Mothers who had low vitamin D levels while they were pregnant are more likely to have a child with a language impairment than moms who had higher levels of the vitamin, according to a new study from Australia.
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 published in the journal Pediatrics.
Dr. 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 behavioural and language development as well.
Twenty years ago, they measured the vitamin D levels of more than 700 women who were about halfway through their pregnancy.
Five and 10 years later, they tested the children of these moms to measure their behavioural 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 behavioural issues was the same for each group.
The low-vitamin D group had between 15 and 46 nanomoles per litre (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 per cent of moms in the lowest group had a child with a language issue at age 10, compared to roughly eight per cent 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," Dr. Whitehouse wrote in a e-mail.
"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.
Dr. 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.
Dr. 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.
The Institute of Medicine recommends that pregnant women get 600 international units (IUs) of vitamin D per day.