Pregnancy iodine pills 'good for babies and economy'
Recommending iodine supplements to all pregnant women could save the NHS money, say researchers.
A study in The Lancet concluded that if all pregnant women took a daily dose, it could boost children's IQ scores, causing health improvements.
Iodine is important for healthy brain development and there is some evidence that the UK population may not be getting enough.
But Public Health England (PHE) said a varied diet should offer enough iodine.
"The longstanding government advice is that everyone including pregnant women should be able to get all the iodine they need from a varied and balanced diet," said Dr Louis Levy, head of nutrition science, diet and obesity, at PHE.
Severe iodine deficiency has long been known to cause impaired neurodevelopment in unborn children.
But the picture is less clear in countries such as the UK where iodine intake may only be slightly below recommended levels.
The main source in the UK diet is milk but it can also be found in other types of dairy food, fish and - in smaller amounts - in some foods made from plants, such as cereals.
A previous UK study of around 1,000 pregnant women, published in 2013, found that around two-thirds could be classed as mildly to moderately deficient in iodine.
Lower levels of iodine during pregnancy were subsequently linked with slightly poorer IQ and reading scores when the children were eight years old.
Those 2013 findings sparked the latest study in which researchers calculated the potential impact of all women taking iodine supplements before conception, during pregnancy, and while they were breastfeeding.
They based the study on the assumption that around 67% of women do not get enough iodine from their diet, which is used by the body to make thyroid hormones.
Their estimates suggest that universal iodine supplements in pregnancy could boost children's IQ scores by an average of 1.22 points.
They then took evidence from other studies that had looked at economic benefits linked to IQ score.
Putting figures on the healthcare costs associated with different IQs - which had shown a higher IQ is associated with better health - into their model showed an average saving to the NHS of £199 per pregnant woman.
They also calculated, using previous research, that on average, the financial benefit for every pregnant woman taking the supplement would amount to £4,476 in higher earnings and lower education costs for her child.
Large study needed?
The latest study's author, Professor Kate Jolly from the University of Birmingham, said that ideally women who are deficient in iodine should be targeted.
But there was no easy way of knowing who they are.
She added that the UK was behind other countries, such as Australia, which already recommend supplements in pregnancy, and a change in guidance was warranted.
"The next step is we need a large scale look at the iodine status of pregnant women," she said.
No study has looked directly at the impact of giving iodine supplementation in populations that are only mildly to moderately deficient.
And because of ethical and cost concerns this is unlikely to happen, the researchers pointed out.
Last year the government's Scientific Advisory Committee on Nutrition called for more research into iodine levels in certain groups including "girls of reproductive age, pregnant and lactating women".
UK guidelines recommend that adults need around 0.14mg of iodine a day, while the World Health Organization advises that pregnant women should have 0.25mg a day.
Dr Sarah Bath, spokesperson for the British Dietetic Association, said it was important to stress that kelp and seaweed supplements should not be used as a source of iodine, especially by pregnant women, as they can in fact contain harmful amounts.
And she pointed out that some pregnancy supplements already contain iodine.
"Milk, dairy products and fish are good sources of iodine and eating a balanced diet that contains iodine sources will help to reduce the risk of iodine deficiency," she said.