Iodine deficiency

Iodine, an often overlooked mineral, is crucial in our diet as it is essential for the production of thyroid hormones, along with selenium. While 70% of iodine is primarily found in tissues such as breast tissue, stomach, salivary glands, brain cells, thymus, and arteries, its specific role in these areas is still unknown. Adequate iodine intake during pregnancy is critical for the brain and neurological development of the fetus, which relies on thyroid hormone activity.

Although the UK has traditionally been considered iodine-sufficient, there is growing concern, especially among women of childbearing age and pregnant women, that this may no longer be the case. The standard iodine level ranges from 100-199 micrograms/L, but during pregnancy and breastfeeding, it should be 150-249 micrograms/L.

It is very difficult to estimate the amount of iodine in food. This is because the actual amount of iodine in food varies for several reasons, including iodine content in the soil, farming practices, the season and type of fish. Historically, iodine intake in the UK has been mainly through iodine-enriched feed given to cattle in winter, producing iodine-rich milk. However, organic milk contains over 40% less iodine than conventional milk. Individuals who avoid dairy and fish or consume them sparingly are at risk of iodine deficiency. Vegans and vegetarians may also have insufficient iodine intake, depending on their dairy consumption. Many dairy alternatives, like soya milk, are not iodine-enriched. The recommended daily iodine intake is 150 μg/day, increasing to 200 μg/day during pregnancy and lactation.

The increased iodine requirements during pregnancy are to support the surge in thyroid hormone production in early pregnancy, counter potential elevated renal iodine loss, and provide iodine to the fetus for its thyroid hormone production after thyroid function begins in mid-gestation.

Maintaining sufficient iodine levels during lactation is crucial as postnatal brain development continues, and breast milk iodine concentration mirrors maternal iodine intake.

Low iodine levels in early pregnancy have been linked to children scoring lower in verbal IQ, reading accuracy, and reading comprehension at ages eight and nine. Studies indicate that UK pregnant women may not meet their iodine needs, with some entering pregnancy with insufficient thyroidal iodine stores. Having a good iodine supply before conception leads to a healthier thyroid hormone balance during pregnancy compared to those who increase iodine intake abruptly at the start of pregnancy.

Seaweed has a high concentration of iodine, but it contains variable amounts and intake can lead to excessive iodine. Brown seaweeds (such as kelp) in particular have a very high iodine content. Therefore, it is not recommended to eat brown seaweed or kelp more than once a week, especially during pregnancy. Other seaweeds, such as nori, may have a lower iodine concentration than kelp, but the iodine content varies considerably. Seaweed is therefore not a reliable source of iodine and is not recommended as a means of ensuring adequate iodine intake.

It is important to highlight that there is no specific method to diagnose iodine deficiency in individuals. While urinary iodine concentration can assess a group's status, it is not suitable for individual diagnosis. A dietary evaluation can identify those with low iodine intake, signalling a need for intervention. Many, but not all, pregnancy multivitamin and mineral supplements contain iodine. Iodine in supplements should be in the form of “potassium iodide” or “potassium iodate” and should not exceed the daily adult requirement of 150 mcg.

References

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