Biotin intake

Biotin is widespread in foods, although its availability is affected somewhat by the presence of binding proteins. Biotin is required in only small amounts. Although US RDA values have not been established, the estimated safe and adequate intake of biotin is 30-100 g day -1 for adults. The Department of Health (1991) suggested that biotin intakes between 10 and 200 iig day-1 are safe and adequate. Biotin is reported to be non-toxic in amounts up to at least 10 mg day-1. 

Birds are especially sensitive to biotin deficiency, at least partly because their intestinal flora make little or no contribution to biotin intake. This is of considerable commercial importance with intensively reared poultry. In adult birds, biotin deficiency does not affect egg production, but does reduce the amount of biotin in the eggs, thus impairing embryonic development. In severe deficiency, the hatchability of the eggs can fall to near zero. 

It is apparent from the discussion in Section 11.3 that there is Utde information concerning human biotin requirements and no evidence on which to base recommendations. Average intakes of biotin range between 15 to 70 /rg per day. Such intakes are obviously adequate to prevent deficiency, and the safe and adequate range of biotin intakes is set at 10 to 200 /xg per day (Department of Health, 1991 Scientific Committee for Food, 1993). The U.S./Canadian adequate intake for adults is 30 /xgper day (Institute of Medicine, 1998). 

The Food and Nutrition Board of the US National Research Council has released adequate intakes for infants, adults and pregnant women (Mock 2004 National Research Council 1989 Yates et al. 1998). These recommendations (Table 43.1) refer to studies assuming that, with a daily dose of 60 pg of biotin, adults on parenteral nutrition declared they were symptom-free for six months and with diets supplying 28 2pg/day, no inadequate biotin status was observed. The dietary biotin intake in Western populations has been estimated to be 35-70 pg per day (143-287 nmoles per day). 

An intake of 50 mcg/1,000 kcal should provide adequate biotin intake for infants and older children. 

Biotin intake in average U.S. diet—Mixed American diets are thought to provide a biotin intake of 100 to 300 meg/day for adults. In western Europe, the dietary intake of biotin has been calculated to be between 50 and 100 meg/ day. 

Foods relatively rich in biotin are listed in Table 3. The average daily dietary biotin intake has been estimated to be approximately 35-70 pg. 

Because there is less information upon which to base dietary allowances for biotin and pantothenic acid, ranges of intake are provided, as in Table 8. 

Table 1. 1989 Estimated Safe and Adequate Daily Dietary Intake for Biotin...

RDA have been established for many essential nutrients however, present knowledge of human nutritional needs of pantothenic acid and biotin is incomplete. Therefore, to ensure adequate nutrient intake, obtain the recommended allowances from as varied a selection of foods as possible. Nutritionists suggest that dietary planning include regular intake of each of the four basic food groups ... 

Institute of Medicine. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin Bg, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington National Academy, 1998. 

Acquired biotin deficiency is extremely rare but may occur in special conditions such as long-term parenteral nutrition without biotin supplementation, short bowel syndrome and after excessive intake of raw egg white, which contains the potent bio-tin-binding protein avidin. The main symptoms are alopecia and skin abnormalities which resolve after administration of biotin [2, 30]. 

Fenech, M., Baghurst, P., Luderer, W., Turner, J., Record, S., Ceppi, M., and Bonassi, S. (2005). Low intake of calcium, folate, nicotinic acid, vitamin E, retinol, beta-carotene and high intake of pantothenic acid, biotin and riboflavin are significantly associated with increased genome instability—Results from a dietary intake and micronucleus index survey in South Australia. Carcinogenesis 26, 991-999. 

Deficiency can be due to two known genetic disorders of biotin metabolism or be induced by excess intake of avidin, which binds biotin and thus leads to poor absorption. Symptoms are alopecia, eczema around nose and mouth, conjunctivitis, hyperaesthesia, paraesthesia, depression, and muscle pain 29 The recommended daily allowance is 30 to 35 fig.112... 

Adequate Intake For some vitamins, notably biotin (Section 11.5) and pantothenic acid (Section 12.6), dietary deficiency is more-or-less unknown, and there are no data from which to estimate average requirements or derive reference intakes. In such cases, the observed range of intakes is obviously more than adequate to meet requirements, and the average intake is used to calculate an adequate intake figure. 

Biotin uptake into enterocytes is by a sodium-dependent carrier, which also transports pantothenic acid (Section 12.2) and lipoic acid, but is inhibited by biocytin and dethiobiotin. The carrier is found in both the small intestine and the colon, so both biotin and pantothenic acid synthesized by intestinal bacteria can be absorbed (Chatterjee etal., 1999 Ramaswamy, 1999 Said, 1999 Prasad and Ganapathy, 2000). Even at relatively high intakes (up to 80 /rmol), biotin is more-or-less completely absorbed (Zempleni and Mock, 1999b). 

The problem is a functional deficiency of biotin, due both to inability to release free biotin from dietary biocytin and also to failure of the normal recovery of free biotin by biotinidase action on the biocytin released by proteolysis of biotin-containing enzymes. Normal intakes of biotin are inadequate to meet the requirements of these patients the provision of pharmacological doses of free biotin provides an adequate amount to meet requirements without the need for reutUization. The delayed development of clinical and biocheimcal abnormalities is a result of the accumulation of biotin by the fetus, so that at birth the infant has adequate stores of the vitamin. 

More recently, similar signs of biotin deficiency have been observed in patients receiving total parenteral nutrition for prolonged periods, after major resection of the gut. The signs resolve after the provision of biotin, but again there have been no studies of the amounts of biotin required intakes have ranged between 60 to 200 /xg per day (Mock et al., 1985). 

The plasma concentration of the biotin does not provide a sensitive index of stams, at least partly because there is increased renal reabsorption of the vitamin as intake falls. Urinary excretion of biotin and its metabolites is more sensitive, but may be confounded by changes in biotin excretion caused by glucocorticoid hormones (McMahon, 2002). There are three sensitive markers of stams (Mock, 1999) ... 

Vitamin D is partly produced by the skin on exposure to sunlight vitamin K and biotin are produced in part by intestinal bacteria and vitamin B12 is especially well-stored. Hence, it is uncommon to have a deficiency of these vitamins on the basis of dietary intake alone. Infants, who have less bacterial intestinal flora and relatively little stores of vitamin K have a greater need than adults for vitamin K in the diet. 

National Academy of Sciences Food and Nutrition Board, Dietary reference intakes for thiamin, riboflavin, niacin, vitamin B6, folate, vitamin B12, pantothenic acid, biotin and choline. National Academy Press, Washington D.C., 1998, pp. 309 22. 

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