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Iodine deficiency, a public health problem solved decades ago, could be making a comeback due to changing dietary habits, according to new findings from researchers at McMaster University.

Scientists measured iodine levels in urine samples taken from 800 adults in Vancouver, Hamilton, Ottawa and Quebec.

“Iodine is an essential micronutrient that is relevant to fertility, cognitive development and immune health,” says Philip Britz-McKibbin, a professor in the Department of Chemistry and Chemical Biology and lead author of a new study looking at adult iodine levels in some Canadian communities.

Iodine plays a key role in many health functions, as it is necessary for the synthesis of the hormone thyroxine, especially during pregnancy and for child development. Approximately one billion people worldwide suffer from iodine deficiency and it is the leading preventable cause of irreversible cognitive impairment in children.

The results, recently published in the journal Nutrients, showed surprising regional variation in iodine status across Canada.

While residents of Hamilton and Ottawa had sufficient iodine levels, those of Vancouver and Quebec City were more often iodine deficient and had higher exposure to iodine uptake inhibitors, which prevent absorption of iodine by the body.

“It’s a double whammy,” Britz-McKibbin said. “If you have a low dietary iodine intake and are also exposed to ubiquitous environmental inhibitors of iodine uptake like nitrate and thiocyanate, you have an even greater risk of iodine deficiency. Such variations regional levels of iodine deficiency risk among Canadians have never been reported before.”

The team identified three main sources of iodine: iodine supplements, the prescribed hormone thyroxine, and diet.

Iodine is found in very few foods, with the best natural source being seaweed, says Britz-McKibbin. It is also found in seafood, deliberately iodized table salt and in dairy products, by chance.

“Most of the iodine in dairy products comes from hygienic practices. Iodine-based antiseptics are typically used on the teats of cows between milking and leakage into the milk supply,” explains- he. Differences in these practices mean that the iodine content of milk and milk products varies greatly from region to region.

Severe iodine deficiencies rarely occur in Canada. Goiter, a swelling of the thyroid gland in the neck caused by severe iodine deficiency, is not often seen, but the subclinical effects of moderate and mild iodine deficiency are always of concern.

“A major public health achievement has been the prevention of iodine deficiency disorders causing goiter with the introduction of iodized table salt,” says Britz-McKibbin. However, recent food and cooking trends are changing the effectiveness of universal salt iodization programs. For example, more and more people follow vegetarian and vegan diets or use non-iodized salty products, which could deprive them of iodine.

People don’t cook as much at home as they used to, and they eat more processed foods, which may be high in salt but not necessarily iodized salt.

Meanwhile, public health messages suggesting people reduce their sodium intake could limit another source of dietary iodine.

“Reducing salt to extremely low levels can lead to iodine deficiencies, and therefore public health policies targeted at salt reduction should take this unintended harm into account,” says study co-author Salim Yusuf. and Executive Director of Population Health Research. Institute and Emeritus University Professor of Medicine at McMaster.

Britz-McKibbin says a better understanding of iodine is needed, which could come from more regular testing of iodine levels, as excessive iodine intake can also contribute to adverse health effects

“Regular monitoring would allow us to get an assessment of the iodine nutritional status of a population, and public health could change its guidance based on this information,” he says, noting that Denmark, Australia and New Zealand have started fortifying bread with iodized salt. .

“With changes in people’s diets, it may be time to rethink how to improve iodine intake, perhaps by fortifying certain staple foods or beverages that would ensure that most people would ingest adequate levels for optimal health.”