Vitamin A is an important fat soluble vitamin that is stored in our liver. It can also be called retinyl palmitate, retinol, retinoic acid or retinal depending on whether our body is storing, transporting or using it.
What is it used for?
- It helps us see, especially in low light levels and therefore one of the first symptoms of deficiency is night blindness.
- It also helps our growth and development by boosting or down regulating the activity of our hox genes, which makes it an important part of our early life both as an embryo and then as an infant. It does this by helping our cells decide what types thay are going to be and where they should go.
- It helps our skin condition. Our skin cells (keratinocytes) rapidly turn over, with old ones being removed and new ones being created on a daily basis. In much the same way as vitamin A helps with our growth and development, it switches on genes that boost the growth and development of our skin cells. As such it can be used as a treatment for acne and other skin disorders, although these drugs have been associated with cancer. Eating plenty of vitamin A, would probably be a safer way of improving skin health.
Where does vitamin A come from?
Vitamin A comes from animal sources as pre-formed vitamin A. It is found particularly in the liver and in some cases in toxic amounts. There have been many cases of polar explorers dying as a result of eating polar bear livers, which are a particularly concentrated source of vitamin A. Other than liver, vitamin A is also found in cheese, eggs, butter and cream.
It is also available in the form of beta carotene from yellow, orange and red fruits and vegetables such as carrots, sweet potatoes and spinach. Beta carotene is converted into vitamin A by the body. How much is absorbed and converted from food depends on if and how you cook them. As carotenes are fat soluble they are best absorbed when cooked in oil. If you eat them raw only about 1/12th of the amount will be converted into vitamin A, whereas when cooked in oil as much as 1/2 will be converted. Unlike vitamin A from animals beta-carotene is not dangerous in excess, as the body will not convert it if there is sufficient vitamin A available.
Should I supplement this?
Probably not unless you have good reasons for doing so. Vitamin A is one of the easiest supplements to overdose on. The recommended daily amount from foods is 900ug (micrograms), just under one milligram. Excess vitamin A of the order of 2 times the rda over a long period of time has been linked to reduction in bone density in older adults. Note that the rda was originally set at 1500ug in the US some years ago and this is why many supplements supply this amount. People with kidney stones should avoid supplementation and pregnant women should take care to supplement less than 1500ug/day. An excess is linked to birth defects.
What can cause vitamin A deficiency?
- Vitamin A deficiency is most prevalent in 3rd world countries where fat, protein and zinc intakes may all be low.
- The fat substitue, Olestra, common in the 90's can bind vitamin A in the gut reducing absorption, as can diseases of fat malabsorption such as cystic fibrosis.
- Chronic alcohol consumption depletes liver stores of vitamin A, but also can make the liver oversensitive to vitamin A, leading to toxicity.
This vitamin is vital to health, but it is unusual to need to supplement. If you suffer from night blindness you are best off initially checking that your diet contains plenty of sources of vitamin A. A weekly dish of liver and onions may be the answer, alternatively eating more eggs and cheese, and stir frying sweet potato or carrots slices should help increase your levels.