For many parents, the years between 9 and 14 are particularly difficult ages for rearing children. Puberty poses a lot of challenges, but one most people don’t consider is that it defines the narrow window in which humans build the bulk of their skeletons.
A story on NPR recently explained that a lot of kids that age aren’t getting what they need to build strong bones. And it’s not just a matter of nutrition, of sufficient amounts of calcium and vitamin D. They are essential for bone health, but so is physical stress.
In short, kids need to run and jump and make their bones work.
One of NPR’s sources, an orthopedic surgeon, said that when children jumped up and down between classes, for a total of about 15 minutes a day, they added mass to their leg bones.
For bones, bigger is better — the bigger they are, the harder they are to break.
"We think the bounce probably sends an electrical or other signal right up the skeleton, saying, 'OK, time to give more, time to build more bone.' " the doctor told NPR.
Any impact activity is good — jogging, tennis, basketball, dancing… Whatever your kid is happy doing. Federal health officials say that kids should get at least one hour of exercise every day, but it doesn’t have to be all at once. And it’s most important to get during the bone-building window.
On the nutrition front, children of all ages, including teenagers, often have a diet with too little calcium and vitamin D to build the best bones.
Children from 9 to 18 should get 1,300 milligrams of calcium every day. That’s about four or five glasses of milk, or the equivalent.
Most teens don’t come close. Only about 15 in 100 high school students drink milk, and only about 9 in 100 girls do, often because they perceive it as fattening. But that's not true — one glass of skim milk contains no fat and approximately 80 calories, about the same caloric content as an apple.
Good sources of calcium other than milk are yogurt and cheese.
Vegetables can be a source of calcium, but you have to eat tons of them to get the recommended levels. A cup of broccoli, for example, has only 42 mg of calcium. But fortified orange juice, breakfast cereals and tofu are good sources.
It’s always better to get this mineral from food, not supplements, especially for kids. The body absorbs calcium better from food than it does from supplements.
Even if kids get sufficient calcium, it won’t make much difference if they’re not getting sufficient vitamin D, which enables calcium to be absorbed during digestion.
Children, and most adults, need 600 international units of vitamin D a day. It’s found in fatty fish (salmon and sardines), and like calcium, is added to milk and orange juice. And, of course, we absorb it through exposure to the sun.
Unlike calcium, vitamin D can be appropriate in supplement form for some teenagers, especially if they don’t drink milk or eat fish and other healthful foods. A reasonable supplement for them would be about 400 international units per day.