Iodine deficiency is often seen as a problem of the past, but this isn’t entirely true. During the 20th century, the iodization of salt became one of the most effective public health interventions for preventing conditions caused by a lack of this mineral, including goiter (enlargement of the thyroid gland) and preventable damage to neurological development.
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Natural sea salt doesn’t have enough. You’re right that it needs to be added, and it really doesn’t take much. We’re talking 150 micrograms per person per day.
And for people who know chemistry, micrograms of something as atomically heavy as iodine is a miniscule amount of a compound… If you had a chunk of physical iodine you could see with your naked eyes, it would probably be enough for 1-3 months of healthy iodine intake.