Iodine

Iodine prophylaxis in Italy: the 2015-2019 ISS data

Italy has achieved iodine sufficiency and goitre has disappeared among school-age children: these are the key findings in the ISTISAN report “Monitoring of iodine prophylaxis in Italy - 2015-2019 data”, published by the ISS on the occasion of the International Thyroid Awareness Week (24-30 May). The report presents the results of a surveillance study carried out by the National Observatory for the Monitoring of Iodine Prophylaxis in Italy (OSNAMI) of the ISS, in collaboration with the Regional Observatories for Goitre Prevention.

Tests performed

Participants included about 4,000 children aged 11-13 years living in both rural (48%) and urban (52%) areas (sentinel or reference areas, respectively) of Liguria, Emilia-Romagna, Veneto, Tuscany, Umbria, Marche, Lazio, Calabria and Sicily. An ad hoc questionnaire on iodized salt consumption was administered to all participants, who also underwent a medical examination, and a spot urine sample was collected to determine urinary iodine concentration (UIC).

Goitre frequency among school-age children was assessed by thyroid ultrasound in seven regions (Liguria, Emilia-Romagna, Tuscany, Umbria, Marche, Lazio, Sicily).

In the three regions that were found to be iodine sufficient in the first surveillance study (2007-2012, 7,455 children), i.e. Liguria, Tuscany and Sicily, the frequency of thyroid hypoechogenicity was also assessed, as an indirect marker of autoimmune thyroiditis.

Neonatal TSH levels were analyzed in collaboration with the Regional Neonatal Screening Centres for Congenital Hypothyroidism of five regions (Lombardy, Veneto-Verona, Emilia-Romagna, Marche, Calabria). A frequency of high neonatal TSH concentrations (>5,0 mU/L) below 3% is indicative of iodine sufficiency in the target population.

Findings

The national median UIC was 124 µg/L, which indicates iodine sufficiency. In addition, no difference was observed in terms of median concentrations between rural and urban areas (130 µg/L and 120 µg/L, respectively). A comparison with the first study confirms the elimination of iodine nutrition deficiency in Tuscany, Liguria and Sicily, and the achievement of iodine sufficiency in the other six regions.

Goitre frequency was estimated in seven of the nine regions taking part in the study (Liguria, Sicily, Tuscany, Emilia-Romagna, Umbria, Marche, Lazio). It was found to be <5% across all the regions and just above 5% in rural areas of Umbria (5.4%, compared to 3.9% in urban areas). According to the World Health Organization (WHO), a frequency above 5% is indicative of endemic goitre.

When the prevalence of high neonatal TSH (thyroid-stimulating hormone) levels, i.e. >5,0 mU/L, does not exceed 3% (blood samples collected 3 to 4 days after birth), the neonatal population, and indirectly pregnant women, are considered iodine sufficient. In Italy, neonatal TSH levels are determined for all newborns as part of neonatal screening for congenital hypothyroidism. OSNAMI analyzed TSH data for over 1 million children born between 2004 and 2018 and found that the prevalence of high TSH levels (>5,0 mU/L), while still above the 3% threshold, was declining significantly (6.1% in 2010 vs 4.9% in 2018). Although encouraging, these findings suggest that pregnant women in our country remain at high risk of iodine nutrition deficiency.

The OSNAMI monitoring also aims to assess possible adverse effects of the prophylaxis programme, such as increased incidence of hyperthyroidism and autoimmune thyroiditis. Prescriptions of anti-thyroid medications declined by 7.4% at national level between 2001 and 2018 (min -0.8%; max -16.5%), which indicated, albeit indirectly, a progressive reduction in the incidence of forms of hyperthyroidism caused by autonomous thyroid nodules, as a result of improved iodine nutrition in the population. In addition, in the three regions that were found to be iodine sufficient in the first study (Liguria, Tuscany and Sicily), the frequency of thyroid hypoechogenicity was assessed, as an indirect marker of autoimmune thyroiditis: average frequency was 6.6%, but percentages were significantly lower in adequate-weight children (4.4%) compared to overweight (11%) and obese (24.1%) children. These results provide a baseline for monitoring the frequency of thyroid hypoechogenicity in areas that have been iodine-sufficient for at least 10 years, and highlight the importance of assessing body mass index (BMI) as a potential confounder.

Conclusions

Iodine sufficiency has been achieved in Italy 15 years after the approval of Law 55/2005, which introduced the national iodine prophylaxis programme and regulates the sale and use of iodized salt. This important result was obtained despite the fact that salt consumption among Italians has been declining in recent years (-12%), which confirms that iodine content in the salt sold in our country (30 mg/kg) is, at least for the moment, sufficient to make up for that decline. While representing a major public health success, iodine sufficiency is only a first step in the long process of consolidating the national iodine prophylaxis programme. The country should now aim to ensure the sustainability of the programme. Effective measures will be required to achieve this objective, such as ensuring proper training of healthcare professionals and raising people’s awareness of strategies to prevent iodine deficiency disorders. More extensive and accurate monitoring will also be needed, with involvement from all the regions and the groups most at risk of iodine deficiency, such as pregnant women, for whom national-level epidemiological data are not yet available.