Vitamin A

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Vitamin A belongs to a group of fat soluble chemical compounds known as retinoids and provitamin A carotenoids such as beta-carotene. Carotenoids are believed to exert powerful antioxidant activity which protects the cells from free radical damage and oxidative stress. Vitamin A is found as retinol in liver (including fish liver), eggs and dairy products. Beta -carotene is found in green, orange and yellow fruits and vegetables, and dairy products. Beta carotene is converted into Retinol inside the body. It is sometimes referred to as ‘Pro-collagen vitamin A’. The Recommended Daily Amount (RDA) in the UK is 900 mcg for males and 700mcg for females.

What is it needed for?

Vitamin A is needed for healthy skin and hair. It is also necessary for the maintenance of  healthy membranous tissue all over the body (i.e. linings of lungs, eyes, vagina, bladder, urinary tract and the digestive system). Vitamin A is an important antioxidant which protects against pollution, stimulates immune function and boosts resistance to infections. It is needed for good vision, especially night vision and is involved in the normal growth of bones and tissues.

Deficiency

Vitamin A deficiency can lead to night blindness, poor growth, impaired hearing, taste and smell, increased susceptibility to infection and reduced male fertility. In pregnancy, vitamin A deficiency can result in malformations in offspring. Deficiency in the developed world is usually limited to those with absorption difficulties, increased susceptibility to infections, chronic liver disease and those who are alcohol dependant.

Evidence

Cancer– Research has shown that higher intakes of carotenoids is associated with a lower risk of lung cancer which was demonstrated in several prospective and retrospective studies of current and former smokers as well as non- smokers (1,2). Research has also shown an association between the intake of vitamin A and the incidence of prostate cancer. In the Carotene and Retinol Efficacy Trial (CARET), subjects who took daily supplements of beta-carotene and retinyl palmitate were shown to have a 35% lower risk of nonaggressive prostate cancer than men not taking the supplements (3).

Age-related macular degeneration (AMD)-. This is believed to be attributed to the role of antioxidants in conditions involving the accumulation of oxidative stress, a characteristic which is typical of AMD.  It is thought that Lutein and zeaxanthin, in particular, accumulate in the retina, the tissue in the eye that is damaged by AMD. One of the largest AMD clinical trials to date known as ‘The Age-Related Eye Disease Study (AREDS)’ has reported on the role of specific nutrients to treat and prevent AMD. In this study it was found that the risk of developing advanced AMD in predisposed individuals was considerably reduced by 25% when supplemented with a combination of beta-carotene (15 mg), vitamin E (400 IU dl-alpha-tocopheryl acetate), vitamin C (500 mg), zinc (80 mg), and copper (2 mg) for 5 years compared to participants taking a placebo (4).

Immunity- Vitamin A is involved in immune function, namely reducing the rate and occurrence of measles, and of respiratory and possibly HIV infections (5).

Our take on how Vitamin A may help you based upon EU approved claims;

Colds, flu and Infections- Vitamin A contributes to the normal function of the immune system- this makes it a popular supplement for those looking to ward off colds, flu and other infections. Vitamin A contributes to the maintenance of normal mucous membranes- It may also help build resistance to respiratory diseases and shorten the duration of diseases due to its role in the maintenance of normal mucous membranes.

Acne, Eczema and Psoriasis– Vitamin A contributes to the maintenance of normal skin which makes it potentially useful for skin problems such as acne, eczema and psoriasis, as a deficiency may lead to poor maintenance of normal skin.

Anaemia– Vitamin A contributes to normal iron metabolism. Vitamin A deficiency could aggravate the condition anaemia-the result of an iron deficiency, therefore including Vitamin A in your diet and if necessary, a supplement- may help to guard against this.

Healthy Vision– Vitamin A contributes to the maintenance of normal vision- taking a supplement containing Vitamin A may help to prevent or delay the degenerative conditions such as Age Related Macular Degeneration.

Safety and side effects

Vitamin A is fat soluble and is stored in the body (predominantly in the liver) in excess amounts. Due to the potential accumulation of vitamin A in the body it can be toxic if taken in high amounts over a certain period of time. However, large amounts of beta-carotene and other provitamin A carotenoids are not associated with major adverse effects. The Tolerable Upper Intake Level for Vitamin A for adults in the UK is 3000ug (mcg) per day.

References

  1. Johnson EJ, Russell RM. Beta-Carotene. In: Coates PM, Betz JM, Blackman MR, et al., eds. Encyclopedia of Dietary Supplements. 2nd ed. London and New York: Informa Healthcare; 2010:115-20.
  2. Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington, DC: National Academy Press; 2000
  3. Neuhouser ML, Barnett MJ, Kristal AR, Ambrosone CB, King IB, Thornquist M, et al. Dietary supplement use and prostate cancer risk in the Carotene and Retinol Efficacy Trial. Cancer Epidemiol Biomarkers Prev 2009;18:2202-6.
  4. Age-Related Eye Disease Study Research Group. A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta carotene, and zinc for age-related macular degeneration and vision loss: AREDS report no. 8. Arch Ophthalmol 2001;119:1417-36.
  5. Gerster H: Vitamin A–functions, dietary requirements and safety in humans; Int J Vitam Nutr Res. 1997;67(2):71-90. Review. PMID: 9129249.