Iodine and Intelligence, a Salty Issue.

Did you know we offer a Winter School course in Communicating Science? If you’re interested in science writing for both specialist and non-specialist audiences, presenting to communicate science and the use of emerging online social media in science communication, this is a great course for you. If you’re interested, check out “Communicating Science” in course outlines for more details.

Over the coming weeks we’ll be showcasing blog posts written by Communicating Science students during their course last year. The next blog in the series is “Iodine and Intelligence, a Salty Issue” by Meg Adams.

I love love love salt, I put it on everything (yep even on toast and you can’t keep me away from salted chocolate). Surely that can’t be good for me, right? Consuming too much salt can cause an increased  blood pressure and increase the risk of cardiovascular disease including heart, stroke and blood vessel disease.

But what about the benefits? Up until the 1920s salt was made without being iodized so obviously iodine (a nutrient found in soil and seawater) deficiency numbers were a lot higher as table salt is the main source of this micronutrient today. Iodine deficiency is not only the leading cause of preventable mental disintegration but also thyroid (endocrine gland in lower front of the neck) issues:

Goiter Thyroid progressively gets a lot bigger as it tries to keep up with the demand for hormone production. Patients with large goiter can often choke when lying down and have difficulty swallowing and breathing…. plus they look like those gibbon moneys when they get real mad!
Hypothyroidism- An underactive thyroid gland, as the bodies iodine levels fall hypothyroidism can develop.

The World Health Organization estimates that nearly a huge 50 million people suffer some degree of mental impairment due to iodine deficiency, and that this is the leading cause of preventable mental retardation in the world. Many years ago in developed countries the effects of micronutrient deficiencies are quite significant. Lack of vitamin D in industrial cities has caused people to develop rickets, populations dependent on maize often develop pellagra due to inadequate niacin and iodine deficiency. Dietary improvements and food fortification has eliminated these problems.

The most important effects of iodine deficiency are on the cognitive development of fetuses in utero, and these effects are not reversible later on in life. So really anyone would expect the benefits of iodization in terms of adult health to be evident only many decades after the rollout of the iodization intervention. Iodine deficiency also plays a large role geographically, for example, in India the problem is there are low levels of iodine in the soil which can easily be fixed by iodine fortified salt but it’s costly which means it’s believed that approximately 350 million Indians do not consume it.  Because iodine deficiency affects mental development, it is thought to be a pretty good explanation for this concept called the Flynn effect.

The Flynn effect is the substantial and long-sustained increase in both fluid and crystallized intelligence test scores measured in many parts of the world from roughly 1930 to the present day.

A study that used military data collected during WWI and WWII compared groups born before and after the iodization of salt. The results found that the intervention raised IQ by approximately one standard deviation and can explain roughly one decade’s worth of the upward trend in IQ in the US (the Flynn Effect). There are also a number of other studies that support this!

So perhaps my love for salt isn’t so bad after all? Smarter than my grandparents.


J. Freyer et al. The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States. Department of Economics, Dartmouth College. Feburary 27 2009.

O. Balch. ‘Life-saving’ bindis and iron fish: original health ideas for poorer countries. The Guardian. July 3 2015.

American Thyroid Association. Iodine Deficiency.June 4 2014

Piccone. The Silent Epidemic of Iodine Deficiency.Life Extension Magazine. October 2011

The Heart Foundation. Salt.

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