Vitamin A Supplements Review, Including Beta-Carotene and Cod Liver Oil
Initial Posting: 10/20/18 Last update: 8/6/2019
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Summary: What You Need to Know About Vitamin A Supplements
What It Is:
- How much do you need to take? Unless you're deficient in vitamin A or have a condition that can cause deficiency, you probably don't need to take a vitamin A supplement. Americans are more likely to get too much vitamin A from their diets than too little. The daily requirement for vitamin A is 900 mcg (or 3,000 IU in the retinol form) for men, 700 mcg (2,333 IU) for women, and is lower for children.
- Changing labels – Be aware that supplement labels are in the process of being updated to show vitamin A in "mcg" (micrograms) of retinol activity equivalents - RAE. This is more scientifically correct than the older "IU" format. For reference, 900 mcg = 3,000 IU of vitamin A as retinol or 6,000 IU of beta-carotene, since retinol (and related retinyl forms) have greater biological activity than beta-carotene.
- How much is too much? Too much vitamin A (for adults, over 3,000 mcg RAE daily -- or 10,000 IU in the retinol form) can cause problems, and is of particular concern for women who are pregnant. Although safe when consumed from fruits and vegetables, there are some concerns with taking beta-carotene, which is converted, as needed, to vitamin A in the body.
- Is cod liver oil better than synthetic vitamin A? The vitamin A in fish oil is the same as the synthetic vitamin A in most supplements -- retinyl palmitate, so it doesn't matter which you use. Cod liver oil tends to cost more but can provide significant amounts of vitamins D and E as well as omega-3 fatty acids (EPA and DHA).
- Best choices? Among the supplements that passed testing, we selected those that provide the best quality and value as our Top Picks, including selections for an overall vitamin A supplement (including optional selections for very high dose vitamin A and fish-free vitamin A), as well as for vitamin A from beta-carotene and from cod liver oil.
Vitamin A is a fat-soluble vitamin necessary to maintain good vision and skin, and important to the immune system. In supplements, "vitamin A" usually refers to its "preformed" or retinol forms (including retinyl palmitate and retinyl acetate) as well as beta-carotene. Preformed vitamin A is found in animal-derived foods, primarily liver and dairy products. Cod liver oil and other fish liver oils are excellent sources of vitamin A, while traditional fish oil supplements (from the oil in fish meat) are not.
Beta-carotene is a member of the carotenoid family of orange, red and yellow pigments, and the most common carotenoid found in fruits and vegetables. It is an antioxidant that protects cells against damage from unstable oxygen molecules called "free radicals." Beta-carotene is referred to as pro-vitamin A; it is converted in the body to vitamin A based on the body's need for vitamin A. This makes beta-carotene a safer form of vitamin A by reducing the risk of vitamin A overdose, although some risks remain (See Concerns and Cautions). Beta-carotene also has other activities in the body independent of its conversion to vitamin A.
Beta-carotene is found in fruits, vegetables and other foods. Rich food sources include apricots, carrots, collard greens, kale, spinach, squash, sweet peppers and sweet potatoes.
What It Does:
Vitamin A (preformed - as retinol)
Vitamin A is used to treat people with vitamin A deficiency, which can cause night blindness, dry skin, and increased risk of infection. It may also cause loss of taste (Bromley, Am Fam Physician 2000). Vitamin A deficiency is rare in the general population in the U.S. where, according to the CDC 2012, less than 1% of the population is deficient and 2% is actually at-risk for excess vitamin A (including 4.8% of older adults). Vitamin A deficiency can occur when there is liver disease, malabsorption, or severe malnutrition. In malnourished women, vitamin A can reduce pregnancy-related night-blindness and death as well as post-delivery diarrhea and fever. In vitamin A-deficient children, vitamin A supplements seem to improve the treatment of HIV-related diarrhea, malaria, and measles. For these reasons, vitamin A supplementation has become particularly important in developing countries.
One study showed that high doses of vitamin A plus vitamin E enhanced healing rate and vision improvement after photorefractive keratectomy (PRK) laser eye surgery to correct near-sightedness (Vetrugno, Br J Opthalmol 2001). Increased vitamin A in the diet has been associated with reduced risk of cataracts, but it is not known if the same is true with vitamin A supplements (Cumming, Ophthalmology 2000).
There is mixed evidence regarding the use of vitamin A to reduce the risk of cancer. Early research suggested that oral supplementation with pre-formed vitamin A (but not beta-carotene) may improve survival among people with lung cancer (Pastorino, J Clin Oncol 1993). However, a more recent review of the research found little benefit from supplementing with naturally occurring vitamin A in people with lung cancer, although there was some benefit with a synthetic analogue, rexinoid bexarotene (Fritz, PLoS One 2011). Population studies suggest that vitamin A (both pre-formed and beta-carotene) might reduce the risk of breast cancer (Zhang, J Natl Cancer Inst 1999), but these results need to be confirmed by human studies looking at the effects of vitamin A supplements.
Vitamin A together with beta-carotene has not been found to prevent colorectal, esophageal, pancreatic or stomach cancers. And vitamin A alone does not prevent ovarian cancer. However, one review of human studies found that antioxidants (including beta-carotene and vitamin A) do not interfere with, and may enhance, the effects of cancer treatments (chemotherapy and/or radiation) and reduce their side effects.
Vitamin A may reduce the risk of melanoma, a deadly skin cancer. A large study found that adults (ages 50 to 76) taking vitamin A supplements had a 40% lower risk of developing melanoma over an average of 6 years than adults not supplementing with vitamin A (Asgari, J Invest Dermatol 2012). Melanoma risk reduction was greater for locations on the head and limbs (areas associated with greater sun exposure) than on the trunk. The protective effect was strongest and most statistically significant among women. The effect was seen only among people taking 4,000 IU or more of vitamin A (as retinol) daily, and not among those getting lesser amounts of vitamin A from multivitamins. There was no association of melanoma risk with intake of carotenoids (e.g., beta-carotene) or intake of vitamin A from foods.
With regard to squamous cell carcinoma, adults with the highest intakes (about 21,691 IU daily) of vitamin A (as retinol and carotenoids including beta-carotene) had a 17% lower risk of developing this skin cancer compared to those with the lowest intakes (about 6,808 IU daily). The study tracked more than 120,000 women and men over approximately 27 years. However, unlike melanoma (discussed above), the apparent benefit was largely driven by dietary, rather than supplemental, intake: Higher intakes of vitamin A from foods alone were associated with a 14% decrease in cancer risk (Kim, JAMA Dermatol 2019).
A small study of children ages 4 to 6 in China with an autism spectrum disorder (ASD) found that they had significantly lower blood levels of retinol than those who did not have an ASD (average level of 0.54 µmol/L vs. 0.82 µmol/L, respectively). The children with ASDs were subsequently given a single, large dose of vitamin A (200,000 IU). When tested again six months later, average blood levels of retinol had increased to 0.79 µmol/L and significant improvements were noted on the overall score and specific measures of the childhood autism rating scale (CARS): relating to people, adaptation to change, anxiety, and verbal and non-verbal communication. However, the study lacked a placebo control group, making it impossible to know if these changes were not random. Blood levels of serotonin (which have been found in other studies to be elevated in children with ASDs) were found to be significantly higher in the children with ASDs compared to those without ASDs, and these levels significantly decreased after vitamin A supplementation (Guo, Brain Res Bull 2017). A study in the U.S. found that children with ASDs between 4 to 8 years of age consumed, on average, less than the recommended daily intake of vitamin A, while younger children tended to consume excessive amounts (i.e., above the UL) (Hyman, Pediatrics 2012).