BIOTIN

Function and essentiality Biotin was originally discovered as part of a complex which promoted the growth of yeast. It was also found to be the protective or curative factor in "egg white injury" which can be caused in man and experimental animals by feeding large amounts of raw egg white: the glycoprotein avidin in egg white binds biotin with a remarkably high affinity. Metabolically, biotin is of central importance in lipogenesis, gluconeogenesis and the catabolism of branched chain amino acids. Apart from patients maintained on total parenteral nutrition for long periods, deficiency is not known in man except in people who consumed large amounts of uncooked eggs and thus of avidin. They developed a fine scaly dermatitis and hair loss (alopecia). Histology of the skin showed an absence of sebaceous glands and atrophy of the hair follicles. In experimental studies of biotin depletion, diets providing up to 30 per cent of energy intake from raw egg white have been used. The subjects developed glossitis, anorexia, nausea, hallucinations, depression and somnolence, as well as a fine scaly desquamating dermatitis. Urinary excretion of biotin fell to about 10 per cent of that in subjects eating a normal diet. Injection of biotin reversed all the clinical signs (1).


Sources The vitamin is widely distributed in many foods, and is also synthesised by intestinal flora. Studies in vivo show that there is significant absorption of biotin from the proximal and mid-transverse colon, suggesting that biotin from intestinal bacteria can be absorbed (2). The extent to which it is available is, however, not known, for the faecal excretion of biotin is 3-6 times greater than the intake.


Requirements The signs of biotin deficiency that have been observed in patients receiving total parenteral nutrition for prolonged periods after major resection of the gut have resolved following the provision of 60-200 µg biotin, but there have been no studies of the actual amounts of biotin needed (3). The average intake by British men is 39 µg/d (range 15-70 µg) and by women is 26 µg/d (range 10-58 µg) (4). These amounts prevent deficiency, and the average requirement must lie below these values. Although the Panel could set no DRVs on such limited evidence, they agreed that biotin intakes between 10 and 200 µg/d were both safe and adequate.


References

1 Sydenstricker V P, Singal S A, Briggs A P, DeVaughn N M, Isbell H. Observations on the 'Egg White Injury' in man and its cure with a biotin concentrate. J Am Med Assoc 1942; 118: 1199-1120.

2 Bowman B B, Rosenberg I H. Biotin absorption by distal rat small intestine. J Nutr 1987; 117: 2121-2126.

3 Mock D M, Baswell D L, Baker H, Holman R T, Sweetman L. Biotin deficiency complicating parenteral alimentation: diagnosis, metabolic repercussions and treatment. J Pediatr 1985; 106: 762-769.

4 Gregory J, Foster K, Tyler H, Wiseman M. The Dietary and Nutritional Survey of British Adults. London: HMSO, 1990.