Vitamin A

Vitamin A has several important functions in the body.

It is a fat-soluble vitamin.

It is also known as retinol.

These include:

• helping the natural defences of your body fight against illness and infection so that they work properly through the immune system work.
• helping you see generally, especially when light is dim
• maintenance of cell function for growth
• keeping the skin, various mucous membranes and the lining of some parts of the body, such as the nose and sexual membranes in good condition

It generally operates as a powerful antioxidant. That means it can prevent or at least reduce the amount of cellular damage caused by oxidative stress. 

Vitamin A deficiency is a major concern for many poor countries with low income levels. 

Good Sources Of Vitamin A

Good sources of vitamin A according to the UK’s NHS include:

• cheese
• eggs
• oily fish like mackerel, pilchards and sardines
• fortified low-fat spreads including most fortified margarines
• milk and yogurt (kefir is a good source).
• liver and liver products such as liver pâté – this is a particularly rich source of vitamin A. You may be at risk of having too much vitamin A if you have it more than once a week (this is particularly important if you’re pregnant).
• Plants which produce beta-carotene include carrots, sweet potatoes, broccoli, spinach, pumpkin, mango and papaya, apricots.

You can obtain vitamin A by including good sources of beta-carotene in your diet, as the body can convert this into retinol (vitamin A).

Nutritional Requirements

The total vitamin A content in food is expressed in micrograms (microg) of retinol equivalents (RE).

An adult aged between 19 and 64 needs:-

• 700 μg (0.7mg) per day for men
• 600 μg (0.6mg) per day for women

The amounts needed however vary throughout life. Breastfeeding women for example need at least 1.2mg per day (NIH).

Safety Issues With Vitamin A

Too much vitamin A in the diet or with supplementation is toxic. It is actually teratogenic at very high doses.

Main Health Benefits

(1) Possible Lowering Of Risk With Certain Cancers

Cancer is disease caused by uncontrolled growth of abnormal cells. There are many different types of cancer. A number of these types have had their risk of occurrence reduced to varying levels through supplementation and through appropriate nutrition. However, considerable research is needed to validate and verify any claims made.

A number of researchers and nutritionists are interested in the key role that vitamin A plays in the growth and development of living cells. Vitamin A may influence cancerous cell formation and suppression.

Some observational studies showed that a higher level of vitamin A in the form of beta-carotene in the diet or as a supplement could decrease the risk of particular cancers.

The main cancer of interest is non-Hodgkin lymphoma (NHL) (Chen et al., 2017). A meta-analysis concluded that  suggest that higher intakes of alpha-carotene, beta-carotene, and lutein/zeaxanthin might protect against NHL development.

An earlier meta-analysis (Tang et al., 2014) found that high vitamin A intakes were also associated with  a lower risk of bladder cancer.

Some anomalies however suggested that smokers taking beta-carotene supplements increased their risk of lung cancer (Omenn et al., 1996). The studies are currently being assessed in greater detail.

An exceptional source of information about vitamin A can be obtained from the National Institutes of Health web-site.

(2) Protecting Our Sight

 Vitamin A is needed for our eyesight especially with night vision. It is a compound contained in the retina which converts light energy into nerve impulses that allow the brain to register shapes and colour.

The compound that retinol is part of is rhodopsin and is very light sensitive. This is a protein containing bound retinol.

The first symptom of a lack of vitamin A is night blindness, also called nyctalopia.

Generally, antioxidant supplements containing vitamins and minerals such as vitamin A will slow the progression of eye conditions like age-related macular degeneration (AMD) (Evans and Lawrenson, 2017). This study did show that lutein and zeaxanthin had little impact on progression of the condition.

One major study, the Age-Related Eye Disease Study, showed supplementation with an antioxidant supplement including vitamin A as beta-carotene and zinc was beneficial.  It showed that giving people over the age of 50 with modest eyesight degeneration the mixed supplement reduced their risk of developing AMD by 25% (AREDS, 2001).

(3) Vitamin A Reduces The Development Of Skin Diseases And Forms Of Acne.

Vitamin A medications are often used to treat acne although how it works is not that clear.

(4) Helps With Bone Health

A lack of this vitamin is said to be associated with poor bone health and an increased risk of fractures (Zhang et al., 2017). The evidence still needs clarifying.

(5) Recovering A Sense Of Smell.

Back in 1962, an article reported that healthy people who lost their sense of smell might recover it if they took vitamin A. Nowadays, vitamin A is available in preparations, available as nasal sprays. Whether this finding has been substantiated remains to be validated but may prove worthwhile for those attempting to help people with nasal lesions

Products Containing Vitamin A

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References

Age-Related Eye Disease Study Research Group (2001). 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. Archives of ophthalmology (Chicago, Ill. : 1960), 119(10), 1417–1436. https://doi.org/10.1001/archopht.119.10.1417 (Article)

Chen, F., Hu, J., Liu, P., Li, J., Wei, Z., Liu, P. (2017) Carotenoid intake and risk of non-Hodgkin lymphoma: a systematic review and dose-response meta-analysis of observational studies. Ann Hematol. 96(6) pp. 957-965. doi:10.1007/s00277-016-2898-1 (Article)

Evans, J.R., Lawrenson. J.G. (2017) Antioxidant vitamin and mineral supplements for slowing the progression of age-related macular degeneration. Cochrane Database Syst Rev.; 7(7):CD000254. Published 2017 Jul 31. doi:10.1002/14651858.CD000254.pub4 (Article)

Omenn, G.S., Goodman, G.E., Thornquist, M.D., et al. (1996) Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N Engl J Med. 334(18) pp. 1150-1155. doi:10.1056/NEJM199605023341802 (Article)

Tang, J. E., Wang, R. J., Zhong, H., Yu, B., & Chen, Y. (2014). Vitamin A and risk of bladder cancer: a meta-analysis of epidemiological studies. World Journal of Surgical Oncology, 12, 130. https://doi.org/10.1186/1477-7819-12-130 (Article)

Zhang, X., Zhang, R., Moore, J.B., et al. (2017) The Effect of Vitamin A on Fracture Risk: A Meta-Analysis of Cohort Studies. Int J Environ Res Public Health. 14(9):1043. Published 2017 Sep 10. doi:10.3390/ijerph14091043 (Article) 

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