By Pure Matters

Your bones are constantly changing. Old bone continuously breaks down and is replaced by new. When you're young, your body makes bone fast enough to replace what's lost. This helps you reach your peak bone mass, the point at which your bones are strongest.

At about age 30 (if you're a woman; later, if you're a man), you start to lose bone mass faster than your body can replace it, according to the National Institutes of Health (NIH). This increases your risk for osteoporosis, a disease that causes bones to become less dense. This makes them weak and more vulnerable to breaks. The disease affects 10 million Americans, 8 million of whom are women.

Men begin to catch up to women in rate of bone loss as they age. By ages 65 to 70, men and women lose bone at the same rate, the NIH says. And the ability to absorb calcium, which is important for bone health, decreases for both men and women. Women's bone loss is tied to menopause and the lack of estrogen; for men, osteoporosis is often caused by medications used to treat asthma and rheumatoid arthritis; low levels of testosterone; alcohol abuse; smoking; gastrointestinal diseases that interfere with the body's ability to absorb nutrients; losing too much calcium through the urine; or lack of mobility.

Helping your bones

You can help prevent osteoporosis by including enough calcium in your diet and exercising regularly. Like muscles, bones are living tissue, and exercise makes them stronger. In fact, studies have shown that exercise even may help generate new bone in older adults. Two types of exercise can help build bones:

• Weight-bearing exercises. When your feet and legs bear all of your weight -- as they do when you're walking -- your muscles and bones become stronger because they're working against gravity. Jogging, climbing stairs, dancing, hiking and sports such as tennis, basketball and soccer can benefit your bones, too. Swimming and bicycling are good ways to exercise your heart and lungs, but they don't strengthen your bones because they're not weight-bearing exercises.

• Resistance exercises. Also known as strength training, these types of activities use your muscles to pull or push against something to build bone and muscle strength. Free-weights, weight machines and other fitness tools such as elastic bands, or weights designed to be used in a pool are often used for strength training. To avoid possible injury, be sure to learn the proper techniques for the activity you're doing. Many gyms offer classes, or you can work with a trainer.

In addition to exercise, men and women should make sure they get adequate amounts of calcium and vitamin D; avoid smoking; use alcohol moderately; and talk to their health care provider to find out if any prescribed medications increase bone loss.

Tips to get started

Talk with your health care provider before beginning any exercise program. This is especially important if you have a chronic condition such as heart disease. If you're a woman older than age 65, your provider may recommend a bone mineral density test to screen for osteoporosis. You may need to be tested earlier if you have other risk factors. If you have osteoporosis, your provider may advise you to avoid certain activities and suggest medication to help slow bone loss.