Thyroid hormones seem to turn up the activity of a bone-building enzyme in rat bone cells, even at low levels—kind of like a volume knob for bone growth.

Thyroid hormone might directly boost a bone enzyme in lab-grown rat bone cells at levels seen in people with an overactive thyroid, which could explain why those patients often have high bone enzyme levels.

In rat bone cells, how strongly different thyroid hormones stick to their receptors matches how active they're known to be — suggesting these receptors actually do something important in how thyroid hormones affect bones.

Rat bone-building cells have special spots inside their control centers that grab thyroid hormone very tightly, and each cell has room for about 2,000 of these hormone connections.

When someone has an overactive thyroid, their high alkaline phosphatase levels are usually because of faster bone turnover, not liver problems — thyroid hormones speed up how bones break down and rebuild.