(Kalkwarf et al., 1997). Neither of the AHRQ analyses addressed calcium and BMD during lactation. Both RCTs and observational studies indicate that increased dietary calcium intake does not suppress maternal bone resorption during lactation (Cross et al., 1995; Fairweather-Tait et al., 1995; Prentice et al., 1995; Kalkwarf et al., 1997; Laskey et al., 1998; Polatti et al., 1999) nor does it alter the calcium content of human milk (Kalkwarf et al., 1997; Jarjou et al., 2006). Further, the calcium content of human milk does not predict maternal BMD decline, but breast milk volume does (Laskey et al., 1998), although milk calcium content is known to vary within and between feeds, complicating interpretation. During the post-lactation period (6 to 12 months), maternal bone mineral is deposited; in turn, maternal BMD is restored to pre-lactation levels without any consistent evidence of a need for higher calcium intake compared with non-pregnant women (Sowers, 1996; Kovacs and Kronenberg, 1997; Kalkwarf, 1999). Two RCTs found no effect of calcium supplementation post-weaning (Cross et al., 1995; Prentice et al., 1995), although one RCT found a slightly greater (1.5 percent) increase in BMD in calcium-supplemented women post-weaning (Kalkwarf et al., 1997). Adolescents, like adults, resorb bone during lactation and recover fully afterward, with no evidence that lactation impairs achievement of peak bone mass (Chantry et al., 2004). Maternal BMD is therefore informative for DRI development.
Calcium balance Although calcium balance is negative during lactation owing to the enhanced bone resorption discussed above, mothers are restored to a positive balance and net accretion of bone mineral immediately upon cessation of lactation, followed by BMD restoration. Notably, urinary calcium excretion decreases during lactation. Thus, during lactation, higher calcium intakes will be less well tolerated and may not be needed, because higher calcium intake does not suppress bone loss. Calcium balance in lactation can be informative for DRI development.
Overall, available evidence indicates that the maternal calcium requirement is not increased during lactation, and it may also not be increased during the post-weaning interval in which the skeleton recovers to its pre-pregnancy baseline BMC.
POTENTIAL INDICATORS FOR LACTATION: VITAMIN D As noted above, lactation is a period of transient bone loss, but it is discussed here in order to consider pregnancy and lactation contiguously and because BMD is restored in