You rely on bones and joints to support your body and help you navigate the world. How do your bones grow, and what happens to them over time?

Rheumatologist Chad Deal, MD, Head of the Center for Osteoporosis and Metabolic Bone Disease, explains.

What bones are made of

Bone is densely packed with flexible fibers (termed collagen), hardened by calcium and phosphorus. They are built to withstand great stress from activities like walking, running and jumping.

How bones change as you grow

Bone is a living tissue that constantly renews itself. “Your skeleton is completely new every 10 years,” says Dr. Deal.

In childhood and adolescence, bone buildup outpaces bone removal, or loss.

In your early 20s, the density of minerals in your bones peaks. Your bone mass may stabilize or start slowly declining as bone loss overtakes bone buildup.

What happens as you age

Natural bone loss accelerates at mid-life. This is especially true for menopausal women, ages 55 to 65, as levels of protective estrogen decline.

“For men, the loss is more gradual because testosterone declines slowly,” says Dr. Deal.

But by age 65, the rate of bone loss evens out for men and women. For the rest of your life, bone mass gradually wanes.

When bones start to thin

If bone thinning makes your bone density drop below normal, you have osteopenia. This silent problem usually causes no symptoms.

“However, it is important to remember that most fractures occur in patients with osteopenia — so early identification, prevention and treatment are important,” says Dr. Deal.

If your bone thinning becomes severe, you’ll be diagnosed with osteoporosis. You may develop symptoms such as back pain, a hunched posture and fractures.

How to safeguard your bones

But you can take steps to keep your bones strong and healthy. Here’s how:

1. Let food fortify your bones. Eat foods rich in calcium and vitamin D.
2. Do weight-bearing exercise. “Heel-strike activities, like walking, will stimulate new bone formation,” says Dr. Deal.
3. Avoid smoking. Smoking will lower your estrogen levels. “It’s also toxic to your cells,” he notes.
4. Get DEXA (DXA) tests. Women should get DXA bone density tests starting at age 65 and men starting at age 70. “If you have clinical risk factors for bone loss or fracture, you may need DXA earlier,” advises Dr. Deal.
5. Take medication, if needed. If you have osteopenia or osteoporosis, certain medications can slow bone loss.
6. Take care of other health issues. Get the care you need for thyroid disorders, parathyroid disorders or any other health condition that affects your bone density.