Vitamin A doesn't seem to be overly important in that we, in the developed world, appear to be getting enough of it from our diets. However, its still interesting to read about. According to Wikipedia: the term vitamin A refers to a group of unsaturated nutritional hydrocarbons. This includes retinol, retinal and retinoic acid and several pro-vitamin A carotinoids of which beta-carotene is the most important. If you have ever heard the old saying "carrots let you see in the dark", then you're about to find out how this could be true. The beta-carotene mentioned above is present in carrots and when ingested by humans, is converted into vitamin A, an umbrella term specifically encompassing retinal in this respect. The significance of this conversion to retinal with relation to low light vision is that retinal is needed by the eye, specifically the retina, to produce rhodopsin, a light-absorbing molecule. Retinol is essentially the storage form of vitamin A that can be converted reversibly to retinal. The conversion to retinoic acid however, is irreversible and this compound is used for growth and cellular differentiation, it is not used in the retina.
The uses of vitamin A as a whole are the following:
- Growth and development
- Immune system maintenance
- Good vision
- Gene transcription
- Embryonic development and reproduction
- Bone metabolism
- Healthy skin
- Antioxidant properties
- Development of blood cells
- Tissue repair and replacing intestinal lining, this effect can allow vitamin A to prevent intestinal disorders such as irritable bowel syndrome
Signs of a vitamin A deficiency are:
- Stunted growth
- Immune system disorders
- Respiratory infections
The best food sources of vitamin A: are liver, chillis, sweet potatoes, sweet carrots and green vegetables.
According to the World Health Organisation, around 250,000 to 500,000 children become blind due to vitamin A deficiency and around 50% of these children die within a year of this happening.