Surprising food gave U.S. a 10-year boost to IQs

Scott Sutherland
July 24, 2013

According to a new study, the United States suddenly got a bit smarter starting in the mid-1920s, and it was due, ironically, to something that we probably don't think about too much about.

When you buy salt at the supermarket, or get those little packets with your take-out food, have you paid much attention to what it says on the packaging? The word 'iodized' on there probably doesn't register to us too often, but it's actually very important. Iodized salt is normal table salt mixed with a small amount of either sodium iodide salt or potassium iodide salt, and it was first introduced in the U.S. in 1924. By adding in these iodide salts, it addressed a serious iodine deficiency in the American diet, which not only reduced the number of deaths due to hyperthyroidism, but also apparently raised IQ test scores in iodine-deficient areas of the country over the next 10 years.

The areas of the U.S. that suffered from iodine deficiency at the time were around the Great Lakes, in the Appalachian region and in the U.S. Northwest, caused simply by not eating enough foods that are high in iodine (such as cheese and cow's milk, eggs, saltwater fish, shellfish). Since salt was and is so widely used, introducing iodized salt filled this deficiency, and the study found that the iodine-deficient regions of the United States saw a 15-point rise in IQ test scores (which translated into a 3.5 point rise nationwide).

This rise in IQ scores has been seen in other nations that introduced iodized salt too. It's called the Flynn Effect, named after Jim Flynn, who documented it and promoted awareness of the problem.

The reason why iodine deficiency affects intelligence is because iodine is used by the thyroid to produce important hormones that affect the development of the brain during childhood, and help the brain and body to function for our entire lives. Iodized salt definitely helps when our normal diet is low in iodine, but you can get more by eating things like bread, soda crackers, eggs, cheese and milk, yogurt, fish (cod or haddock), turkey, beef, soynuts and beans.

According to the World Health Organization, iodine deficiency is still a big problem in the developing world, causing hyperthyroidism, goiter and mental impairment. Their latest stats show that the number of countries that are considered iodine deficient have dropped by half, but some 54 countries around the world still suffer from this problem, and an estimated 33% of households world-wide still don't have access to iodized salt.

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There's several other vitamins and minerals that are (or should be) in our diet that affect our brain development and cognitive ability, such as the B vitamins, vitamins C, D, and E, as well as calcium, iron, magnesium, selenium and zinc. You can try taking a multivitamin to address any deficiencies you might have, but it's probably better to go for foods rich in these nutrients.

The Canadian Heart and Stroke Foundation has a good guide. They recommend fish, such as salmon, rainbow trout, sardines and mackerel. Green vegetables such as kale, collards, chard, spinach and broccoli have magnesium. Whole grains. Nuts like pecans, walnuts and almonds for vitamin E. Fruits that are brightly-coloured red, blue or purple, due to them containing an antioxidant called anthocyanin.

(Photo courtesy: Thomas J. Peterson/Getty Images)

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