68% of 14-15 year old girls in UK iodine deficient - health risk for them and their future offspring

Nearly 7 in every 10 girls in the UK aged 14 to 15 years have an iodine deficiency. Proper iodine levels are vital for the healthy development of a fetus. Dr Mark P J Vanderpump, from the Royal Free Hamsptead NHS Trust, London, UK, explained in the journal the Lancet that this is a serious public health concern, not just for the girls, but also their future babies.

85% of the girls tested in Belfast were iodine deficient.

The World Health Organization defines iodine deficiency as:

• Mild – when urinary iodine excretion is 50-99 μg/L
• Moderate – when urinary iodine excretion is 20-49 20-49 μg/L
• Severe – less than 20-49 μg/L

The study measured iodine levels in 14 to 15 year-old schoolgirls in Belfast, Cardiff, Dundee, Exeter, Aberdeen, Birmingham, Glasgow, Newcastle-upon-Tyne, and London. They chose this age group because it preceeds pregnancy in the short-to-medium term, meaning they are the most susceptible to the negative consequences of iodine deficiency.

The participants were given a presentation about what the thyroid gland does, and what impact iodine deficiency has globally.

The researchers measured both urinary iodine concentrations and tap water iodine concentrations in June-July 2009 and November-December 2009. They also gathered details on their ethnicity, postcodes, and validated a diet questionnaire aimed at assessing their iodine food sources.

The researchers found that:

• The median urinary iodine excretion was 80 μg/L
• 51% of the girls had mild iodine deficiency
• 16% of the girls had moderate iodine deficiency
• 1% of them had severe iodine deficiency
• Belfast had the highest level or iodine deficiency at 85%, while three Scottish centers had the lowest with between 52% and 59%.
• Tap water iodine concentrations were either low or impossible to detect, and were not linked in any way to urinary iodine concentrations.

Farming practices which started in the 1940s led to a rise in iodine content in milk. In winter months UK cattle are given feed which is iodine-rich.

The researchers noticed that the girls had higher urinary iodine levels in the winter months, probably because they consumed more iodine-rich foods. Since the 1940s most UK governments have encouraged schoolchildren to consume plenty of milk.

In the 1980s schoolchildren’s daily iodine requirement (150 μg per day) was nearly completely met by milk consumption.

The researchers linked the current high rates of iodine deficiency to low milk and high egg consumption.

However, the author was surprised to find such high deficiency rates in Belfast, because the dietary habits of the girls there were not significantly different from the other girls’.

Most English people, including children drink less milk today than they used to. Iodine levels in milk have remained constant. The researchers believe the current deficiency rate is closely linked to milk consumption.

The authors could not explain why high egg consumption was associated with low iodine levels.

Babies of mothers who were iodine deficient during pregnancy have a high risk of mental impairment and delayed development.

The article ends with the following conclusion:

“A comprehensive investigation of UK iodine status and evidence-based recommendations on the need to implement a policy of iodine prophylaxis are urgently needed.”