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Thursday 18th July 2019

Warning to vegans over iodine

7th June 2011

Vegan diets probably do not make enough provision for iodine, leaving many vegans iodine-deficient, according to a recent US study.


Iodine is an element usually found in seafood, eggs, and dairy, and it is essential to human health.

Due to its relative rarity, iodine is also commonly added to salt, though not all brands of salt contain it.

The researchers said that their finding would be particularly relevant for pregnant women who were vegans.

For the study, the researchers found 140 mostly female vegetarian and vegan study subjects.

The researchers took urine samples from the women and measured levels of perchlorate, thiocyanate, various thyroid hormones, and iodine itself.

Perchlorate and thiocyanate are both thought to interfere with the functioning of the thyroid gland.

The researchers measured an average iodine level of 147 microgrammes in vegetarians and 79 in vegans, meaning that vegans were the recommended levels set by the World Health Organisation (WHO).

The WHO recommends a minimum amount of 100 microgrammes of iodine per litre of urine, and it also recommends a minimum of 150 microgrammes per litre for pregnant women.

Although iodine levels differed greatly between vegans and vegetarians, thyroid hormone levels were both within the normal range.

Unfortunately, doing a urine test for iodine does not provide a long-term picture of a person's iodine intake.

Robert Smallridge, an endocrinologist at the Mayo Clinic in Jacksonville, Florida, who was not involved in the new research, said he believed the finding was interesting, and that it deserved people's attention.

He said he felt it was important that the researchers had identified an iodine-deficient group.

Iodine-deficiency in vitro and in early childhood is one of the leading preventable causes of mental disabilites in children.

Lead researcher Angela Leung, an assistant professor of medicine at Boston University in the US,  said that scientists had not really asked themselves whether or not vegetarians and vegans were more likely to be iodine deficient.

The researchers also did not find any link between thyroid hormones and levels of perchlorate and thiocyanate in the urine.

Leung said that the purpose of her study was to pave the way for future research and to further public awareness, and that all women of childbearing age should be encouraged to take iodine supplements.

She said that, in particular, vegan women of childbearing age should be encouraged to take iodine supplements.

Too much iodine can cause problems, however, and the WHO recommended limit for iodine is 249 microgrammes per litre in pregnant women, and 200 microgrammes per litre in other people.

Sarah Bath, a PhD student at the University of Surrey, who did not participate in the new study, said that in countries where people usually got enough iodine, there was an overriding assumption that everyone was getting enough.

In a separate, related study, about half of all female adolescents in the UK had a mild iodine deficiency.


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