Iodine in the UK: the end of an “accidental public health triumph”

Taylor P, Prentice M, Dias R et al. Iodine in the UK: the end of an “accidental public health triumph” The Lancet Diabetes & Endocrinology, 2026; 0

DOI: 10.1016/S2213-8587(26)00271-8

Endemic goitre persisted into the 20th century, and unlike almost every comparable country, the UK never iodised its salt. Sufficiency arrived, instead, by accident: from the 1950s, the use of iodophor disinfectants in dairy processing and iodine-enriched cattle feed increased the iodine content in milk enough to sustain adequacy, which has been called an “accidental public health triumph”.[1] That accident is now unwinding, as the latest National Diet and Nutrition Survey (NDNS) shows.[2]

The NDNS has measured urinary iodine concentration (UIC) since 2013, reporting significant annual declines in girls aged 11–18 years (−3·4%) and adults aged 19–64 years (−2·9%).[2] Among women of childbearing age, median UIC has decreased by 30%, from 117 μg/L to 82 μg/L, which is less than the WHO sufficiency threshold of 100 μg/L. Reliance on the median understates the problem: the proportion of these women with levels less than 50 μg/L has nearly tripled (from 11% to 30%, against a WHO ceiling of 20%, which has been breached since 2016), whereas the 20th percentile has decreased by 43%. Women with the lowest concentrations are at greatest risk: deficiency of this degree risks goitre in women and impaired neurodevelopment in their children.

Risk is concentrated in identifiable, vulnerable groups.[3] In two small cross-sectional samples of vegans in Nottingham, UK (n=12 in 2016–17 and n=7 in 2019), median UIC was 31 μg/L and 12 μg/L, respectively, the latter within the WHO severe deficiency band.[4] Plant-based diets are adopted fastest by adolescent girls and young women, who are the most iodine-insufficient group. Iodine status in pregnancy is largely unknown: NDNS excluded pregnant women until its current fieldwork period. Regional cohorts show a median first-trimester UIC of 60–100 μg/L against a WHO threshold of 150 μg/L and, in Bradford, gestational goitre in 36% (89/246) of women.[3]

The causes of this decline are clear. Cows’ milk supplies 30–40% of the UK population's iodine intake, and consumption has decreased as plant-based alternatives have displaced it; fewer than half of plant-based milk alternatives are fortified with iodine, and plant-based yoghurt or cheese alternatives almost never include iodine.[5] Milk typically contains higher iodine content in the winter than in the summer; however, iodine content in recent winter milk has decreased compared with that in 1996,[6] and iodophor use in dairy processing has decreased, undoing the accident that made Britain iodine-replete. None of these changes were assessed for their effect on population iodine status: there is no iodisation mandate, no labelling requirement, no clear periconceptional guidance. In 2014, the Scientific Advisory Committee on Nutrition (SACN) acknowledged iodine deficiency among girls and women of reproductive age but had no national data; the UK is now one of only two European countries monitoring iodine status, and those data show a decade of decline.

Denmark's mandatory iodisation in 2000 lifted median UIC from 61 μg/L to 101 μg/L; two decades of surveillance recorded declines in goitre, nodules, and thyroid volume, with only a transient increase in hyperthyroidism among older adults, resolving to levels below baseline within 20 years.[7] Adolescents born after iodisation also showed higher educational attainment.[8]

Timing matters: the fetus depends entirely on maternal thyroxine until its thyroid matures at around 20 weeks’ gestation, a window that includes the weeks before pregnancy is recognised. In the Avon Longitudinal Study of Parents and Children, children of mothers with an iodine-to-creatinine ratio of less than 150 μg/g were more likely to score in the lowest quartile for verbal IQ and reading at age 8–9 years than children of mothers with a ratio of 150 μg/g or more.[9] The only UK economic modelling study of iodine supplementation in pregnancy found net savings from supplementation in pregnancy of £199 per woman to the National Health Service and £4476 to society.[10] Across approximately 650 000 annual births, of which of which about 30% are to iodine-insufficient women, inaction plausibly costs approximately £900 million per birth cohort in foregone human capital.

In our opinion, three strategies are needed. First, the NDNS must continue to include pregnant women in its annual urinary iodine measurements, with sentinel antenatal monitoring alongside. Second, the relevant Royal Colleges should recommend 150 μg/day periconceptionally, in pregnancy and during lactation. Finally, salt used in bread manufacturing should be iodised by mandate, and plant-based milk alternatives held to a minimum iodine standard, with post-implementation thyroid surveillance. SACN's plan to revisit iodine is welcome, but it is no reason to defer.

Communication must correct the assumption that iodine deficiency is only a problem for low-income countries and reach adolescents and plant-based consumers. Targeted outreach is needed for the groups universal measures reach last: vegans, low-income and ethnic-minority women, and pregnant teenagers. A cross-departmental UK Iodine Taskforce, publishing annually and accountable to the UK Parliament, should aim to address the problem.

A regulatory precedent already exists. In 2024, after three decades of deliberation, the UK legislated for folic acid fortification of flour. The case for addressing iodine deficiency is just as strong, given that the nutrient shortfall is greater and the cost of delay is already documented in a decade of biomarker data. Britain got lucky once, but luck is no substitute for governance: the neurodevelopment of the next generation should not be left to chance.