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Vitamin A is a term for a number of related compounds, the main one being pre-formed vitamin A which is technically called Retinol. However, some of the pigments or colour found in plants can be used by the body to make vitamin A. These are called carotenoids such as Alpha-carotene and Beta-carotene. Around 50 of the 600 carotenoids are able to be converted in this way but Beta-carotene is the largest and best studied. Hence you’ll sometimes see it called pro-vitamin A.
Vitamin A occurs both as Retinol and Beta-carotene (which is converted into Retinol in the body) in fruits, vegetables and oils,.
What does Retinol do in the body?
Retinol or vitamin A is a fat-soluble vitamin which helps maintain normal reproduction, vision and immune function. Specifically it is involved in:
- Eyesight - protects against night blindness
- Normal growth in children
- Healthy skin and mucous membranes
- Resistance to infection such as colds and flus.
How much Retinol do I need?
The Recommended Dietary Intake (RDI*) for vitamin A as Retinol Equivalents each day is:
300mcg (1-3 yrs)
400mcg (4-8 yrs)
600mcg (9-13 yrs)
700mcg (girls 14-18 yrs)
900mcg (boys 14-18 yrs)
700 mcg or 2,300 IU (women)
900 mcg or 3,000 IU (men)
800mcg and 700mcg for young mothers aged 14-18 yrs
1,100mcg or 3,666 IU for all ages
Conversion: 1 IU is equal to 0.3 Retinol Equivalents.
1μg Retinol Equivalents = 6μg beta-carotene
mcg or μg = micrograms which is one-thousandth of a milligram
Safe upper limit:
3,000 micrograms or 10,000 IU a day
High doses of Retinol in pregnancy can cause birth defects and must be avoided.
During pregnancy, when high intakes can harm the unborn baby, the upper limit is still set at 3,000 mcg or 2,800mcg for young mothers aged 14 to 18 years.
My top 12 best food sources of vitamin A
Retinol is found in animal-derived foods in the fatty parts. Here’s my top 12 richest food sources by weight per 100g or 3 ½ oz in descending order :
1. Lamb liver (lamb’s fry) cooked
2. Beef liver, cooked
3. Chicken livers, cooked
4. Pate, liverwurst
5. Kangaroo, cooked
6. Oily fish such as eel (fish liver oils are very rich e.g. cod liver oil)
9. Margarine/Spread (it is added)
11. Egg yolk
12. Cheese, Brie or Camembert
Source: AUSNUT 2011-13
Don’t forget that Beta-carotene is also converted into Retinol once in the body. So carrots and green vegetables contribute to vitamin A. See here for more.
Vitamin A and fat
Because vitamin A is a fat-soluble vitamin, it relies on dietary fat for its absorption. It is stored in the body, primarily in the liver, and toxicity can occur with high doses of Retinol, but not carotenoids.
High doses of Retinol in pregnancy can cause birth defects and should be avoided. Carotenoids in food, but not Retinol, have been shown to have powerful antioxidant functions in the body.
One of the first signs of vitamin A deficiency is night blindness, an inability to see well in dim light. Vitamin A deficiency blindness is the commonest form of preventable blindness worldwide but mainly affects young children and pregnant women in low-income countries where rice, devoid of Beta-carotene, is the staple food.
It is rare in Australia and other developed countries where it mainly affects those who have trouble absorbing the vitamin, have fat malabsorption or have liver disorders. Interference with absorption or storage is likely in coeliac disease, cystic fibrosis, pancreatic insufficiency, duodenal bypass, chronic diarrhoea, bile duct obstruction, giardiasis and cirrhosis.