http://intl.ajcn.org/cgi/content/full/79/5/717

American Journal of Clinical Nutrition, Vol. 79, No. 5, 717-726, May 2004
© 2004 American Society for Clinical Nutrition
REVIEW ARTICLE
Assessment of dietary vitamin D requirements during pregnancy and
lactation1,2
Bruce W Hollis and Carol L Wagner

(the article is long and comprehensive, referencing over 100 other
studies; below some highlights)


...a 0.5-h exposure to the summer sun between 1000 and 1400 in a bathing
suit (3 times the minimal erythemal dose) will initiate the release of
50 000 IU (1.25 mg) vitamin D into the circulation within 24 h of
exposure in white persons (25). African Americans require up to 5 times
this solar exposure to achieve the same response (26, 27). In whites who
have a deep tan because of melanin deposition in the skin, the response
is 50% of that stated above, ie, only 20 000–30 000 IU (500–750 µg)
vitamin D will be liberated (28). Finally, if wearing clothing or total
body sunscreen, the cutaneous release of vitamin D is completely blunted
(24, 29-31). So, in light of the above facts, a DRI of 400 IU/d (10
µg/d) in adults seems woefully inadequate to maintain normal circulating
concentrations of vitamin D in adults with minimal solar exposure.
....
In the most recent study, by Datta et al (37), 160 pregnant minority
women in the United Kingdom were provided with 800–1600 IU (20–40 µg)
vitamin D/d for the duration of their pregnancy. Using modern assay
technology for the measurement of circulating 25(OH)D concentrations
(21), these investigators found a mean (± SD) increase in circulating
25(OH)D concentrations (ng/mL) of from 5.8 ± 0.9 at the beginning of
pregnancy to 11.2 ± 6.3 at term after vitamin D supplementation. A
normal serum circulating 25(OH)D concentration in the United States is
considered to be > 15 ng/mL (20). However, a circulating concentration
of 15 ng 25(OH)D/mL is marginal for nutritional vitamin D status (10).
In other words, mothers who were vitamin D deficient at the beginning of
their pregnancy were still deficient at the end of their pregnancy after
being supplemented with 800–1600 IU vitamin D/d throughout their pregnancy.
....
We are conducting an ongoing study that involves the supplementation of
lactating mothers with 2000 IU (50 µg; n = 9) or 4000 IU (100 µg; n = 9)
vitamin D/d for 3 mo. Our preliminary data show increased mean (± SD)
circulating 25(OH)D concentrations in the 2000-IU/d group (from 27.6 ±
9.8 to 36.1 ± 7.0 ng/mL) and in the 4000-IU/d group (from 32.6 ± 6.9 to
44.5 ± 11.4 ng/mL), all of which are within the normal reference range
(38). We note that the breastfeeding infants of these mothers have a
substantially improved nutritional vitamin D status because of the
transfer of vitamin D into the mother’s milk. Circulating 25(OH)D
concentrations in the infants of mothers receiving the 4000-IU/d dose
increased into the normal range after only 3 mo of breastfeeding (38).
...
Our group recently performed similar studies, supplementing lactating
women with 2000 or 4000 IU vitamin D/d for 3 mo (38). We found that
high-dose maternal vitamin D supplementation not only improves the
nutritional vitamin D status of breastfeeding infants but also elevates
the maternal concentrations into the mid-normal range. Thus, a dual
benefit is achieved from high-dose maternal supplementation. It is
noteworthy that in the Finnish study, the authors added a disclaimer, "A
sufficient supply of vitamin D to the breastfed infant is achieved only
by increasing the maternal supplementation up to 2000 IU/d. Such a dose
is far higher than the RDA [DRI] for lactating mothers [and therefore]
its safety over prolonged periods is not known and should be examined by
further study." This point of concern was valid when this study was
conducted in 1986 (92); however, on the basis of the current findings of
Vieth et al (2) and of Heaney et al (3)—which showed that vitamin D
intakes 10 000 IU/d (250 µg) are safe for prolonged periods (up to 5
mo)—we believe that it is time to reexamine the understated DRI of
vitamin D for lactating mothers. This work is now being conducted in our
clinics and laboratory.

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