Fluoride might stop your thyroid from absorbing enough iodine, which it needs to make hormones—this could make an iodine shortage worse and mess up your metabolism.

Your thyroid gland might soak up more fluoride than other parts of your body, which could make it more likely to get harmed by it.

When kids have more iodine in their urine, fluoride doesn’t seem to make their thyroid gland grow as much—so iodine might help protect their thyroid from fluoride’s effects.

When kids have just enough iodine in their urine but are exposed to more fluoride, their bodies might make less of an important thyroid hormone called TT3 — like their thyroid is struggling a bit under those conditions.

Drinking tea might make it harder for your body to use iodine, which is important for your thyroid to work properly.

Too much fluoride might mess up the thyroid’s ability to handle harmful chemicals in the body, which could hurt the cells that make thyroid hormones and make the gland work less well.