An Article published Online First and in an upcoming Lancet shows that some 70% of UK school girls are iodine deficient. The highest level of Iodine deficiency was recorded in Belfast (85%). Since developing fetuses are the most susceptible to the adverse effects of iodine deficiency on thyroid function, these findings are of potential major public health importance for the health of these women and any children they may have in future. The Article is by Dr Mark P J Vanderpump, Department of Endocrinology, Royal Free Hampstead NHS Trust, London, UK, and colleagues.
Iodine deficiency is defined by WHO as mild if the population median urinary iodine excretion is 50-99 μg/L, moderate if 20-49 μg/L, and severe if less than 20 μg/L. This study focused on female schoolchildren aged 14-15 years from nine UK centres (Aberdeen, Belfast, Birmingham, Cardiff, Dundee, Exeter, Glasgow, London, and Newcastle-upon-Tyne), since these girls are in the age group who might proceed to pregnancy in the short-to-medium term and are therefore the most susceptible to the adverse effects of iodine deficiency. Girls in this age group attending secondary schools were invited to participate, and members of the survey team made a presentation to participants about the role of the thyroid gland and the effect worldwide of iodine deficiency.
Urinary iodine concentrations and tap water iodine concentrations were measured in June–July, 2009, and November–December, 2009. Ethnic origin, postcode, and a validated diet questionnaire assessing sources of iodine were recorded. The authors found that the median urinary iodine excretion was 80 μg/L. Urinary iodine measurements indicative of mild iodine deficiency were present in 51% of participants, moderate deficiency in 16% and severe deficiency in 1%. Prevalence of iodine deficiency of any level was highest in Belfast (85%), and lowest in the three Scottish centres (52% to 59%) Tap water iodine concentrations were low or undetectable and were not positively associated with urinary iodine concentrations.
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, Higher urinary iodine concentrations were found in the girls in winter, and this seasonal variation may reflect this greater use of iodine-rich winter foodstuffs. Additionally, successive UK Governments from the 1940s encouraged increased milk consumption in schoolchildren. By the 1980s, this approach resulted in the iodine content of milk alone being almost sufficient to meet the recommended daily requirement of 150 μg per day. In this study, low milk intake and high egg intake were associated with lower urinary iodine concentrations. Yet the authors were unable to explain Belfast having the worst results, since diets there were not significantly different to other parts of the UK. Milk consumption has fallen in the UK and as milk iodine levels have remained unchanged, this would suggest that it is the reduced amount of milk being drunk that is responsible for the decline in iodine status. The connection between low iodine status and high egg consumption was unexplained.
Previous research has shown that iodine deficiency can cause significant mental impairment and delayed development in the children of women affected. The authors conclude: "A comprehensive investigation of UK iodine status and evidence-based recommendations on the need to implement a policy of iodine prophylaxis are urgently needed."
In a linked Comment, Dr Elizabeth N Pearce Section of Endocrinology, Diabetes, and Nutrition, Boston University School of Medicine, Boston, MA, USA, says: "It seems unconscionable that a country with the resources of the UK should be iodine-deficient in 2011. How did this happen? The UK, similar to other developed nations such as the USA, and, until recently, Australia and New Zealand, has never mandated iodisation of salt or other foods: less than 5% of salt sold in the UK is iodised."
Dr Pearce calls for mandatory iodisation of salt in the UK, and points to the success of iodisation of salt in commercially baked bread in Australia and New Zealand. She says: "However, it will presumably take some time for public health officials in the UK to develop a comprehensive strategy. Meanwhile, time is of the essence, because children across the UK are currently being born unprotected from the effects of iodine deficiency. Immediate steps should be taken to protect the most vulnerable members of the population. Women who are pregnant, lactating, or planning a pregnancy should be advised to take a daily vitamin containing iodine in the form of potassium iodide."
She concludes: "Whichever method is used for increasing iodine in the UK diet, there needs to be ongoing monitoring of the food supply and of urinary iodine concentrations in the population to ensure that iodine nutrition, once optimised, remains so."
Dr Mark P J Vanderpump, Department of Endocrinology, Royal Free Hampstead NHS Trust, London, UK. T) +44 (0) 203 283 8932 / +44 (0) 7979 545718 E) mark.vanderpump@nhs.net
Dr Elizabeth N Pearce, Section of Endocrinology, Diabetes, and Nutrition, Boston University School of Medicine, Boston, MA, USA. T) +1 617-414-1348 E) elizabeth.pearce@bmc.org
Journal
The Lancet