Iodine
A trace element essential for making thyroid hormones, whose deficiency is the leading preventable cause of intellectual disability in the world.
Iodine is essential for the synthesis of thyroid hormones (T3, T4), which regulate metabolism, growth, brain development and body temperature. The body does not make it; it has to come from food.
The original angle (iodised salt, a public health victory): iodine deficiency historically caused goitre (a swollen thyroid) and cretinism (severe intellectual disability in children). The iodisation of table salt, widespread in the 20th century, is one of the most effective public health measures in history: it caused these conditions to plummet.
But a return of deficiency is being seen in some countries, paradoxically because of “good” trends:
- The fashion for non-iodised salts (fleur de sel, pink Himalayan salt) which, unlike standard table salt, are not iodised
- The general reduction in salt (the anti-hypertension message)
- The avoidance of dairy products (a source of iodine) among vegans
Main sources: sea fish, shellfish, seaweed, dairy products, eggs, iodised salt.
The opposite trap (excess): too much iodine (too much seaweed such as kombu, which is very concentrated) can also disrupt the thyroid. Asian seaweeds can contain massive doses. The balance is narrow.
At-risk groups: pregnant women (higher needs, crucial for the baby’s brain), vegans, and heavy users of non-iodised “gourmet” salts. Pregnancy is the most critical period: a deficiency can affect the child’s cognitive development.