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This approach of normalization to baseline is a complicated way to determine baseline vitamin intake and does not directly address the requirement for the vitamin.

In the discussion that follows, data are reanalyzed, particularly from some recent studies, to arrive at an Estimated Average Requirement (EAR) for some adult age groups. Various indicators of B6 status are used, but when possible, a plasma pyridoxal phosphate (PLP) value of at least 20 nmol/L is used as the major indicator of adequacy.

Most controlled studies on B6 requirements have used a liquid formula diet (which contains some food-bound B6) supplemented with synthetic PN. Because PN is 95 percent bioavailable whereas food B6 is only about 75 percent bioavailable, synthetic B6 is 95/75 (i.e., 1.27) times more available. Thus, dietary B6 equivalents are calculated as follows to determine the EAR:

mg of dietary B6 equivalents provided = mg of food B6 + (1.27 × mg of synthetic B6).

Infants Ages 0 through 12 Months

Method Used to Set the Adequate Intake

An Adequate Intake (AI) is used as the goal for intake by infants. Limited data are available on B6 requirements of the infant, but an AI can be set based on human milk B6 content, which varies with maternal B6 intake. West and Kirksey (1976) reported an average B6 content of 0.13 mg/L of human milk at maternal B6 intakes of less than 2.5 mg and 0.24 mg/L at intakes of 2.5 to 5 mg. However, milk B6 content was quite variable between subjects at similar B6 intakes. Borschel and colleagues (1986) reported that the milk of mothers receiving 2.5 mg/day of PN as a supplement contained 0.15 to 0.21 mg/L of B6.

Ages 0 through 6 Months. The AI reflects the observed mean B6 intake of infants consuming human milk. Thus, the B6 AI for young infants is based on mean intake data from infants fed human milk as the principal food during their first 6 months and uses the B6 concentration of milk produced by well-nourished mothers. There are no reports of full-term infants exclusively and freely fed human milk from U.S. or Canadian mothers who manifested any signs of B6 deficiency. The mean concentration of B6 in human milk of well-

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