A new study has found that iodine deficiency during pregnancy slows the mental development of the child.

Previous research has linked iodine deficiency with lack of mental growth. Severe iodine deficiency during pregnancy can lead to a condition called cretinism, where the child is unable to grow mentally and physically.

However, in the present study, researchers have found that even mild-to-moderate levels of iodine deficiency during pregnancy can affect the child's development. Iodine plays an important role in the production of hormones made by the thyroid gland. These hormones have a direct effect on brain development.

The study, conducted by researchers from Surrey and Bristol universities, included about 1,000 women and their children. The study team derived data from a long-term health study called Avon Longitudinal Study of Parents and Children.

Researchers assessed the levels of iodine in about 1,040 mothers and found that mothers who had low iodine levels during pregnancy had kids with lower IQ than their peers. The team found that the link between iodine deficiency and IQ remained the same even after they controlled for other factors such as education levels of the parents.

"Our results clearly show the importance of adequate iodine status during early pregnancy, and emphasise the risk that iodine deficiency can pose to the developing infant, even in a country classified as only mildly iodine deficient," said Margaret Rayman of the University of Surrey, in Guildford, U.K., lead author of the study, according to a news release.

The main source of iodine today is iodized table salt. Other sources of iodine include seafood, especially cod, sea bass, haddock and perch. Also, kelp, a type of seaweed, has large amounts of the nutrient.

The study is published in the journal The Lancet.