Why do bones become weaker as you age?

As you age, bone remodeling becomes imbalanced. Bones are constantly broken down by cells called osteoclasts and rebuilt by osteoblasts, but after your mid-30s, breakdown starts outpacing formation. This leads to a gradual loss of bone density and mass over time. Several factors drive this. Declining levels of estrogen in women after menopause and testosterone in men accelerate bone loss significantly. The body also becomes less efficient at absorbing calcium from food, and aging kidneys produce less activated vitamin D, which is essential for calcium absorption. Reduced physical activity further weakens bones since mechanical stress is what stimulates bone-building. The result is a more porous, brittle bone structure, a condition called osteoporosis in its most severe form.