Vitamin A

What's here? On this page you can discover:

the forms of vitamin A,
what it does for us,
the effects of deficiency,
how to get the most from food sources,
how much you need to stay well,
who may need more,
its likely anti-cancer role, and
warnings of toxicity ...and more.

The forms

The two main forms of vitamin A are:

Retinol and
Beta-carotene

Retinol is the naturally occurring form of vitamin A found in animal products.

Beta-carotene is also called the 'plant' vitamin A. It is a carotenoid which is converted into vitamin A in the liver. Beta-carotene is found in brightly colored fruit and vegetables, such as carrots from which carotene is named.

The functions of vitamin A

Vitamin A plays an important role in many of our body's functions, including:

Our vision, especially in dim light.
Bone growth.
Reproduction, through roles in proper sperm formation and maintaining healthy fetuses in pregnant women.
Cell division and cell differentiation (which is the process by which a cell decides what type of cell it is going to become).
Helping to maintain the surface linings of the eyes and the respiratory, urinary, and intestinal tracts (when these linings break down, bacteria can enter the body and cause infection).
Helping to maintain the skin and mucous membranes so that they act as a barrier to bacteria and viruses.
Helping to regulate the immune system (which prevents or fights off infections by making white blood cells that destroy harmful bacteria and viruses.
Helping lymphocytes (a type of white blood cell that fights infections) to function more effectively.
Serving as antioxidants which protect cells from free radicals (which are potentially damaging by-products of oxygen metabolism that may contribute to the development of some chronic diseases).
Helping to prevent cancer.
Helping to slow the aging process.

The symptoms and signs of vitamin A deficiency

The symptoms of a vitamin A deficiency include:

poor vision (night blindness),
mouth ulcers,
frequent infections,
the scalp may become dry and have dandruff, and
acne may occur.

Vitamin A deficiency can occur:

when vitamin A is lost through chronic diarrhea,
through an overall inadequate intake, as is often seen with protein-calorie malnutrition,
when there is an inadequate intake of protein, calories and zinc (these nutrients are needed to make Retinol which is essential for getting vitamin A from your liver and transporting vitamin A to your general circulation),
when there is also an iron deficiency which limits the metabolism of vitamin A (iron supplements provided to iron deficient individuals can improve vitamin A nutrition as well as iron status), and
when excessive alcohol intake depletes vitamin A stores (diets high in alcohol also usually do not provide recommended amounts of vitamin A).

Food sources of vitamin A

Vitamin A is found in animal foods such as whole eggs, whole milk and liver.

Carotenoids are found in darkly colored fruits and vegetables.

What Destroys Vitamin A?

Vitamin A can be destroyed by:

cooking, particularly when using copper or iron cooking utensils,
exposure to light and air (some is lost),
soaking in water for some time,
preservatives used in some processed meats (lowers its vitamin A content), and
some vitamin A is lost in the fat during frying.

To retain vitamin A in food:

serve fruits and vegetables raw whenever possible,
keep vegetables (except sweet potatoes and winter squash) and fruits covered and refrigerated during storage,
wash fruit and vegetables just before using them, and
steam vegetables and braise, bake, or broil meats instead of frying.

How much vitamin A do we need?

Recommended Dietary Allowances for vitamin A in micrograms (mcg) Retinol Activity Equivalents (RAE) and International Units (IUs) for children and adults

**Recommended Dietary Allowances**
Age (years)	Children	Men	Women	Pregnancy	Lactation
1-3	300 mcg or 1000 IU
4-8	400 mcg or 1333 IU
9-13	600 mcg or 2000 IU
14-18		900 mcg or 3000 IU	700 mcg or 2330 IU	750 mcg or 2500 IU	1200 mcg or 4000 IU
19 +		900 mcg or 3000 IU	700 mcg or 2330 IU	770 mcg or 2565 IU	1300 mcg or 4335 IU

For infants, Adequate Intake for vitamin A in micrograms (mcg) and International Units (IU) is shown in the small table below.

Note that there is insufficient information to establish a RDA for vitamin A for infants. An adequate intake (AI) has been established that is based on the amount of vitamin A consumed by healthy infants who are fed breast milk.

