Biotin is involved in a number of carboxylase reactions. It occurs in many foodstuffs and the dietary requirement is small. Deficiency is extremely rare and is confined to a few people who consume raw eggs, which contain an antagonist (avidin) to biotin. It causes a dermatitis that responds to biotin replacements.
Pantothenic acid is widely distributed in all foods and deficiency in humans has not been described.
Ascorbic acid is a simple sugar and a powerful reducing agent, its main role being to control the redox potential within cells. It is involved in the hydroxylation of proline to hydroxyproline, which is necessary for the formation of collagen. The failure of this biochemical pathway in vitamin C deficiency accounts for virtually all of the clinical effects found.
Humans, along with a few other animals (e.g. primates and the guinea-pig) are unusual in not being able to synthesize ascorbic acid from glucose. Vitamin C is present in all fresh fruit and vegetables.
Unfortunately, ascorbic acid is easily leached out of vegetables when they are placed in water and it is also oxidized during cooking. Potatoes are a good source as many people eat a lot, but vitamin C is lost during storage. Vitamin C deficiency is mainly seen in infants fed boiled milk and elderly and single people who cannot be bothered to eat vegetables. In the UK it is also seen in Asians eating only rice and chapa tis, and in food faddists.
In adults the early symptoms may be non-specific, with wealcness and muscle pain. Other features are shown in Table 3.8. In infantile scurvy there are irritability, painful legs, anaemia and characteristic subperiosteal haem orrhages, particularly into the ends of long bones.
The anaemia is usually hypochromic but occasionally a normochromic or megaloblastic anaemia is seen. The type of anaemia depends on whether iron deficiency (due to decreased absorption and loss due to haemorrhage) or folate deficiency (folate is largely found in green vegetables) is present.
Plasma ascorbic acid is very low in obvious deficiency and a vitamin C level of less than 15!Lg per 108 cells in the leucocyte-platelet layer (buffy coat) of centrifuged blood indicates deficiency.
Ascorbic acid should be given in doses of up to 1 g a day initially and patients should be encouraged to eat fresh fruit and vegetables.
Orange juice should be given to bottle-fed infants. The intake of breast-fed infants depends on the mother’s diet. In the elderly, eating adequate fruit and vegetables is the best way to avoid scurvy. Careful surveillance of the elderly, particularly those who live alone, is necessary. Ascorbic acid supplements should only be necessary occasionally. Ascorbic acid in high dosage has been suggested as a treatment of cancer and the common cold. There is some scientific support for its value; however, clinical trials in the common cold have shown that it is of no help.
VITAMIN 812 AND FOLATE
These are dealt