status. The average daily amount of folate secreted in human milk is estimated to be 85 µg/L, as described in the previous section “Infants Ages 0 through 12 Months” (see “Human Milk”). The dietary intake needed to provide this amount must account for the estimated 50 percent bioavailability of food folate (see “Bioavailability”).
There are no metabolic studies in which lactating women consumed controlled amounts of dietary folate. It is unclear whether the reduction in maternal folate concentration observed in lactating women (Keizer et al., 1995; Qvist et al., 1986; Smith et al., 1983) is related to the discontinuation of use of prenatal folate supplements, loss of maternal body folate stores, or other factors. For example, in a recent study of lactating adolescents (Keizer et al., 1995), both breastfeeding mothers and mothers of formula-fed infants showed a decline in erythrocyte folate between 4 and 12 weeks postpartum, suggesting that the postpartum decline in folate status may not be related to lactation. The decrease was prevented by supplemental folate (300 µg/day).
In a recent study in which folate status was compared in supplemented and nonsupplemented lactating women (Mackey et al., 1997), dietary folate intake was estimated to be 400 µg/day. In the unsupplemented lactating women, plasma homocysteine concentrations increased significantly but remained well within the normal range (6 to 7 µmol/L); this increase, therefore, does not appear to be of nutritional significance.
The calculation used to obtain the extra amount of folate needed to cover lactation is
0.78 L (milk volume) × 85 µg/L (folate concentration) × 2 (bioavailability correction factor) =133 µg/day.
When this quantity is added to the EAR for the nonlactating nonpregnant woman (320 µg/day), the result is rounded down, giving an EAR of 450 µg/day of DFEs. Women who are only partially breast-feeding would need less.