Discovery of iodine deficiency among pregnant women presented in Doctoral Thesis of the Year
Pregnant women in Sweden have mild iodine deficiency, and breastfeeding women may have it as well. This has been shown by Sofia Manousou in her thesis, which has now been awarded Doctoral Thesis of the Year 2021 by the Institute of Medicine.
Iodine is a vital substance required to produce thyroid hormones that are important for metabolism. Pregnant women and nursing mothers have a 50% greater need for iodine and thus increased risk of iodine deficiency. The iodine status of pregnant women in Sweden has long been unclear because no national survey has been conducted – until 2019.
That is when Sofia Manousou and her colleagues showed in a national study of 743 pregnant women that many pregnant women had mild iodine deficiency and were on average beneath the WHO’s limit value for iodine during pregnancy. They also showed that a daily iodine supplement of 150 micrograms during pregnancy had a positive impact on the mother’s iodine status and thyroid metabolism.
“Because we could not show severe iodine deficiency, the study has not led to changed recommendations, but the Swedish National Food Agency has classified iodine as a critical nutrient and is awaiting more evidence on the matter of whether mild iodine deficiency impacts the foetus,” says Sofia Manousou.
Investigating the impact on children
More knowledge is on the way: the national SWIDDICH study is currently in progress. The study will follow over 1,200 pregnant women and cognitive development in the children that are born until age seven.
“We know that severe iodine deficiency during pregnancy can have serious consequences for the child, such as inhibited growth, developmental abnormalities and cognitive and motor difficulties. But we don’t know whether milder forms of iodine deficiency during pregnancy impact the child, or whether iodine supplements for pregnant women with mild iodine deficiency may have a positive impact on the child’s development. We’re not expecting particularly discernible effects for the individual mother and child; in that case; we’ll mainly see a benefit at the population level,” she says.
The study is led by Helena Filipsson Nyström, senior physician and associate professor at the Institute of Medicine and Sofia Manousou’s principal supervisor.
Changed diets are challenging
Sofia Manousou’s thesis also studied iodine deficiency in breastfeeding women. Eighty-four women in Gothenburg were monitored from late pregnancy until one year after delivery. Many of these women also had mild iodine deficiency. The results will be followed up with a new study to investigate whether iodine supplements while breastfeeding may improve iodine status in both the mother and child.
Sofia Manousou also notes that iodine supplements are not currently recommended for pregnant and breastfeeding women. Too much iodine is also harmful and getting the right dose may be difficult.
“It is important to use iodised salt, but at this point there is no reason to take iodine supplements unless you’re vegan,” says Sofia Manousou.
Changed dietary habits may be one of the reasons for increased incidence of iodine deficiency, not just among pregnant and breastfeeding women, but also in the population in general. Non-iodised salts, such as herb salt and flake salt, have increased in popularity, while the battle against high blood pressure has led many people to reduce their salt intake.
“We also eat fully and partially manufactured foods more often, which usually contain non-iodised salts because they’re cheaper for the food industry and can be used in large-scale production,” says Sofia Manousou.
Bariatric surgery not a risk factor
We do not know how iodine is absorbed by the body. In her fourth project, Sofia Manousou had the opportunity to study iodine status in yet another group: people who had undergone bariatric surgery. Three hundred seventy-six patients were followed up before undergoing gastric bypass or banded gastroplasty, and again two and ten years after the surgery.
Their iodine levels declined during that period, but because the patients had iodine intake at the upper level initially, they were still within the normal range relative to the rest of the population.
“The group of patients undergoing bariatric surgery is becoming bigger and bigger, and I thought it was important to investigate whether they need iodine supplements after surgery. Our conclusion is that bariatric surgery does not seem to result in iodine deficiency,” she says.
Sofia Manousou is a researcher at the Institute of Medicine and senior physician in diabetes and endocrinology, active at the medical clinic at Frölunda Specialist Hospital. She was awarded the prize for her dissertation Iodine intake and uptake in populations at risk for iodine deficiency.
The prize has been awarded since 2009 and is funded through donations from Dr. Amt Vestby’s Research Foundation. One prize-winner is selected from each institute, along with an overall winner for Sahlgrenska Academy.
TEXT: KARIN ALLANDER, PHOTO: PRIVATE
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- Occurs naturally in bedrock but the amount varies. Many areas in Sweden have low incidence.
- The nutrient is found in dairy products, fish, seafood and iodised salt.
- Too much and too little intake of iodine are both harmful.
- Pregnant and breastfeeding women as well as vegans are known risk groups for iodine deficiency.
- Iodine deficiency may lead to hyper- and hypothyroidism and to goitre (enlarged thyroid), a disease that used to be common in Sweden.
- Incidence of goitre has significantly declined since iodised salt was introduced in Sweden in 1936. Congenital hypothyroidism, a congenital thyroid hormone deficiency in children, has also sharply declined.
