Your skeleton is a living organ — constantly being broken down and rebuilt by cells called osteoclasts (which break down bone) and osteoblasts (which build it back up). In your 20s and into your early 30s, the rebuilding keeps pace with the breakdown. But after about age 30, the balance shifts. The breakdown starts exceeding the rebuild. Bone density begins its gradual, inexorable decline.

Illustration of bone structure showing bone density changes with age

For most people, this slow decline doesn't cause problems. But in some — particularly women after menopause, when estrogen levels plummet and bone loss accelerates — the decline becomes a medical condition called osteoporosis. This weakening of bones makes fractures far more likely, particularly in the hip, spine, and wrist. Hip fractures in older adults are particularly devastating — roughly 50 percent of people who suffer a hip fracture never return to their previous level of independence.

Understanding Bone Density

Bone density peaks around age 30. How strong your bones are at their peak — which is largely determined by genetics, nutrition, and physical activity during your youth and young adulthood — sets the baseline for how much you can afford to lose without crossing into dangerous territory.

Dual-energy X-ray absorptiometry (DEXA) scans measure bone mineral density, particularly in the hip and spine. Results are reported as T-scores: a T-score of 0 means your density matches the peak for healthy young adults. A T-score between -1 and -2.5 indicates osteopenia (low bone mass). Below -2.5 indicates osteoporosis.

Building and Protecting Bone at Any Age

  • Weight-bearing exercise: Walking, jogging, stair climbing, and resistance training all stimulate bone formation. The stress placed on bones during exercise signals osteoblasts to build more bone. The effect is site-specific — running builds leg and hip bone density; upper body resistance training helps the spine and arms.
  • Calcium: Adults need roughly 1,000–1,200 mg of calcium daily. Food sources are better absorbed than supplements — dairy products, fortified plant milks, leafy green vegetables (especially bok choy and kale), sardines, and almonds are good sources.
  • Vitamin D: Essential for calcium absorption. Most people in northern latitudes are vitamin D deficient, particularly in winter. Sunlight exposure, fatty fish, fortified foods, and supplements (particularly during winter months) can help maintain adequate levels.
  • Limit alcohol and smoking: Both alcohol and tobacco use impair bone formation and increase fracture risk. Even moderate alcohol consumption (more than 2 drinks per day) interferes with calcium balance.
  • Muscle mass: Muscle and bone are interconnected. Building and maintaining muscle through resistance training helps maintain the mechanical loading that keeps bone dense.