Experts believe calcium should come from food sources whenever possible. However, if you think your children are not getting adequate calcium from their diet, you may want to consider a calcium supplement. For optimal absorption, no more than 500 mg of calcium should be taken at one time.

How does physical activity help my kids' bones?

Muscles get stronger when we use them. The same idea applies to bones: the more work they do, the stronger they get. Any kind of physical exercise is great for your kids, but the best ones for their bones are weight-bearing activities like walking, running, hiking, dancing, tennis, basketball, gymnastics, and soccer. (Children who tend to play outside will also have higher vitamin D levels.) Swimming and bicycling promote your kids' general health, but are not weight-bearing exercises and will not help build bone density. Organized sports can be fun and build confidence, but they are not the only way to build healthy bones.

The most important thing is for your kids to spend less time sitting and more time on their feet and moving. Alone or with friends, at home or at the park--one of the best gifts you can give your kids is a lifelong love of physical activity.

Is it possible to get too much exercise?

For most people, including children and teens, the challenge is to get enough physical activity. However, excessive exercise and overtraining, often coupled with restrictive eating, can be a problem, especially for some female athletes and dancers, as well as girls who become obsessive about weight loss. Overtraining, like eating disorders, can result in decreased estrogen and eventually lead to thin bones that break easily.

Years ago, it was not unusual for coaches and trainers to encourage athletes to be as thin as possible for many sports, including dancing, gymnastics, figure skating, running, and diving. Fortunately, many coaches now realize that being too thin is unhealthy and can negatively affect performance as well as lifelong health.

So, my kids need to eat foods that are rich in calcium and get plenty of weight-bearing exercise. Is there anything else they can do to keep their bones healthy?

Yes. They should avoid smoking. You probably know that smoking is bad for the heart and lungs, but you may not know that it's harmful to bone tissue. Tobacco, nicotine, and other chemicals found in cigarettes may be directly toxic to bone, or they may inhibit absorption of calcium and other nutrients needed for bone health. The many dangers associated with smoking make it a habit to be avoided.

You may think it's too early to worry about smoking, but the habit typically starts during childhood. In fact, most people who use tobacco products start before they finish high school. The good news? If your kids finish high school as nonsmokers, they will probably stay that way for life.

Children who learn good eating and exercise habits by their preteen years are more likely to carry these habits with them for the rest of their lives.

My son has asthma and takes a steroid medication to control it. His doctor said this might affect his bones. Is there anything we can do about this?

Asthma itself does not pose a threat to bone health, but some medications used to treat the disease--when taken for a long time--can have a negative effect on bones. Corticosteroids, a type of anti-inflammatory medication, are often prescribed for asthma. These medications can decrease calcium absorbed from food, increase calcium loss from the kidneys, and shrink a child's bone bank account.

Kids with asthma need to take special care of their bones, making sure to get enough calcium and weight-bearing exercise. Some health care providers recommend extra calcium each day: between 1,000 and 1,500 mg. Many people think milk and dairy products--great sources of calcium and vitamin D--trigger asthma attacks, but this is probably true only if your child is allergic to dairy foods. Unfortunately, this misconception often results in an unnecessary avoidance of dairy products, which is especially risky for kids with asthma, who need extra calcium during their bone-building years.

Since exercise can often trigger an asthma attack, many people with asthma avoid weight-bearing physical activities that strengthen bone. Kids with asthma may be able to exercise more comfortably in an air-conditioned place, such as a school gym or health club.

Talk to your child's doctor for more information about protecting his bones while he is taking asthma medications.

My 8-year-old son is a daredevil and has already broken several bones. Could he have a problem like osteoporosis at this young age?

Osteoporosis is rare among children and adolescents. When it occurs, it is usually caused by an underlying medical disorder or by medications used to treat such disorders. This is called secondary osteoporosis. It may also be the result of a genetic disorder such as osteogenesis imperfecta, in which bones break easily from little or no apparent cause. Sometimes there is no identifiable cause of juvenile osteoporosis. This is known as idiopathic juvenile osteoporosis. Two or more low-impact fractures may be a sign of one of these disorders.

If you are concerned about your son's frequent fractures, talk to his doctor for more information.

You are absolutely right. Research has shown that children and adolescents do not tend to think much about their health. Their decisions about diet and exercise, for example, are rarely made based on "what's good for them." But we also know that you have a much greater influence on your kids' decisions and behaviors than you may believe. For example, many teenagers, when asked who has been the greatest influence in their life, name parents before friends, siblings, grandparents, and romantic partners.

The best way to help your kids develop healthy habits for life is to be a good role model yourself. Research suggests that active children have active parents. If you make physical activity a priority and try hard to maintain a healthy diet, including plenty of calcium, chances are your positive lifestyle will "rub off" on them along the way. Here are some things you can do.

• Be a role model. Drink milk with meals, eat calcium-rich snacks, and get plenty of weight-bearing exercise. Don't smoke.
• Incorporate calcium-rich foods into family meals.
• Serve fat-free or low-fat milk with meals and snacks.
• Stock up on calcium-rich snacks that are easy for hungry children to find, such as
  • Cheese cubes and string cheese
  • Calcium-fortified orange juice
  • Single-serving puddings
  • Individual cheese pizzas
  • Yogurt and frozen yogurt
  • Tortillas
  • Cereal with low-fat milk
  • Almonds
  • Broccoli with yogurt dip
• Limit access to soft drinks and other snacks that don't provide calcium by not keeping them in the house.
• Help your kids to find a variety of physical activities or sports they enjoy participating in.
• Establish a firm time limit for sedentary activities such as TV, computers, and video games.
• Teach your kids to never start smoking, as it is highly addictive and toxic.
• Look for signs of eating disorders and overtraining, especially in preteen and teenaged girls, and address these problems right away.
• Talk to your children's pediatrician about their bone health. If your child has a special medical condition that may interfere with bone mass development, ask the doctor for ways to minimize the problem and protect your child's bone health.
• Talk to your children about their bone health, and let them know it is a priority for you. Your kids may not think much about health, but they are probably attracted to such health benefits as energy, confidence, good looks, and strength.