Female physiology adapts to meet the demands for calcium
delivery imposed by pregnancy and lactation, but without requiring
vitamin D or calcitriol. Animal and human data have shown that
the fetus should have normal serum chemistries, calciotropic hormones,
and skeletal mineral content at term despite severe vitamin
D deficiency, VDDR-I, or VDDR-II in the mother or fetus. It is the
neonate and especially the infant that are at risk for postnatal
hypocalcemia and rickets if vitamin D deficiency is present.
Breastfed babies are at higher risk for these complications because
breast milk normally contains very little vitamin D or 25(OH)D.
Overall it appears that pregnant and lactating women do not
require a higher intake of vitamin D or 25(OH)D compared with
non-pregnant women, and that intake should also provide most
term infants with a 25(OH)D level of 50 nmol/L. Prescribing
higher vitamin D intakes may make the physician and patient more
comfortable, but it should be recognized that typical higher intakes
will do nothing to the lactating mother or her breast milk calcium.
Intakes of w6400 IU per day may be needed to insure sufficient
vitamin D and 25(OH)D in the milk. These data should also reassure
us that if a baby is born vitamin D deficient it is not too late to act
because the fetus will likely be normal. All neonates require
attention to insure that vitamin D intake remains adequate.
The purported non-skeletal benefits of vitamin D are supported
by inconsistent data from animal models and associational studies.
A cause-and-effect relationship has not been demonstrated
between vitamin D intake or 25(OH)D and non-skeletal outcomes
of interest. Available randomized clinical trials have not shown any
obstetrical or neonatal benefit apart from raising maternal, fetal,
and neonatal 25(OH)D levels. Consequently, no specific vitamin D
intake can be recommended to prevent any of the possible nonskeletal
benefits of calcitriol. We must await the results of clinical
trials that are examining outcomes such as prevention of type 1
diabetes in infants.