Iodine is a trace element required for thyroid hormone production. Requirements increase in pregnancy, when even mild deficiency may affect offspring neurocognitive development.
The gold standard for assessing iodine status is population surveys of urinary iodine concentration (UIC). The WHO also suggests a population prevalence of >3% of TSH values > 5 mIU/L indicates deficiency. A recent UK survey of 700 teenage girls demonstrated mild iodine deficiency (median UIC 80 μg/L; sufficiency > 100) with seasonal variation. We recently demonstrated iodine deficiency in 240 pregnant women in Belfast associated with poor dairy intake.
We surveyed 903 girls aged 1415 years in seven sites across Ireland with spot urine collections and iodine specific food frequency questionnaires. We also sampled a range of milk available for sale at each site bimonthly including organic brands. The median urinary iodine concentration (UIC) was 111μg/L. All areas were sufficient except Galway (98μg/L). A positive correlation was found between UIC and milk consumption estimated from (P<0.001). In the two sample sites surveyed twice UIC levels were lower in summer vs winter months (P=0.005).
Milk samples collected from Galway and Roscommon had a lower mean iodine concentration compared to those from Derry/Londonderry (P<0.05). Organic milk had similar levels to nonorganic milk.
Neonatal blood spot TSH results of all 354,403 infants born in NI between 20002014 were also reviewed and 0.5% of neonates had a TSH > 5 mIU/L. Higher TSH levels were found in babies born during summer months.
These analyses suggest iodine sufficiency in Ireland, although of borderline degree. Altered eating habits in pregnancy, along with seasonal and geographical factors may combine to increase the risk of iodine deficiency. Continued population monitoring and pre-pregnancy education is required in the British Isles while there remains no iodine fortification program.