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26.05.2025

Iodine deficiency threatens vegetarian thyroid

Cutting meat from your diet increases your risk of developing an underactive thyroid, or hypothyroidism. This was discovered by Austrian epidemiologists who analysed British data. Eliminating meat reduces iodine intake. And selenium intake, for that matter.

Study
Austrian researchers, affiliated with the University of Vienna, analyzed data from 466,362 Britons collected in the UK Biobank project. The Austrians characterized the diet of the Britons based on their meat intake and then looked at whether they developed an underactive thyroid gland over a period of almost 13 years.

In the group as a whole, this happened in 10,831 study participants. So we are talking about a chance of 2.3 percent.

The reason for the research was the studies in which vegetarians and vegans sometimes get very little iodine. The thyroid gland uses iodine as a raw material for thyroid hormone.

Results
The two largest groups in the population studied were the Brits who ate a lot of meat and the Brits who ate little meat. These two groups were about the same size. Together, these two groups made up 95 percent of the study participants.

The poultry-eaters, fish-eating vegetarians or pescetarians, and fish-avoiding vegetarians each accounted for 1-2 percent.

The vegans were so small in number that their share was negligible. The Austrians found a trend that vegans were more likely to be hypothyroid than heavy meat eaters, but the difference was not statistically significant. This was probably because there were few vegans in the researchers' database.

In the other groups - the low-meat eaters, the chicken eaters, the pescetarians, and the other vegetarians - the chance of an underactive thyroid was higher than in the heavy meat eaters. This was especially the case for the vegetarians.

Iodine
When the researchers looked at the daily intake of iodine, it became clear what increased the chance of a slow-working thyroid in vegetarians. The intake of iodine in this group was low. This is not so strange. In the Western diet, meat is an important source of iodine.

The figure below relates to an average intake. In 2014, the European EFSA concluded that adults need 150 micrograms of iodine daily. [EFSA 2014;12(5):3660.]

If you look at the percentage within a group that gets too little iodine, vegans and vegetarians score poorly. In these two groups, 93 and 44 percent respectively consume less than 150 micrograms of iodine per day.

Selenium
The researchers do not mention selenium. However, there are indications that a selenium deficiency can also cause an underactive thyroid gland. [Int J Endocrinol. 2017:2017:1297658.] [Am J Clin Nutr. 1993 Feb;57(2 Suppl):271S-275S.]

The table below - click on it for a larger version - that we found in the supplementary data section of the Austrian study shows that the average intake of selenium was too low in all groups. In the vegetarians and vegans it was even alarmingly low.

According to EFSA, adults should consume 70 micrograms of selenium daily. [EFSA J. 2014;12(10):3846.] Even among heavy meat eaters, the average intake is below that.

Supplementing
Perhaps vegetarians and vegans should supplement not only with iodine, but also with selenium. And of course with vitamin B12. And perhaps with much more micronutrients. [McCarty MF. 'Failure to Thrive' as a Vegan – Could Supplemental Carninutrients Help?] But that's another story.

Source:
BMC Med. 2025 May 7;23(1):269.

More:
You can expect these health effects if you replace meat with meat substitutes 16.04.2024
Higher consumption of meat, longer life 04.08.2023
The fragile bones of the flexitarian 18.04.2023
Is the carnivore diet unhealthy? 16.02.2022

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