Final answer:
Calcitonin is the thyroid hormone used to treat osteoporosis because it inhibits osteoclast activity and stimulates calcium uptake by the bones.
Step-by-step explanation:
The thyroid hormone used to treat osteoporosis is calcitonin. Calcitonin is a hormone secreted by the thyroid gland that inhibits osteoclast activity and stimulates calcium uptake by the bones. It reduces bone degradation and helps promote bone density, making it an effective treatment for osteoporosis.