Pregnant women who skip out on foods that contain iodine, like milk and fish, may be lowering their baby's IQ and reading abilities.
A study published on May 22 in The Lancet showed that even women who had just a mild iodine deficiency were more likely to give birth to babies with lower verbal IQ scores, as well as lower reading abilities than women who got enough of the mineral.
"It's not a nutrient that many people would have heard of in terms of pregnancy, so this is the information we want to get out to raise the importance of iodine," study author Dr. Sarah Bath, a postdoctoral research fellow and registered dietitian, told the BBC.
Iodine is a mineral that is found naturally in the body. It is essential for cell metabolism, a process which converts food into energy. Iodine also facilitates thyroid function, which regulates the rate of metabolism and the production of thyroid hormones.
The Food and Nutrition Board at the U.S. Institute of Medicine recommends that women who are pregnant get 220 micrograms per day, and those producing breast milk may need 290 micrograms daily.
The main food source of iodine is table sat with iodine added. Seafood also has naturally high levels of iodine, specifically cod, sea bass, haddock and perch. Kelp also contains high levels of iodine, as do dairy products and plants grown in iodine rich soil.
For example, 6.8-ounce serving of cows milk has 50 to 80 micrograms of iodine, according to the British Dietetic Association. However, the same amount of organic cow's milk has only 30 to 65 micrograms of iodine, about 40 percent less. About 3.5 ounces of whitefish will give you 115 micrograms of iodine, the same amount of oily fish will provide 50 micrograms and shellfish will give you 90 micrograms. A 3.5-ounce portion of meat has only 10 micrograms of iodine.
The researchers looked at 1,040 pregnant women from southwest England. Iodine levels were measured from urine samples provided by women during their first trimester of pregnancy. Those who had 50 to 150 micrograms of iodine per liter of urine were said to have mild to moderate deficiencies and those with 50 micrograms or less had severe deficiencies. On average, the mothers had 90 micrograms of iodine per liter of urine, and about two-thirds of the mothers were determined to have an iodine deficiency. Iodine deficiency is thought to be a problem in developing countries, so the results were surprising.
"If iodine deficiency were rare I would not be so worried. But it is not rare. This may prevent a child reaching their full potential," Professor Jean Golding, founder of the Children of the 90s study where the data was pulled from, told the Independent.
Children of women with iodine deficiencies in early pregnancy had lower verbal IQ shores by the age of 8 when they were tested. Children had a 60 percent chance of being born in the group with the lowest quarter of IQ scores if their mother had iodine deficiencies. On average, children of mothers with low iodine levels scored six points lower on an IQ test compared to those of mothers who had enough iodine, even when other factors were ruled out. The children with iodine-deficient mothers also had lower reading accuracy and comprehension by the time they turned 9 years old.
There was no significant association between iodine levels and overall IQ, as well as number of words read per minute or overall reading score.
Bath noted that some studies have showed that children who get enough iodine during childhood may be able to improve their IQ scores, but she said pregnancy is a really important time because the brain is developing. The researchers also added that kelp or seaweed supplements added too much iodine which could cause thyroid problems.
"Our results clearly show the importance of adequate iodine status during early pregnancy, and emphasize the risk that iodine deficiency can pose to the developing infant, even in a country classified as only mildly iodine deficient," lead study author Margaret Rayman, a professor of nutritional medicine from the University of Surrey in the U.K, told Medical Daily.
Dr. Elizabeth N. Pearce, associate processor of medicine at Boston University, told Medscape the study is limited because it only used urine samples to determine iodine levels, which can fluctuate regularly depending on what the person ate recently. Still, Pierce, who wrote an accompanying editorial published in The Lancet, noted that the results could potentially be important and health officials should take note.
"I think it is both remarkable and concerning that cognitive effects of iodine deficiency were demonstrated even in children of only mildly iodine-deficient mothers," she said.