Iodine in table salt: How a public health victory is becoming a victim of its own success

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Whether it's kosher, Himalayan pink or sea salt, Canadians have a wide range of choices when it comes to salts.

But what many of these don't have — or don't have much of — is iodine. The mineral is essential for the body to make thyroid hormones, but can be rare in many parts of the world. And researchers say it's time for Canadians to pay attention to how much iodine they're getting.

Table salt is one major source of iodine in Canada. In 1949, the government made it a mandatory additive. While Canadians can also get their iodine in by eating seafood (seawater is an abundant source of iodine) and dairy (farmers often use iodine-based antiseptics on udders), much of the soil in Canada is iodine-deficient — which means the crops and fruits that grow from our soils often are, too.

Not having enough iodine could lead to a variety of health conditions, like goitres — a large, usually benign swelling of the thyroid gland — which used to be quite common in parts of Canada. It's still commonly seen in inland countries in Asia and Africa that don't add iodine to the food. 

Another, more serious, irreversible condition commonly caused by iodine deficiency is congenital iodine deficiency syndrome, also known as cretinism. It happens when a fetus doesn't get enough iodine while in the womb, and can cause stunted physical and mental growth.

It's become very rare in North America and the developed world. But Dr. Anna Banerji, a pediatrician at Unity Health Toronto, and chair of the North American Refugee Health Conference, says she recently saw a case of a 17-year-old who had moved to Canada from an iodine-poor country.

"She was about this tall," said Banerji, gesturing around three feet, "had the classical face of cretinism and was intellectually delayed — severe, severe intellectual deficits."

She says it's easy for Canadians to forget the importance of iodine because serious deficiencies like this are so rare, thanks to public health measures — like having iodine added to table salt. It's still in our salt, but Canadian dietary patterns have changed, she says, raising concerns of a comeback. 

"We eliminated iodine deficiency, cretinism, goitre, and all that in general in many parts of the world, and we don't see it anymore, it's off the radar," she said. 

"I think it's a [victim] of its own success," Banerji said. In Canada, she says, the problem could be coming back, as dietary habits have changed

Iodine deficiency appears to be on the rise across North America, say researchers. 

A 2022 study out of McMaster University in Hamilton found 11.9 per cent of the Canadians they monitored had a moderate to severe deficiency. 

The authors, who looked at iodine levels collected from 800 participants in four clinical sites across Canada, say recent public health policies that call for people to reduce their sodium and dairy intake may also have inadvertently reduced iodine intake.