The total body pool of vitamin B12 is of the order of 1.8 f mol (2.5 mg), with a minimum desirable body pool of about 0.3 f mol (1 mg).
Table 10.3 Reference Intakes of Folate (^g/day)
U.K. EU U.S./Canada 1991 1993 1998
7-8y 150 150
65 80 150 200 200
80 80 160 200 300
300 300 400
300 400 400
9-10 y 150 150
11-13y 200 180
Pregnant 300 400
Lactating 260 350
300 300 400 600 500
EU, European Union; FAO, Food and Agriculture Organization; WHO, World Health Organization. Sources: Department of Health, 1991; Scientific Committee for Food, 1993; Institute of Medicine 1998; FAO/WHO, 2001.
The daily loss is about 0.1% of the body pool in subjects with normal intrinsic factor secretion and enterohepatic circulation of the vitamin (Section 10.7.2). On this basis, the requirement is 0.3 to 1.8 nmol (1 to 2.5 ¿g) per day (Herbert, 1987b). This is probably a considerable overestimate of requirements, because parenteral administration of less than 0.3 nmol per day is adequate to maintain normal hematology in patients with pernicious anemia, in whom the enterohepatic recycling of the vitamin is grossly impaired.
Requirements are probably between 0.1 to 1 [g per day; as shown in Table 10.4, reference intakes range between 1 to 2.4 [g per day, which is considerably lower than the average intake of 5 [g per day by nonvegetarians in most countries.
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