Leslie Beck, a dietitian in private practice in Toronto, is director of food and nutrition at Medcan. Follow her on Twitter @LeslieBeckRD
It’s a trace element that you may not think about much.
Due to the mandatory addition of iodine to table salt, severe iodine deficiency rarely occurs in Canada. The salt iodization policy, in effect since 1949, resulted from the widespread presence of iodine-deficient soils in the country.
However, results from a new study from McMaster University in Hamilton, Ontario, suggest that iodine deficiency may be on the rise in parts of Canada due to changing cooking and eating habits.
Here’s what to know about iodine – and why salt iodization may not be as effective as it once was in ensuring adequate levels of the nutrient.
What does iodine do
The body needs iodine to make thyroid hormones. As such, it is crucial for the proper functioning of the thyroid and the control of the body’s metabolism.
Thyroid hormones are also needed to regulate bone and brain development during pregnancy and infancy. And they are necessary for the cognitive development of children from an early age.
Iodine also supports the immune system and plays a role in female fertility.
Consuming too little of the mineral is associated with intellectual disability, stunted growth, infertility, hypothyroidism, depression as well as other iodine deficiency disorders.
Those most at risk of iodine deficiency are pregnant women, young children, people who do not use iodized salt, and vegans or people who consume little dairy.
About the new study
The study, published in the July issue of the journal Nutrientsmeasured iodine levels in 24-hour urine samples from 800 adults, average age 61, living in Vancouver, Hamilton, Ottawa and Quebec.
Overall, 12% of participants were classified as having moderate to severe iodine deficiency.
The researchers also found unexpected regional variations in iodine status. Residents of Vancouver and Quebec had a 2.5 times higher risk of deficiency than those of Ottawa and Hamilton.
In addition to having lower iodine levels, those in Vancouver and Quebec were also more likely to be exposed to higher levels of iodine uptake inhibitors which block the absorption of the mineral by the organism. This “double whammy” puts people at even greater risk of iodine deficiency.
Iodine uptake inhibitors called thiocyanates have been strongly linked to smoking. Other inhibitors, nitrates, had a moderate association with vegetable consumption, particularly green leafy and cruciferous vegetables.
Consumption of dairy products and use of vitamin and mineral supplements containing iodine protected against deficiencies. It is possible that dairy products from Vancouver and Quebec contain less iodine than those from Hamilton and Ottawa, which contributes to a higher prevalence of iodine deficiency.
While dairy products are considered a good source of iodine, the amount varies depending on local health practices. Most of the iodine in dairy products comes from iodine-based sanitizing agents used to clean the teats of cows between milkings, which then leach into milk production.
Changing diet has an impact on iodine intake
According to the researchers, recent cooking and dietary trends are changing the effectiveness of universal salt iodization programs.
The tendency to eat plant-based diets, consume non-dairy milks that are not fortified with iodine, and use non-iodized salts (e.g. sea salt, Himalayan) could be leaving people lacking in ‘iodine. Public health messages to reduce sodium (salt) intake to prevent hypertension may also help reduce iodine in diets.
A diet that contains lots of highly processed foods, although high in salt, will be lower in iodine since the salt used in food manufacturing is generally not iodized.
According to Philip Britz-Mckibbin, lead author of the study from the Department of Chemistry and Chemical Biology at McMaster University, “It may be time to rethink how to improve iodine nutrition, perhaps by fortifying certain basic foods or drinks, which has already been implemented in Denmark, Australia and New Zealand”.
Best sources of iodine, daily needs
One of the best dietary sources of iodine is seaweed (eg, kelp, nori, kombu, wakame), but amounts vary greatly between species. Other food sources include dairy products, fish, seafood, and eggs.
Commercial breads are only a good source of iodine if the manufacturers use dough conditioners that contain iodine. But it’s hard to know since nutrition labels aren’t required to include information about iodine.
Iodine is added to many multivitamin and mineral supplements, often at a dose of 150 mcg, the daily requirement for adults. Gummy multivitamins usually contain much less.
During pregnancy, women need 220 mcg per day, which many, but not all, prenatal supplements contain (check labels). Daily iodine requirements increase to 290 mcg during lactation.
Excess iodine intakes can cause some of the same symptoms of iodine deficiency and should be avoided.
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