The easiest way to make the world smarter

TL;DR

Iodized salt is the cheapest, most effective public health tool ever, adding an estimated 180 million IQ points to Americans alone by preventing iodine deficiency.

Key Points

• 1.Iodine deficiency causes goiters and cretinism by starving the thyroid. Without iodine, the thyroid can't produce T3 and T4 hormones, causing it to enlarge into a goiter; in fetuses, deficiency causes irreversible intellectual disability, deafness, and physical stunting called cretinism.
• 2.Salt iodization was pioneered separately in Switzerland and Michigan in the 1920s. Swiss doctors Hunziker and Bayard proved iodized salt eliminated goiters; US doctor David Cowie organized 200 lectures before Morton Salt launched nationwide iodized salt in 1924.
• 3.Iodization added an estimated 180 million IQ points to the US over just 20 years. A 2013 study using WWII draft data found men from the most deficient areas scored one full standard deviation (15 IQ points) higher on cognitive tests after iodization — averaging 3.5 points per American.
• 4.Iodized salt costs only 5 cents per person per year and is technically trivial to produce. It's made by simply spraying a 0.01% potassium iodide solution onto salt crystals during packaging, with no chemical reaction and no meaningful change to the salt.
• 5.The primary iodine source in the US is dairy, not salt or seafood — and it's accidental. Iodine enters milk partly because it's used as a sanitizer for cows and milking equipment; when Australia banned iodine-based cleansers in the 1980s, the entire country became iodine deficient almost overnight.
• 6.US iodine levels have dropped 50% over 50 years, with pregnant women now officially deficient. Median iodine in pregnant US women fell from 327 micrograms/liter in 1971 to just 144 in 2014, driven by rising plant-based milk consumption and processed food companies avoiding iodized salt over taste and branding fears.
• 7.A rigorous double-blind triangle test at America's Test Kitchen showed people cannot taste iodine in salt. Only 3 of 10 expert tasters correctly identified iodized salt in round one, and 4 of 10 in round two — statistically close to random chance — and a review of 34 studies found almost no food changes.
• 8.Despite near-eradication of cretinism, 1 billion people still lack iodized salt and the problem is growing. 23 countries remain iodine deficient today, 5 million babies are born with iodine deficiency disorders annually, and funding and attention are backsliding; pregnant women should supplement with 150 micrograms of iodine daily.