**Adequate Intake For Infants**
Age (months)	Males and Females
0 to 6	400 mcg or 1330 IU
7 to 12	500 mcg or 1665 IU

It is very important for anyone who consumes excessive amounts of alcohol to include good sources of dietary vitamin A. However, Vitamin A supplementation may not be recommended for individuals who abuse alcohol because alcohol may increase any liver toxicity associated with the excess intakes of vitamin A.

Who may need extra vitamin A to prevent a deficiency?

The World Health Organization (WHO) and the United Nations International Children's Emergency Fund (UNICEF) have issued a joint statement about vitamin A and children's health. Both agencies recommend vitamin A supplements for:

All children diagnosed with measles in communities where vitamin A deficiency is a serious problem and where death from measles is greater than 1%.

In 1994, the American Academy of Pediatrics recommended vitamin A supplementation for:

Children 6-24 months of age who had been hospitalized with measles and hospitalized children older than 6 months.

Other people who may need vitamin A supplements include people with:

Fat malabsorption that can lead to diarrhea and prevent normal absorption of vitamin A.
Cystic fibrosis, sprue, pancreatic disorders, and after stomach surgery; and
Vegetarians who do not consume eggs and dairy foods need greater amounts of provitamin A (carotenoids) to meet their needs.

Vitamin A, beta carotene and cancer

Vitamin A (and in particular beta carotene) has recently been identified as a powerful antioxidant and therefore anti-carcinogen.

There is evidence that a higher intake of green and yellow vegetables or other food sources of beta-carotene and/or vitamin A may decrease the risk of lung cancer, bladder cancer and skin cancers associated with excessive exposure to sunlight. However, the studies on this are still not entirely conclusive.

Vitamin A toxicity

Questions have been raised concerning the toxicity of vitamin A, which is known to be concentrated in the liver.

Symptoms of vitamin A excess include:

hair loss,
headaches, dizziness and blurred vision,
gastrointestinal disturbances (such as nausea and diarrhea),
skin inflammation and itchiness, and
poor muscular coordination and possibly reduced bone mineral density.

Toxic symptoms can also arise after consuming very large amounts of vitamin A over a short period of time.

Beta-carotene does not cause toxicity.

Pregnant women and those planning pregnancy should not take in excess of 7,500 IU of vitamin A per day because of the risk of birth defects. Also avoid eating animal livers because of the high concentration of vitamin A in livers.

Over the past 15 years, synthetic retinoid has been prescribed for acne, psoriasis, and other skin disorders and is considered an effective anti-acne therapy. At very high doses, however, it can be toxic, which is why this medication is usually saved for the most severe forms of acne.

The most serious consequence of this medication is birth defects. It is extremely important for sexually active females who may become pregnant and who take these medications to use an effective method of birth control. Women of childbearing age who take these medications are advised to undergo monthly pregnancy tests to make sure they are not pregnant.

More of this vitamin is required when:

you consume alcohol,
you are on a low-fat diet, or have a diet high in polyunsaturated fatty acids,
if you smoke or live in a polluted area.

It may also be indicated if you suffer from diabetes or have an under-active thyroid gland. Be careful using vitamin A in pregnancy.

It is a good idea to take vitamin A with vitamins E, B group and C, choline, essential fatty acids, calcium, phosphorus and zinc for the best results.

References

Bland, J. 1996, Contemporary Nutrition. J & B Associates.

Davies, S. and A. Stewart., 1997, Nutritional Medicine. Pan.

Holden, S., Hudson, K., Tilman, J. & D. Wolf, 2003, The Ultimate Guide to Health from Nature. Asrolog Publication.

Pressman, A. and S. Buff, 2000, The Complete Idiot's Guide to Vitamins and Minerals. (2nd Ed.) Alpha Books.

Soothill, R. 1996, The Choice Guide to Vitamins and Minerals. A Choice Book Publication.

Sullivan, K. 2002, Vitamins and Minerals: A Practical Approach to a Health Diet and Safe Supplementation. Harper Collins.