric ulcers.
- Anthelmintic Drugs - Co-administration can reduce symptoms of intestinal parasites while supporting epithelial integrity and immune system.
- Chemotherarpy and Related Cytotoxic Agents - Co-administration is appropriate in some cases.
- Corticosteroids (oral) - Concomitant use may enhance drug efficacy. Supplement during and after extended steroid administration.
- Addresses Drug-Induced Deficiency:
- Cholestyramine, Colestipol, and Related Bile Acid Sequestrants - Drug tends to reduce absorption and assimilation of vitamin A and other fat-soluble vitamins.
- Colchicine - Drug impairs vitamin A absorption.
- Methyltestosterone - Drug may impair visual function by altering serum levels and metabolism of vitamin A and Beta-carotene. Discontinuation of drug might be necessary.
- Mineral Oil - Oil may cause malabsorption of fat-soluble vitamins such as vitamin A. Take vitamin and mineral supplements at least 2 hours before or after oil.
- Neomycin - Drug may impair vitamin A absorption.
- Orlistat (Xenical) - Drug may impair vitamin A absorption and other fat-soluble nutrients.
- HMG-CoA Reductase Inhibitors - Drug may elevate serum Retinol levels.
- Medroxyprogesterone - Drug may elevate serum Retinol levels and supplementation may need to be avoided. Carotenoids may be indicated.
- Oral Contraceptives - Avoid Retinol administration at high doses especially with compromised liver function. Carotenoid support may be indicated.
- Tetracycline Antibiotics - Concurrent use of vitamin A/retinoids and tetracycline antibiotics is associated with severe adverse effects such as headaches, pseudotumor cerebri (benign intracranial hypertension).
Nutrient interactions include:
- Vitamin E and zinc are particularly important for proper function of vitamin A. Deficiencies in zinc, vitamin C, protein, or thyroid hormone can impair the conversion of pro-vitamin carotenoids to vitamin A.
- Calcium - Excessive vitamin A intake can lead to bone loss, therefore concomitant administration of calcium with vitamin D is encouraged with high-dose administration of retinoids.
- Iron - Vitamin A deficiency can exacerbate iron deficiency anemia.
- Vitamin D - Vitamin A may antagonize the action of vitamin D.
- Vitamin E - Large doses of vitamin E can interfere with absorption of vitamin A.
- Zinc - Deficiency in zinc interferes with vitamin A metabolism (absorption, transport, utilization).
- Medlineplus 
- Murray Michael T (2005) Encyclopedia of Nutritional Supplements, The Essential Guide for Improving Your Health Naturally, Prima Publishing
- Hoffer Abram, Prousky Jonathan (2006) Naturopathic Nutrition, a Guide to Health Food and Nutritional Supplements, CCNM Press
- Bralley J Alexander and Lord Richard S (2005) Laboratory Evaluations in Molecular Medicine, Nutrients, Toxicants, and Cell Regulators Institute for Advances in Molecular Medince, GA
- Stargrove Mitchell Bebell, Treasure Jonathan, McKee Dwight L (2008) Herb, Nutrient, and Drug Interactions, Clinical Implications and Therapeutic Strategies. Mosby