the post-lactation period. Potential indicators for vitamin D requirements during lactation are discussed below.

• Maternal BMD AHRQ-Ottawa found good evidence from one cohort study that there is no association between serum 25OHD level and maternal BMD during lactation. No studies have examined what level of maternal vitamin D intake is required for the maternal skeleton to recover lost mineral content after lactation, although one observational study (Ghannam et al., 1999) in Saudi women found no relationship between maternal serum 25OHD levels (including levels consistent with hypovitaminosis D) and lumbar or femoral neck BMD. There is no evidence that lactating adolescents require any more vitamin D or higher serum 25OHD levels than non-lactating adolescents. Thus, maternal BMD is of limited use in DRI development for lactation.

• Maternal and infant serum 25OHD levels Regarding lactation, maternal and infant serum 25OHD levels are of limited use given the present lack of consistent data. AHRQ-Tufts identified only one RCT, which it graded C (i.e., the report from Wagner et al., 2006), that found no effect of maternal supplemental vitamin D (6,400 IU) during lactation on infants’ weight or length. Eight other RCTs (Rothberg et al., 1982; Ala-Houhala, 1985; Ala-Houhala et al., 1988; Kalkwarf et al., 1996; Hollis and Wagner, 2004; Basile et al., 2006; Wagner et al., 2006; Saadi et al., 2007) suggest that maternal vitamin D supplementation increases maternal serum 25OHD levels but does not affect neonatal serum 25OHD levels unless the maternal intake of vitamin D is extremely high, in the range of 4,000 to 6,400 IU/day (Hollis and Wagner, 2004; Wagner et al., 2006). With respect to observational studies, maternal serum 25OHD levels are not affected by lactation (Kent et al., 1990; Sowers et al., 1998), although one study found an increase post-weaning (Cross et al., 1997). Observational studies (Cancela et al., 1986; Okonofua et al., 1987; Takeuchi et al., 1989; Kent et al., 1990; Alfaham et al. 1995; Sowers et al., 1998) also show little impact of maternal serum 25OHD levels. Thus, maternal and fetal serum 25OHD concentrations have limited utility for DRI development.

Summary of evidence for bone maintenance During bone maintenance, calcium intakes that maintain a neutral calcium balance have been recently elucidated in an important 2007 study (Hunt and Johnson, 2007) and are informative for the development of an EAR as well as an RDA. The relationship of calcium intake to BMD is more difficult to discern given the limited, and often contradictory observational data and relatively few and