Vitamins can be defined as organic high molecular mass compounds required in relatively small amounts for normal body function. The human body has lost the ability to synthesise vitamins and hence we need these compounds in our diet. However, it is worth noting that vitamin D is produced by the skin in response to sunlight, both biotin and vitamin K are produced by the activities of gut bacteria, and niacin (vitamin B3) can be synthesised from tryptophan, an essential amino acid frequently found in the diet. Shortage of these vitamins therefore seems unlikely in even the most chaotic of diets!
Other animals have different vitamin requirements; for example, most mammals have no need of vitamin C, as they produce their own. Hence vitamin C is found in small amounts in milk and fresh meat, although it is quickly destroyed by heating. Primates, guinea pigs and bats all need this vitamin in their diet, and so they learned to eat fruit and vegetables as part of their diet.
A Quick History
Early in the 20th century, it was found that there were essential dietary ingredients in both the fatty and water-based components of milk. The former was called "Factor A", (vitamin A), the latter "Factor B" (vitamin B). It was soon realised that vitamin B was a mixture of chemical compounds known as amines, hence the term vitamin or "vital-amine". The naming of the vitamin B complex progressed sequentially, B1, B2, B3, B6, B12 etc., but there were gaps which reflected duplications or errors. The naming of other vitamins progressed alphabetically for a while, with vitamins C, D, E and K surviving scrutiny to the present day.
Fat Soluble or Water Soluble?
This is the key to their occurrence, metabolic function and toxicity. Vitamins A, D, E and K are fat soluble and found widely in dairy products and meat, with vitamin E found mainly in vegetable oils and eggs. Plants such as carrots and peppers contain the yellow/orange pigment beta-carotene, which the body converts to retinol, so an aversion to dairy produce need not compromise vitamin A intake. The functions of these vitamins deserve closer study:
Water-soluble vitamins include all the vitamins in the B group, vitamin C, biotin, folate and pantothenic acid. These are found in a wide variety of plant and animal based foods, although vitamin B12 is not found in plants, and is a potential shortfall in the diet of strict vegetarians, unless supplemented foods are included.
The best source of all these vitamins will always be a balanced diet. Supplements are a useful stand-by when meals are badly planned or missing. Athletes and body builders may need extra supplements, but beware the marketing ploy which suggests that "more is better." Our bodies have been handling our vitamins requirements a lot longer than the editors of nutrition and food magazines!
Other animals have different vitamin requirements; for example, most mammals have no need of vitamin C, as they produce their own. Hence vitamin C is found in small amounts in milk and fresh meat, although it is quickly destroyed by heating. Primates, guinea pigs and bats all need this vitamin in their diet, and so they learned to eat fruit and vegetables as part of their diet.
A Quick History
Early in the 20th century, it was found that there were essential dietary ingredients in both the fatty and water-based components of milk. The former was called "Factor A", (vitamin A), the latter "Factor B" (vitamin B). It was soon realised that vitamin B was a mixture of chemical compounds known as amines, hence the term vitamin or "vital-amine". The naming of the vitamin B complex progressed sequentially, B1, B2, B3, B6, B12 etc., but there were gaps which reflected duplications or errors. The naming of other vitamins progressed alphabetically for a while, with vitamins C, D, E and K surviving scrutiny to the present day.
Fat Soluble or Water Soluble?
This is the key to their occurrence, metabolic function and toxicity. Vitamins A, D, E and K are fat soluble and found widely in dairy products and meat, with vitamin E found mainly in vegetable oils and eggs. Plants such as carrots and peppers contain the yellow/orange pigment beta-carotene, which the body converts to retinol, so an aversion to dairy produce need not compromise vitamin A intake. The functions of these vitamins deserve closer study:
- Vitamin A is needed to support normal vision, and maintain the lining surfaces (epithelia) of the gut and skin.
- We can store excess vitamin A in our fat cells, but above a certain level, it becomes toxic to the body. Consuming above 200mg per day will produce toxicity-related symptoms in adults.
- Treat all vitamin A supplements with caution, especially during pregnancy, when the intake of rich sources of the vitamin (such as liver and kidney ) should be restricted.
- Vitamin D is needed for the absorption of calcium via the gut wall, and is also toxic in concentrations above 20 micrograms per day. Check the units carefully on all supplements.
- Vitamin E is a powerful antioxidant - and it also helps in the formation of red blood cells.
- Vitamin K is needed for normal blood clotting and is produced by symbiotic bacteria living in our gut.
Water-soluble vitamins include all the vitamins in the B group, vitamin C, biotin, folate and pantothenic acid. These are found in a wide variety of plant and animal based foods, although vitamin B12 is not found in plants, and is a potential shortfall in the diet of strict vegetarians, unless supplemented foods are included.
- Water-soluble vitamins are more difficult for the body to store, although not impossible. Our liver can store vitamins from the B complex, vitamin K, folate and even some vitamin C!
- Nevertheless, water soluble vitamins are less toxic by virtue of their solubility in water, can be lost in the urine, and need to be replaced more regularly in the diet compared to fat-soluble vitamins.
- They cover a wide variety of functions.
The best source of all these vitamins will always be a balanced diet. Supplements are a useful stand-by when meals are badly planned or missing. Athletes and body builders may need extra supplements, but beware the marketing ploy which suggests that "more is better." Our bodies have been handling our vitamins requirements a lot longer than the editors of nutrition and food magazines!
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