Iodine deficiency in the UK - should we take it with a pinch of salt?

Iodine deficiency is now a significant public-health concern in the UK. Data from the National Diet and Nutrition Survey (NDNS; 2019-2023) shows that several population groups are now classified as mildly iodine deficient, including women of childbearing age. This is a change from previous NDNS data where these groups were iodine sufficient. As iodine is needed for thyroid-hormone production, which are essential for brain development, iodine deficiency prior to, and during, pregnancy may have implications for child cognition - including lower IQ. However, the evidence base for the health effects of mild deficiency is not as strong as in severe deficiency. The WHO recommends salt iodisation to control iodine deficiency in a population, but such a policy was never introduced in the UK and iodised salt is not widely available. While UK milk is rich in iodine and is the principal source, the rise in popularity of plant-based milk alternatives may increase the risk of iodine deficiency. It may be necessary to give personalised advice to those with low iodine intake, but identify those at risk is challenging owing to a lack of a biomarker for iodine in an individual. Population-wide approaches may be required in the UK - for example, fortification of bread with iodised salt or mandatory iodine fortification of plant-based dairy alternatives. This review will critically discuss (i) the data on iodine deficiency in the UK (ii) the evidence base for the health implications of mild deficiency and (iii) the potential public-health solutions.