Skeleton key: take charge of your bone health now.

In the summer of 2003, Clare Egan discovered that she's not invincible. A star runner in Cape Elizabeth, Maine, Egan, now 18, took that June off after track season and then suddenly began running six miles a day. Within a few weeks, "my shin would throb when I ran and after," she says. "It killed." A bone scan revealed that Egan had a stress fracture, which is a slight break in a bone caused by too much repeated impact.

"Cardiovascularly, I was fine, and my muscles could handle the big increase in running," she says, "but I learned my bones weren't ready for it." To let the bone heal, Egan didn't run for several weeks. During that time, she became more conscious of her bones' health and altered her diet to include more calcium. Egan hasn't had a problem since.

Supporting Yourself

Skeleton neglect can profoundly impact your health. But if you do right by your bones, as Egan has done since her injury, they will enable you to succeed at your favorite activities, now and in the future. Bones are made up of living, growing tissue that gets stronger or weaker, depending on how you treat it.

Bones have three layers: the outer membrane, or periosteum, which supplies blood to the next layer; the hard, compact bone, which supports weight; and inside, the spongy bone marrow, which produces blood components, including blood cells and platelets. The 206 bones in the body are made up mainly of calcium. Besides producing blood cells and protecting some organs (as the skull and ribs do), bones are best known for enabling movement.

Many teens don't realize "that the skeleton is the framework that carries you around," says Dr. Laura Tosi, chief of pediatric orthopedic surgery at Children's National Medical Center in Washington, D.C. "If it's not in good shape, it's going to cost you your independence."

Tosi isn't just speaking about your independence now. Teen years are "the age of bone growth as well as mineralization--how hard and strong the bones get," says Dr. Anastasia Fischer, a at Children's Hospital in Columbus, Ohio. "It's very important that teenagers develop the strongest bones possible."

What's the rush? People have until roughly age 20 to maximize the growth and strength of their bones. After that age, bones gradually but steadily become weaker. So a healthy skeleton needs all the building and buttressing it can get during the critical teen years.

Tosi illustrates the situation this way: "I like to use the analogy of a sand castle when thinking about the skeletal system. If you build a puny one, it's going to get knocked over by the littlest wave. But if you build a big, strong one, it can hold up to so much more."

Build Your Bones

Strong bones are supportive bones, and they don't break easily. One of the most effective ways to build strong bones is exercising. But not just any exercise will do, cautions Tosi. "You need activities that involve impact loading on the bones," she says. Impact loading refers to any exercise in which a person supports his or her own body weight. Walking, running, jumping, and weight training all put stress on the bones and make them stronger.

How? Bones, like muscles, respond to use by directing new growth to areas that were recently used. In other words, lift weights or do other impact-loading activities and your bones get stronger. Aim for at least half an hour of impact-loading activities most days. Exercise increases not only bone density but also bone size. "If you look at kids who play racket sports, the bones in their serving arms are immensely bigger than [those] on the nonserving side," Tosi says. "Bone size is important." Similarly, bones that are as hefty and solid as they can be are less likely to fracture.

To Last a Lifetime

It might be hard to imagine that your choices today will affect you years from now. But think about older people you know who are stooped or frail and need help just to move around. When they were your age, they probably didn't do what they needed to maximize their bone health. And as Egan has learned, doing the right things for your bones means not just a better future but a more enjoyable present.

RELATED ARTICLE: Got calcium?

Calcium is one of the chief components of bones. Unfortunately, the body doesn't produce it, so you need to get it through your diet.

For teens, "the recommended amount of calcium is 1,200 to 1,500 milligrams a day," says Dr. Anastasia Fischer, "and should be split into at least three servings a day," with no more than 500 milligrams at once. That helps the body absorb calcium better.

It's best to get calcium from food rather than a pill. That way, your overall diet is more healthful. At right are some of the top sources of calcium. In addition, look for foods that are fortified with calcium, such as orange juice and cereals.

Source: USDA Nutrient Data Laboratory, 2002

Discuss

* What are the components of bone and what do they do? (The periosteum supplies blood; the compact bone supports weight; and the marrow produces blood cells and platelets.)

* What is impact loading? (doing exercises in which a person's bones support his or her body weight)

* Why are the teen years significant for bone health? (Bone growth and bone health peak at about age 20.)

Do

To help your students understand the risks inherent in poor bone development, have them research the causes, costs, effects, and treatments of osteoporosis. Then challenge students to write a persuasive letter to the school or local newspaper urging teens to take better care of their bones, including reasons why doing so is important.

Resources

This Web site explores bone health in depth, with many links and helpful tips: www.nysopep.org/page.cfm/105.

Ouch! When bones break, it's important to treat them properly. Get advice at www.kidshealth.org/teen/safety/ first_aid/broken_bones_sheet.html.

A teen-oriented, downloadable brochure with calcium facts and menu ideas is available at www.nichd.nih.gov/milk/kids/ milkmatters.pdf.

Want tips on impact loading? Check out www.cdc.gov/powerfulbones/ stayingstrong/index.html.

Top Foods
For Calcium

Food                        Serving    Calcium
                              Size     [in mqi

Muenster cheese              1 oz.       203
Cheddar cheese               1 oz.       204
Collard greens, cooked       1 cup       226
Dried figs, uncooked         1 cup       287
Whole milk                   8 oz.       290
2% milk                      8 oz.       298
Skim milk                    8 oz.       301
Low-fat yogurt with fruit    8 oz.       338
Sardines, in oil,           3.75 oz.     351
including bones
Low-fat plain yogurt         8 oz.       448
Nonfat plain yogurt          8 oz.       488

oz. = ounces; mg = milligrams