WebMD Medical News
Laura J. Martin, MD
May 4, 2010 -- Women who take high doses of vitamin D during pregnancy have
a greatly reduced risk of complications, including gestational diabetes,
preterm birth, and infection, new research suggests.
Based on the findings, study researchers are recommending that pregnant
women take 4,000 international units (IU) of vitamin D every day -- at least 10
times the amount recommended by various health groups.
Women in the study who took 4,000 IU of the vitamin daily in their second
and third trimesters showed no evidence of harm, but they had half the rate of
pregnancy-related complications as women who took 400 IU of vitamin D every
day, says neonatologist and study co-researcher Carol L. Wagner, MD, of the
Medical University of South Carolina.
Wagner acknowledges the recommendation may be controversial because very
high doses of vitamin D have long been believed to cause birth defects.
"Any doctor who hasn't followed the literature may be wary of telling their
patients to take 4,000 IU of vitamin D," she says. "But there is no evidence
that vitamin D supplementation is toxic, even at levels above 10,000 IU."
Most prenatal vitamins have around 400 IU of vitamin D, and most health
groups recommend taking no more than 2,000 IU of the vitamin in supplement form
daily. Wagner says it took months to get permission to do a study in which
pregnant women were given doses of the vitamin that were twice as high as
The study included about 500 women in Charleston, S.C., who were in their
third or fourth months of pregnancy. The women took 400 IU, 2,000 IU, or 4,000
IU of vitamin D daily until they delivered.
Not surprisingly, women who took the highest doses of vitamin D were the
least likely to have deficient or insufficient blood levels of the vitamin, as
were their babies.
These women also had the lowest rate of pregnancy-related complications.
Compared to women who took 400 IU of vitamin D daily, those who took 4,000
IU were half as likely to develop gestational diabetes, pregnancy-related high
blood pressure, or preeclampsia, Wagner says. They were also less likely to
give birth prematurely.
The research was presented over the weekend at the annual meeting of the
Pediatric Academic Societies in Vancouver, British Columbia.
Infants with very low vitamin D levels are at increased risk for soft bones,
or rickets -- a condition that is now rare in the U.S.
But over the last decade, more and more studies suggest that vitamin D also
protects against immune system disorders and other diseases, Wagner says.
Fortified milk and fatty fish are common food sources of vitamin D, but most
people get only a small fraction of the vitamin D they need through food,
Wagner says. Instead, the body makes vitamin D from sunlight.
But even in sunny climates like Charleston, few people are now getting
adequate levels of vitamin D from sun exposure.
At the start of the study, deficient or insufficient levels of vitamin D
were seen in 94% of the African-American women, 66% of Hispanic women, and 50%
of white women who participated.
University of Rochester professor of pediatrics Ruth Lawrence, MD, has been
recording vitamin D levels in new mothers and their infants for three years.
She did not take part in the new study.
Lawrence, who chairs the breastfeeding committee of the American Academy of
Pediatrics, says exclusively breastfed babies whose mothers have low vitamin D
levels and who don't take vitamin supplements are most likely to be
"It is clear that both for mothers and their babies, vitamin D levels are
low," she tells WebMD. "This is true in northern areas like Rochester and in
sunny climates like Charleston."
Lawrence sees no problem with the recommendation that women take 4,000 IU of
vitamin D daily during pregnancy, although she says the impact of high doses of
vitamin D on pregnancy-related complications remains to be proven.
"Four thousand IU may sound outrageous to some, but I believe it is really
not unreasonable," she says.
"We have been searching for the causes of preeclampsia and premature birth
for many years. It is reassuring that the risk of these complications are lower
for women taking extra vitamin D, but it is premature to say it is the
The independent health policy group the Institute of Medicine recommends 200
IU to 400 IU of vitamin D a day for everyone, including pregnant women, but
this recommendation is under review. Revised guidelines are expected late this
SOURCES:Pediatric Academic Societies annual meeting, Vancouver, British Columbia,
May 1-4, 2010.Carol L. Wagner, MD, neonatologist and pediatric researcher, Medical
University of South Carolina, Charleston.Ruth Lawrence, MD, professor of pediatrics, University of Rochester School
of Medicine, New York.News release, American Academy of Pediatrics.
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