While the results do not prove that low vitamin D is to blame for later problems, "they point to a very plausible association that warrants more attention," said Lisa Bodnar, a professor at the University of Pittsburgh, who was not involved in this study.

Vitamin D is important for fetal development, but "the effects of lower maternal vitamin D levels on the developing offspring is not fully understood," said Andrew Whitehouse, the lead author of the study.

Whitehouse said earlier studies have shown some links between low vitamin D during pregnancy and problems in children such as weaker bones, asthma and poor growth.

He and his colleagues, based at the University of Western Australia, sought to determine whether vitamin D levels in the moms might have anything to do with kids' later behavioral and language development as well.

Twenty years ago, they measured the vitamin D levels of more than 700 women who were about half-way through their pregnancy.

Five and 10 years later, they tested the children of these moms to measure their behavioral and emotional development and language skills.

The researchers split the moms into four groups -- from lowest to highest vitamin D levels -- and they found that the risk of having a kid with emotional or behavioral issues was the same for each group.

The low-vitamin D group had between 15 and 46 nanomoles per liter (nmol/L) in their blood, while the high-vitamin D group had 72 to 154 nmol/L. Levels below 30 nmol/L are considered deficient.

When the researchers looked at language skills, the team found that mothers in the lowest category were more likely to have a child with a language impairment than mothers in the highest vitamin D category.

The language impairments were determined from scores on a vocabulary test.

For instance, about 18 percent of moms in the lowest group had a child with a language issue at age 10, compared to roughly eight percent of the moms in the highest group.

"The logical thought is that maternal Vitamin D insufficiency during pregnancy is affecting the normal course of brain development," Whitehouse told Reuters Health by email.

"If vitamin D insufficiency during prenatal life is a cause of childhood language difficulties -- and this still needs to be determined conclusively -- then Vitamin D supplementation of pregnant women may be an important next step," he said.

NO CAUSE-EFFECT SHOWN

Whitehouse made clear that his study, published in Pediatrics, does not show a cause-and-effect relationship between vitamin D and language problems.

Bodnar said one factor that will be important to tease out is whether obesity might be involved.

"We know that obesity before pregnancy is associated with poor vitamin D status in pregnancy, and we know that obese moms are more likely to have children with developmental delays and cognitive impairments," she said.

Bodnar said it will be important for future studies to determine if vitamin D is to blame for the language impairments, because it's a simple problem to fix with supplements. Sunlight is also a primary source of vitamin D.

Whitehouse said he'd like to see his study replicated.

The American College of Obstetricians and Gynecologists does not currently recommend that pregnant women get screened for or take supplements for vitamin D, unless told to do so by their medical provider (see Reuters Health report of June 20, 2011).

The Institute of Medicine recommends that pregnant women get 600 international units (IUs) of vitamin D per day.

SOURCE: bit.ly/xyuOsR Pediatrics, online February 13, 2012.

• A Permanent Economic Emergency