Tasmania is the butt of more jokes than anywhere else, but one has a backstory

For more years than we can remember, Taswegians have copped the jokes about inbreeding due to the state's small and isolated population.

But the most solid theories about the source of the two-headed people have nothing to do with a small gene pool.

Old myths and fictional tales can sometimes signal more serious subjects, as Dr Kristen Hynes knows all too well.

Dr Hynes is a research fellow with the University of Tasmania's Menzies Institute for Medical Research and has spent much of her career looking at iodine deficiency and the health implications it has had in the state; a condition that has direct links to the taunt about Tasmanians having two heads.

She said iodine deficiency is a serious issue and the lack of the micronutrient during pregnancy can affect a child's literacy skills or during adulthood and can result in the development of goitres.

"While mainlanders may tease that Tasmanians have two heads, the taunt has a serious side," Dr Hynes said.

"One explanation for the emergence of the two-headed Tasmanian myth is the widespread occurrence of goitres during the 19th and 20th centuries in the Tasmanian population that resulted from lack of iodine in the diet.

"Left untreated, some of the goitres were so big that they did look like another head. Treatment involving surgical removal left people with a scar along their neck; another bit of fiction about how you can tell that someone is from Tasmania.

"While we can laugh at this silly myth, it does point to a serious health issue that remains with us today."

Tasmanian soil is iodine deficient, said to be caused by the combined effects of Tasmania's mountainous terrain and weather patterns.

Dr Hynes said there was no evidence that Aboriginal people, before European arrival, had iodine deficiency disorders.

"It's about 30 years after Europeans arrived that we start seeing evidence of goitres appearing, in particular among younger people who had grown up in Tasmania and had been subjected to iodine deficiency for most of their lives. And there have been issues in Tasmania ever since," she said.

"For most of the population, thanks to successful public health initiatives such as mandatory fortification of bread with iodised salt, iodine deficiency has been largely eliminated. There are still groups in the community, however, who remain at risk of iodine deficiency and its associated disorders.

"It is particularly important that pregnant and breastfeeding women, and those planning pregnancy, receive adequate iodine as part of their diet. Our research has shown that children born to mothers who were iodine deficient during their pregnancy had poorer outcomes in some NAPLAN tests.

"From the earliest tests in Year 3 through to Year 9 those children had lower results for literacy, particularly spelling, compared to children whose mothers were not iodine deficient during pregnancy.

"Despite these children having adequate iodine nutrition in childhood, there was no closing of the gap in education outcomes as they got older."