Study finds lower thyroid disease in Gozo. Is it better food or less fireworks?

A study published in the Malta Medical Journal has reported a lower incidence of hypothyroid cases in Gozo than in the rest of Malta. 

However, the authors are suggesting more studies in a bid to establish the reason behind this geographic variation, and whether greater exposure to perchlorate, a byproduct of fireworks but a chemical also found in food packaging, is a contributing factor to higher levels in Malta. 

Hypothyroidism is a common condition where the thyroid gland does not create and release enough thyroid hormone into the bloodstream. This condition can lead to a higher risk of heart disease and heart failure. People with an underactive thyroid tend to develop high levels of low-density lipoprotein (LDL) cholesterol, also known as “bad” cholesterol. 

The most common cause of hypothyroidism worldwide is iodine imbalance related to dietary intake, particularly of heavily processed and frozen foods. 

However, another potential cause of hypothyroidism is perchlorate exposure. Perchlorate is a powerful oxidizing agent used commercially in propellants, in food packaging where its is often used as an anti-static agent, and fireworks. People can be exposed to perchlorate either by inhaling dust or by consuming contaminated food and water. 

The study, which analyzed thyroid function tests (TFTs) from routine or clinically indicated blood testing carried out between 2008 and 2017, reveals that Gozo has a hypothyroid incidence rate of 1,173 cases per 100,000 people 

 In contrast, the incidence rate increases to 1,476 cases in the northern region and to 1,446 cases in the western region. Additionally, a relatively low hypothyroid incidence rate of 1,255 per 100,000 people is reported in the north harbour region. 

According to the authors, the lower rates of hypothyroidism in Gozo may indicate that people living in Malta are more exposed to potential environmental factors, including ‘deficient iodine intake’ or higher perchlorate exposure, both of which are known to be linked to clinical hypothyroidism. 

The consumption of high quantities of packaged foods which include perchlorate could also be one of the dietary factors contributing to the higher hypothyroidism rates in some regions.  

Higher perchlorate in ground water  

The study offers a clue about the lower rates of hypothyroidism in Pembroke, Swieqi, and San Gwann, three adjacent localities in the Northern Harbour District, where potable water is solely sourced from desalinated seawater. 

Since perchlorate levels tend to be much lower in seawater than in groundwater, perchlorate contamination of potable water from groundwater sources might be providing additional exposure to people living in areas where potable water is sourced from both groundwater and seawater. 

Recent studies by chemists Alfred Vella and Colette Pace have revealed significantly elevated levels of perchlorate in both atmospheric and indoor dust, with some areas exceeding recommended limits as determined by the European Food Safety Authority.  

Perchlorate was also found above the detection limit in 44% of groundwater samples tested and 62% of run-off samples collected during the first storms after. 

The study also revealed that localities in the southern area of Malta had an overall higher concentration of perchlorate in dust fall compared to localities in the northern region, with higher levels persisting during the summer and lower concentrations during other seasons. 

In contrast, the current study shows that suburban areas in the western and northern regions, rather than the southern regions, report the highest incidences of hypothyroidism. One possible reason suggested by the authors could be that residents in these areas, including farming communities, tend to consume more locally grown produce potentially contaminated with perchlorate. Further research on consumption patterns in these localities is warranted. 

Surprisingly, these results were not replicated in Gozo, where farming is more widespread than in Malta. This difference could indicate variations in the scale of firework fallout or in the use of food packaging, which is another potential source of perchlorate. 

So far there is no clear explanation for the statistically significant lower levels of hypothyroidism in some localities. In fact the latest study concludes that the lower hypothyroid incidence rates in Gozo now warrants a comparative study “to establish whether this difference is attributable to differing levels of perchlorate exposure from different scale of firework use”. 

The study was written by Tania Cardona from the Superintendence of Public Health, Ian Brincat from the Department of Pathology Mater Dei Hospital, Neville Calleja from Public Health Department, and Roberto Debono, a specialist in Public Health Medicine.

Correction: This article has been amended to correctly reflect the affiliation of Mr Brincat, one of the study authors, to the body he represents.