Consequently, an extra 0.5 mg/day of B₆ can be reasonably justified to meet the need in the third trimester.

Although 0.5 mg/day of B₆ may overestimate the additional need in early gestation, it was considered judicious to err on the side of ensuring sufficiency and add 0.5 mg/day to the EAR for nonpregnant women throughout pregnancy. Because of the approximation involved, no additional adjustment for adolescence is included.

The RDA for B₆ is set by assuming a coefficient of variation (CV) of 10 percent (see Chapter 1) because information is not available on the standard deviation of the requirement for B₆; the RDA is defined as equal to the EAR plus twice the CV to cover the needs of 97 to 98 percent of the individuals in the group (therefore, for B₆ the RDA is 120 percent of the EAR).

As described above, the B₆ concentration in human milk varies depending on the mother’s B₆ intake, and some women consuming less than 2.5 mg/day of B₆ produce milk with a B₆ content that is not much higher than that associated with consuming formula that resulted in convulsions in infants because of low levels of B₆. There is some variation in reported human milk B₆ content, which may be due to methodological differences. Between individuals there are variations in milk B₆ content at similar B₆ intakes. Existing data previously described suggest that the amount of B₆ required to increase the milk B₆ content by a small increment is much higher than that increment and that the additional requirement for lactation is considerably in excess of that suggested by the amount secreted via lactation (Borschel et al., 1986; West and Kirksey, 1976).