Vitamin A - The Basics
Vitamin A is made up of retinol, retinal and four
carotenoids which are the dietary precursors of retinol. It is
needed by the eye to form retinal which is necessary for both
low-light and colour vision. It also plays other roles within
the body as a growth factor, much like a hormone.
Adequate intake of Vitamin A is required for eyesight, skin health,
as an antioxidant, bone metabolism, immune function and much more.
Where do I get Vitamin A from?
Vitamin A can be consumed from animal and vegetable
sources. In animal sources it is consumed directly as retinol
whereas in vegetable sources it is consumed in one of the carotenes,
which the human body is able to convert into retinol.
Herbivores
and omnivores are able to convert carotenes to retinol but pure
carnivores cannot. So a lion fed on nothing but carrots would,
apart from getting very angry, go blind.
Vitamin A is found in significant quantities in a broad variety of
animal foods such as liver, cheese, egg and milk as well as a broad
variety of vegetables and fruits, including carrot, broccoli, sweet
potato, spinach, pumpkin, apricots, mangoes and melons.
How much Vitamin A do I need?
Recommended dietary intakes of Vitamin A depend on age, sex and
other factors. The Australian National Health Recommendations are as
follows:
| |
Age |
RDI in micrograms |
| All |
0-6 months |
250 |
| |
7-12 months |
430 |
| |
1-3 years |
300 |
| |
4-8 |
400 |
| Boys |
9-13 |
600 |
| Males |
14+ |
900 |
| Females |
14+ |
700 |
Pregnant and lactating women will require more than this. Read
more
here.
It is possible to over consume Vitamin A as retinol. The body
stops metabolising retinol from beta-carotene when it has enough Vitamin
A, but direct and extreme over ingestion of retinol can be fatal. Upper
recommended levels
for healthy adults are 3000mcg.
It may be that the body can handle much more than this, but it is of no
benefit above these levels so the National recommendations suggest that
intake be limited to this.
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