Why Cruciferous food is bad for Hypothyroidism?

If you have hypothyroidism (underactive thyroid), you may have been told to avoid cruciferous vegetables  such as

1. kale.
2. cauliflower.
3. broccoli.
4. cabbage.
5. Brussels sprouts.

These vegetables have been shown, in certain situations, to interfere with how your thyroid gland uses iodine.