Estrogen deficiency contributes to osteoporosis by which mechanism?

• A. Increases osteoblast activity and bone formation.
• B. Increases osteoclast activity and bone resorption.
• C. Reduces calcium absorption from the gut.
• D. Decreases vitamin D activation.

Answer: (B)

Estrogen helps keep bone remodeling balanced by restraining osteoclasts, the cells that break down bone. It does this mainly through the RANKL/OPG system: estrogen lowers the signals (RANKL) that tell osteoclast precursors to become active bone-resorbing cells and increases osteoprotegerin (OPG), which acts like a decoy to block RANKL. When estrogen is deficient, RANKL rises and OPG falls, so more osteoclasts form, survive longer, and resorb bone more aggressively. This boost in bone resorption outpaces bone formation, leading to net bone loss. In addition, estrogen deficiency tends to raise inflammatory cytokines that further stimulate osteoclast activity. The combined effect is the characteristic osteoporosis seen after menopause, with greater loss in trabecular-rich areas like the spine.