timing of calcium supplement intake would still be relevant to this group and are discussed in Chapter 8.
Hypercalciuria is often present during normal pregnancy as a consequence of the doubling of intestinal calcium absorption that occurs, and pregnancy itself increases the risk of kidney stones. Consequently, excess intakes of calcium during pregnancy will aggravate hypercalciuria and possibly increase the risk of kidney stones. During lactation, the serum calcium (both ionized and albumin-corrected total calcium) level rises and usually remains within the normal range (although hypercalcemia can occur during normal lactation), and urinary excretion of calcium is reduced to the low-normal range or below. Consequently, higher intakes of calcium during lactation could potentially increase the risk of hypercalcemia. However, there is no evidence to suggest that the risk manifests itself at intakes lower than the UL for non-pregnant or non-lactating women, although it is acknowledged that relevant studies have not been rigorously carried out for pregnancy and lactation. Given that available evidence suggests that requirements for calcium among pregnant and lactating females are similar to those of non-pregnant and non-lactating females, and lacking data to suggest a basis for a different UL, the ULs for calcium for pregnancy and lactation have been kept the same as those for their non-pregnant and non-lactating counterparts.
Few studies have been designed to specifically evaluate the safety of vitamin D intake, and there is not general agreement about the intake levels at which vitamin D may cause harm. A recent National Institutes of Health conference highlighted the lack of knowledge about mechanisms of action and toxic forms of the vitamin as well as the many limitations in the available evidence. Conference participants noted that available randomized controlled trials designed to illuminate health benefits likely