Vitamin Bi2 Requirements

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

FAO 2001

7-8y 150 150

65 80 150 200 200

80 80 160 200 300

Males

300 300 400

300 400 400

Females

9-10 y 150 150

11-13y 200 180

Pregnant 300 400

Lactating 260 350

300 300 400 600 500

300 400 400 600 500

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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