Why is potassium iodine only effective in people under 40?

Question

My country started distributing potassium iodine tablets to take in case of a nuclear accident or attack, but only to those under 40 years old (with prescription). Why? What happens at 40 so the pills are bo longer useful?

In: 1

Answer 1

It’s triage.
They are still useful to people over 40 if the radiation dose is high enough, but they are more useful to people under 40.
The thyroid is more active and cells are generally more active under 40. Radiation disrupts this and can lead to higher cancer risks or issues if the thyroid is destroyed. Where as the chance of thyroid cancer from radiation generally goes down at around 40 since the thyroid becomes less active with age.

So the drugs are generally more targeted to the most vulnerable populations first.