Postmenopausal osteoporosis occurs largely due to decreased levels of which hormone?

• A. Calcitonin
• B. Estrogen
• C. Parathyroid hormone
• D. Vitamin D

Answer: (B)

Estrogen keeps bone density in check by dampening bone resorption. After menopause, estrogen levels fall sharply, so osteoclast activity rises and bone remodeling tilts toward resorption. This increased bone turnover, especially in trabecular bone of the spine and hip, leads to the net loss of bone mineral density seen in postmenopausal osteoporosis. Mechanistically, lower estrogen heightens RANKL signaling and reduces osteoprotegerin, promoting osteoclast formation and activity.

Calcitonin lowers osteoclast activity but its deficiency isn’t the driving factor here. Parathyroid hormone raises calcium by increasing bone resorption, but the question focuses on the menopausal pattern driven primarily by estrogen loss. Vitamin D deficiency affects mineralization (osteomalacia) more than the typical postmenopausal osteoporosis pattern, though it can contribute to bone loss.