If there's a preteen girl in your life, you know these years are a time of tremendous intellectual, emotional and physical change. Most of the changes are obvious. Your daughter seems to add an inch overnight. She may be starting to menstruate. You help her buy her first bra. But there's one crucial area of growth you may not be aware of: her bones. Girls (and boys) reach most of what doctors call "peak bone mass"—the densest bones of their lives—in the years around puberty. In adulthood, they slowly lose bone, a process that accelerates rapidly at menopause. Men also lose bone mass as they age but the process is far more gradual. That's why women are more vulnerable to osteoporosis, a disorder characterized by fragile bones. It's a disease you should take seriously: more women die of complications from osteoporosis than breast cancer.
Although genetics play a role, a woman's risk of osteoporosis is also determined by her diet and the amount of weight-bearing exercise she gets during childhood and adolescence. Pediatric orthopedic surgeon Laura L. Tosi, director of the bone health program at Children's National Medical Center in Washington, often uses the metaphor of building a sandcastle to describe bone growth. "You build it and it gets bigger and bigger, but there's a point where you can't build any more," she says. That endpoint is sometime around puberty, although scientists aren't exactly sure when. (Some doctors think bones continue to grow a little more in late adolescence and early young adulthood.) Puberty generally comes earlier in girls than boys and that means girls have less time to build bone and are more vulnerable to the waves of aging that erode the sandcastle. "An extra inch or two on that sandcastle means you're going to endure a lot more waves," says Tosi.
Your bones are living tissue—just like skin. Not only do they keep you upright, they are also your body's storehouse for calcium and phosphorous. Bones grow in two ways: bone modeling (essentially new construction) and bone remodeling (renovation of existing bone). During childhood, both processes go on at once, although bone modeling dominates. After you reach peak bone mass, the two processes continue at roughly the same rate, remaking your entire skeleton about every 10 years. From about age 35 on, measurable bone loss starts as the remodeling begins to outpace new construction. That shift accelerates at menopause when women lose estrogen, the female sex hormone that slows remodeling.
That's if everything is working normally. But a lot can go wrong. Certain diseases in childhood predispose some to bone problems in later life. The age of the child determines whether there's time to fix the damage. Tosi says a child who survives leukemia as a young child, for example, still has time to make up the time missed in bone growth. But a girl who becomes anorexic or stops menstruating for other reasons in her early teens may never be able to recoup the bone she lost through lack of nutrition during that time. Other risk factors during childhood include long-term steroid use (often used to treat asthma, for example) and gastrointestinal disorders like Celiac disease that prevent absorption of nutrients.
It may seem excessive to worry about something that's not going to be a threat for half a century, but bone scientists say the consequences of ignoring the critical window of bone growth can be devastating. Half of all women over 50 will sustain an osteoporosis-related fracture in their lifetimes. As scary as that is, you can increase your daughter's chances of beating the odds by teaching good bone habits now. Getting that message across is the focus of a new public service educational campaign sponsored by the American Academy of Orthopedic Surgeons (AAOS) and the National Institute for Child Health and Human Development (NICHD). The campaign ads feature a young girl with the headline "Almost Past Her Prime." "This is a prevention campaign," says Dr. James H. Beaty, AAOS president and a pediatric orthopedic surgeon at the Campbell Clinic in Memphis. "We're trying to prevent future problems rather than treat them when the kids become adults."
Start with exercise. Too many girls aren't active enough, increasing their risk of becoming obese as well as getting brittle bones when they are older. In order to become strong, bones need weight-bearing activities like walking, running or bicycling. These spur bones to become denser. Tosi says dancing is a particularly good exercise for avoiding fractures because it also improves balance. Team sports such as basketball, volleyball and soccer are also fine ways to build bones. Swimming, on the other hand, is great for building muscle but doesn't help bones because it's not weight bearing.
Diet is the second key element. Bones need both calcium and vitamin D. Calcium is the building block of bones and vitamin D "lets the calcium in," says Tosi. The best source of calcium is food, especially dairy products, certain fish and green vegetables. The current recommendation is that 4- to 8-year-olds should get 800 milligrams of calcium daily and 9- to 18-year-olds should get 1,300 milligrams. Less is known about Vitamin D, but Beaty says 9- to 18-year-olds should get 400 International Units (IUs) a day. For more information on specific food sources of these two nutrients, see this link from the National Institutes of Health. This NIH site has more information on Vitamin D.
For more on children and bone development, The National Institute of Arthritis and Musculoskeletal Development offers a pamphlet that can be downloaded. The AAOS also has information in the patient education section of their Web site.