No bones about it, the statistics about osteoporosis are staggering: The condition, which causes bones to become fragile, afflicts some 10 million Americans.

About half of all women and one-fourth of men will have an osteoporosis-related fracture at some point in their lives. An estimated 300,000 people break a hip every year.

But debilitating bone loss and fractures are not inevitable. Even if you have osteoporosis or its milder cousin, osteopenia, you can — and should — take measures to protect your bones. “It’s not too late,’’ says Chad Deal, MD, head of the Center for Osteoporosis and Metabolic Bone Disease at the Cleveland Clinic. “It’s never too late.’’

Our bones are always changing, as new bone forms and old bone is broken down and removed. When we’re young, bone formation occurs at a faster pace than removal does, allowing our bones to become larger and stronger. This begins to change in our thirties, with bone mass remaining stable in some adults and gradually declining in others.

Bone loss accelerates in women immediately after menopause. Men, too, experience a decline in bone strength beginning in midlife. Smoking, drinking too much alcohol, eating disorders such as anorexia and bulimia, and some medications such as steroids can speed up bone loss even more.

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Wow Fact

Nearly three-fourths of American children aren’t getting enough vitamin D, a nutrient necessary for bone growth. Millions of adults — including at least 40 percent of seniors — also have a D deficiency, increasing their risk for osteoporosis, or exacerbating the condition if they’ve already been diagnosed with it.

For some people, the loss leads to osteopenia. This means you have below-average bone density and a higher risk of bone fractures, but you won’t necessarily go on to develop osteoporosis. Osteoporosis occurs when bones become so porous they look like Swiss cheese, and so brittle that the slightest trauma may crack them.

Osteoporosis and osteopenia generally cause no noticeable symptoms, and many people don’t realize they have these conditions until a bone breaks. Bone density testing can detect a problem before a fracture occurs.

When women hit menopause, they should ask their doctor about getting tested, and men should do so once they turn 50, Dr. Deal says.

If you have osteoporosis, your doctor may prescribe medication to stave off further bone loss. Several drugs are approved for osteopenia as well as osteoporosis, though many people with osteopenia may not need medication.

Whether or not you’re on medication, regular exercise and a good diet — especially getting enough calcium and vitamin D — are essential for keeping your bones as strong as they can possibly be and for improving your strength and balance — your best bets against a bone-breaking tumble.

QUIZ: How Physically Active Are You?