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:

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-