Commentary: iodine deficiency as a new challenge for industrialized countries: a UK perspective.

The World Health Organization (WHO) estimates that worldwide 2 billion people, including 285 million school-age children, still have iodine deficiency despite major national and international efforts to increase iodine intake, primarily through the voluntary or mandatory iodization of salt. Iodine deficiency has substantial effects on growth and development and is the most common cause of preventable mental impairment worldwide. Although endemic cretinism had been long recognized to be associated with iodine deficiency, the article from Pharoah, Buttfield and Hetzel in 1971 recognized the importance of severe iodine deficiency and its correction in early pregnancy in a classic interventional epidemiological study. The recent Copenhagen Consensus of 2008 (www.copenhagenconsensus.com) identified salt iodization as the third most important and cost-effective intervention for confronting ten great global challenges. Although the introduction of iodized salt has considerably improved the situation globally in the developing world, iodine deficiency remains an issue in continental Europe where it is estimated that up to 50% of the children live in iodine-deficient communities. Mild iodine deficiency impairs cognition in children, and moderate to severe iodine deficiency in a population reduces the intelligence quotient by 10–15 points. Iodine supplementation pre-pregnancy may prevent this adverse effect on the intellectual development of infants and children. Mild to moderate iodine deficiency occurs in areas that are not immediately recognized as iodine deficient. Iodine deficiency has historically been considered an issue for developing countries rather than industrialized countries such as the UK. Endemic goitre associated with iodine deficiency was at one time widespread in the UK and Medical Research Council surveys in 1924 and 1944 reported visible goitre in up to 50% of the adult women and schoolgirls. No salt iodization programme was adopted in the UK unlike in other European countries. Since the 1940s, significant changes in farming practice in the UK were associated with a rise in the iodine content of milk, particularly during winter months when cattle are dependent on iodine-rich artificial feed. In addition, successive UK governments from the 1940s encouraged increased milk consumption in schoolchildren. By the 1980s, this resulted in the iodine content of milk alone being almost sufficient to meet the recommended daily requirement of 150 mg/day and has been described as an ‘accidental public health triumph’. Although national monitoring of milk iodine content continued, the major concern was to avoid the harmful effects of iodine toxicity rather than deficiency. My interest in thyroid epidemiology was stimulated where as a research fellow in Newcastle-upon-Tyne working with Mike Tunbridge who had led the original Whickham survey documenting the prevalence of thyroid disorders in a representative sample of the UK in the early 1970s. Sixteen percent of the cohort had small but easily palpable diffuse or multinodular goitres. In men, the prevalence of goitre declined with age from 7% in those aged <25 years to 4% in those aged 65–74 years. Among the women, 26% had a goitre; the frequency ranged from 31% in those aged <45 years (mostly diffuse) to 12% in those aged over 75 years (who had a higher proportion of multinodular goitre). In the 20-year follow-up of the Whickham cohort, 10% of the women and 2% of the men had a goitre, as compared with 23 and 5% respectively, in the same subjects at the first survey. The presence of a diffuse goitre was not predictive of any clinical or biochemical evidence of thyroid dysfunction. In women, there was no association between goitre and thyroid antibody status in the initial survey but at the 20-year follow-up, there was a weak association. Although the order in which these Published by Oxford University Press on behalf of the International Epidemiological Association