Low estrogen levels lead to osteoporosis through which mechanism?

• A. Increased osteoclastic activity
• B. Increased osteoblastic activity
• C. Decreased osteoclastic activity
• D. Decreased osteoblastic activity

Answer: (A)

Low estrogen removes inhibitory signals on osteoclasts, tipping the balance of bone remodeling toward resorption. Estrogen normally dampens osteoclast formation and activity and promotes osteoclast apoptosis, while also increasing osteoprotegerin (OPG) to block RANKL signaling. When estrogen levels fall, RANKL signaling rises, osteoclast numbers and activity increase, and bone is broken down faster than it is rebuilt. Over time this accelerated resorption leads to weaker bones and osteoporosis.

If bone formation slowed instead (decreased osteoblastic activity) or osteoclast activity decreased, the pattern of bone loss would differ. The key link with estrogen deficiency and osteoporosis is the rise in osteoclast-mediated resorption.