Vitamin A is essential for a range of bodily functions, including vision, embryonic development, tissue integrity and immunity.
There are two different types of vitamin A : preformed vitamin A (found in meat, poultry, fish and dairy products) and provitamin A (found in fruits, vegetables and other plant-based products) 1.
Preformed vitamin A is known as the active form and includes the compounds retinol, retinal and retinoic acid; provitamin is the inactive form and includes the compounds alpha-carotene, beta-carotene and beta-cryptoxanthin.
These compounds are converted to the active form in the body.
Vitamin A provides eye protection. Vitamin A plays several important roles in the health and protection of eyes. According to the American Academy of Ophthalmology, to see the full spectrum of light, the eyes need to produce pigments for the photoreceptor cells in the retina to work properly. Vitamin A deficiency stops the production of these pigments, leading to night blindness.
Night blindness (nyctalopia) is the inability to see well at night or in poor light (2).
Vitamin A also plays an important role in nourishing the cornea — the clear, dome-shaped surface that covers the front of the eye and helps with vision focus. Without enough vitamin A, the eyes cannot produce enough moisture to keep the corneas properly lubricated (3,4).
Vitamin A deficiency is the leading cause of preventable blindness in children worldwide.
Vitamin A is being researched for its anticancer benefits. Scientists are studying vitamin A byproducts for their usefulness in cancer therapies, but these treatments are different from extra vitamin A taken in the form of supplements.
Some studies suggest that diets richer in micronutrients including vitamin A can improve immune functioning and the prognosis in head and neck cancer patients. It may also reduce the risk of oral and pharyngeal cancers.
Vitamin A, however, has been shown not to be protective against non-small cell lung cancer or to be effective in prolonging survival for melanoma patients. Some studies show it may actually increase the risk of prostate cancer (5).
Further studies are needed to better understand the relationship between vitamin A levels in the body and cancer risks and benefits.
Vitamin A helps promote a healthy immune system. Vitamin A deficiency impairs immunity by impeding normal regeneration of mucosal barriers damaged by infection, and by diminishing the function of neutrophils, macrophages and natural killer cells.
Vitamin A also plays a role in the development of both helper T cells and B cells. Helper T cells not only help activate B cells to secrete antibodies and macrophages to destroy ingested microbes, they also help activate cytotoxic T cells to kill infected target cells (6,7).
Vitamin A provides various benefits to the skin. To evaluate the effectiveness of topical retinol (vitamin A) in improving the clinical signs of naturally aged skin, researchers performed a study on 36 elderly subjects (mean age, 87 years).
After 24 weeks, it was revealed that there were significant differences between retinol-treated and placebo-treated skin for changes in fine wrinkling scores.
Topical retinol improves fine wrinkles associated with natural aging. Significant induction of glycosaminoglycan, which is known to retain substantial water, and increased collagen production are most likely responsible for wrinkle reduction. With greater skin matrix synthesis (production of compounds that form new skin), retinol-treated aged skin is more likely to withstand skin injury and ulcer formation along with improved appearance (8).
According to The Journal of the American Medical Association, topical tretinoin (a form of Vitamin A that is available by prescription and tends to be more aggressive than retinol) improves photoaged skin.
In a 16-week study, all patients applied topical tretinoin to one forearm and vehicle cream to the other. Half of the patients received tretinoin to the face, and half received vehicle cream. All 30 patients who completed the study showed statistically significant improvement in photoaging on the tretinoin-treated forearms, but not on the vehicle-treated forearms.
Fourteen of the 15 patients who received tretinoin to the face had improvement in photoaging, whereas none of the vehicle-treated patients’ faces improved (9).
Vitamin A helps treat acne. Prescription retinoids, derived from vitamin A, are one of the main forms of acne treatment. For acne, retinoids can be administered topically in a variety of formulations.
When used as directed, this class of medication is well tolerated and very efficacious in managing acne. Furthermore, there is evidence showing its role in improving and preventing atrophic acne scarring — indented scarring that heals below the normal layer of skin tissue (10).
Side effects were limited to irritation of tretinoin-exposed skin.
Vitamin A helps ensure the normal growth and development of embryos. According to the authors of a study published in The Journal of Nutrition, both the lack and excess of vitamin A during embryonic development may result in congenital malformations (11).
Major target tissues of vitamin A deficiency include the heart, central nervous system and structures derived from it, the circulatory, urogenital and respiratory systems, and the development of skull, skeleton and limbs (12).
High amounts of the active form of vitamin A can be toxic. Chronic toxicity is usually associated with chronic intake of more than 30,000 IU of vitamin A, although there have been several cases of significant liver toxicity with vitamin A doses as low as 20,000 IU and in regular alcohol consumers.
Nausea and vomiting, headache, blurred vision, muscular weakness and elevated liver function tests may also occur (13).
A healthy and varied diet will provide most people with enough vitamin A. Topical retinol should be applied as directed by the prescribing physician.
Further studies are needed to determine the proper dosage for the treatment of other conditions.
Vitamin A is a nutrient important for the health of vision, embryonic development, tissue integrity and immunity.
There are two types of vitamin A: preformed vitamin A which is known as the active form and includes the compounds retinol, retinal and retinoic acid; provitamin is the second type and is the inactive form and includes the compounds alpha-carotene, beta-carotene and beta-cryptoxanthin.
Vitamin A is also being researched for its potential role in fighting and preventing certain types of cancer and studies show its efficacy in treating signs of aging and acne.
Researchers warn that high amounts of vitamin A can be toxic.