Another study suggests higher levels of vitamin D during pregnancy may play an important role in a baby's future health. In the latest study, Vitamin D deficiency during pregnancy has been linked to poorer mental and motor skills in babies.
Researchers in Spain measured the level of vitamin D in the blood of almost 2,000 women in their first or second trimester of pregnancy and evaluated the mental and motor abilities of their babies at about 14 months of age. The investigators found that children of vitamin D deficient mothers scored lower than those whose mothers had adequate levels of the vitamin.
"These differences in the mental and psychomotor development scores do not likely make any difference at the individual level, but might have an important impact at the population level," said study lead author Dr. Eva Morales, a medical epidemiologist in the Center for Research in Environmental Epidemiology in Barcelona.
One concern is that lower scores in motor and mental tests could lead to lower IQs.
Previous studies have linked a deficiency in vitamin D during pregnancy to babies born with a greater risk for developing language problems, higher body fat, bone weakness, lung infections and schizophrenia.
Vitamin D deficiency in moms-to-be has also been associated with a higher risk for developing preeclampsia. Preeclampsia is when a pregnant woman develops high blood pressure and protein in the urine after the 20th week of pregnancy. It is rarely fatal, but can lead to premature births.
How much vitamin D should a pregnant woman be getting? There's not a clear-cut answer.
The Institute of Medicine, an independent U.S. group that advises the public, recommends pregnant women get 600 international units (IU) a day of vitamin D and no more than 4,000 IU/day. However, the Endocrine Society says that 600 units does not prevent deficiency and that at least 1,500 to 2,000 units a day may be required.
Bruce Hollis, director of pediatric nutritional sciences at the Medical University of South Carolina in Charleston, said the recommended 600 units per day is probably sufficient to promote good skeletal health in fetuses, but it "basically does nothing" to prevent other diseases.
Hollis recommends that women who are pregnant or want to become pregnant get 4,000 units a day of vitamin D.
In the current study, Morales and her colleagues measured vitamin D levels in 1,820 pregnant women living in four areas of Spain. Most were in their second trimester.
The researchers found that 20 percent of the women were vitamin D-deficient and another 32 percent had insufficient levels of the vitamin.
Morales and her colleagues found that the babies of mothers whose prenatal vitamin D level was deficient scored on average 2.6 points lower on a mental test and 2.3 points lower on a psychomotor test at about 14 months of age than babies of women whose prenatal vitamin D level was adequate.
Differences of between four and five points in these types of neuropsychological tests could reduce the number of children with above-average intelligence (IQ scores above 110 points) by over 50 percent, Morales noted.
The authors took into consideration other factors that could influence babies' mental and motor development, including birth weight, maternal age, social class and mother's education level, and whether or not the mother drank alcohol or smoked during pregnancy.
The study found a link between vitamin D deficiency during pregnancy and babies' brain development, but it did not prove the existence of a cause-and-effect relationship.
Vitamin D may have additional benefits for mothers-to-be. Other research conducted by Hollis and his team found that pregnant women taking vitamin D could lower their risk of pregnancy-related diabetes and high blood pressure.
Early studies suggesting that high levels of vitamin D could lead to birth defects were bogus, Hollis said.
Women can receive up to 50,000 units a day before worrying about having too much vitamin D, Hollis said. Excessive vitamin D can lead to spikes in blood levels of calcium, which can, in turn, lead to kidney and nerve damage and abnormal heart rhythm.
Scientists are in agreement that vitamin D is important during pregnancy for the mother as well as the baby, but since there is still some uncertainty about the correct dosage, discuss what vitamin D level is right for you with your obstetrician.
The study was published online in September and will be available in the October issue of the journal Pediatrics.