Q: My 15-year old daughter, who is a swimmer, dislikes drinking milk. She recently read in the paper that taking calcium and vitamin D supplements does not prevent osteoporosis later in life. Should I be concerned?
The issue of bone health has recently become front-page news in many major newspapers across the world. This is the result of a controversial publication presented in The New England Journal of Medicine about a month ago. The authors concluded that taking vitamin D and calcium supplements, in order to optimize bone health, made very little difference. In some patients, it actually increased the risk of developing kidney stones.
By coincidence, the American Academy of Pediatrics (AAP), concerned with poor calcium intake in children and youth, published their own recommendations regarding optimizing bone health (See: www.pediatrics.org/cgi/doi/10.1542/peds.2005-2822). In a very detailed position statement, the Academy lamented the fact that only 10% of girls between the ages of 12 and 19 years meet their daily calcium requirements; boys in the same age range do a little better as 30% meet their daily calcium requirements. The AAP states that inadequate calcium intake is a family issue. Maternal consumption of milk, for example, predicts the milk intake of young female children.
This recent controversy reminds me of two people trying to describe an elephant: one from the front and the other from the back. The perspectives vary greatly! The diary industry promotes their products and lobby the government; makers of supplements claim their product is absorbed the best; those who feel that diary products pose dangers use this dispute as an opportunity to promote nondairy foods; and trainers remind us that when it comes to building stronger bones, weight bearing activities are superior to swimming.
Calcium, genetics and physical activity all determine bone health. Yet at this point, the interaction of all three is not fully understood. It is, however, becoming increasingly clear that bone health later in life has a great deal to do with what happens during childhood, particularly during adolescence.
Approximately 40-50% of our total bone density is laid down during adolescence. If parents, doctors and patients do not pay proper attention to optimal calcium intake and lifestyle choices at this time, they may miss an important window of opportunity. According to Dr. Nancy Krebs, the immediate past chair of the Academy's committee on nutrition, it may be difficult to totally compensate for this missed opportunity later in life.
One of the methods to study bone density in children is known as dual-energy X-ray absorptiometry. It is, however, not a commonly performed test, and many detractors question the usefulness and reliability of this investigation.
It is impossible to recommend a single, adequate intake of calcium for all children. However, the National Academy of Sciences suggests the following intake per day:
- 0-6 months, 210 mg
- 7-12 months, 270 mg
- 1-3 years, 500 mg
- 4-8 years, 800 mg
- 9-18 years, 1300 mg
- 19-50 years, 1000 mg
- 50 - >70 years, 1200 mg
Another way to determine appropriate calcium intake is through a questionnaire devised by the AAP, and featured on the website of The American Diary Association (click on “calcium quiz” at www.3aday.org/3aDay/). The American Dairy Association is also leading an attempt to raise awareness of how increased diary consumption can help improve bone health.
For families who prefer nondairy products, the following foods may provide an option as a source of calcium:
- 3 ounces of Salmon, 203 mg
- ½ cup of tofu, 204 mg
- 1 cup of white beans, 161 mg
- 1 cup of broccoli, 62 mg
- 1 cup of collard greens, 266 mg
- 1 cup of baked beans, 127 mg
- 1 cup of canned or stewed tomatoes, 87 mg
The bioavailability (which refers to how easily a nutrient is recognized, absorbed and used by the body) of calcium in certain foods also needs to be considered. For example, the calcium provided in soy products has a low bioavailability. As for breast milk, the bioavailability of calcium is superb, especially when compared to infant formulas (58% and 38%, respectively). This explains why infant formulas have higher concentrations of calcium. In addition, the oxalate content (a salt compound which binds with calcium) in green vegetables determines how much calcium the body absorbs. For example, spinach, with its high oxalate content, provides less calcium than broccoli or collard greens.
A strong link has been found between poor bone health and obesity. This link may be related not only to a life of inactivity for some patients, but also to an excessive intake of soft drinks and fruit juices. Both of these products provide extra calories through heavy loads of sugar (At a recent Beaver gathering, I showed the boys and their parents how much sugar a can of soda contains. Their eyes almost popped out when I stopped at ten teaspoons of sugar!). In addition, the phosphates in soft drinks leach calcium out of bones.
In 1945, North Americans drank four times more milk than soft drinks, but by 1997 they drank nearly 2.5 times more soft drinks than milk. In some parts of the continent, teenagers get as much as 15% of their total daily calories from soft drinks.
In his book Eat, Play, and Be Healthy, Dr. W. Allan Walker, from Harvard Medical School, reminds readers that beverages are foods too. He also emphasizes that osteoporosis is a pediatric disease with geriatric consequences.
Dr. Ken Cooper, from the famed Cooper Aerobics Center in Dallas (www.cooperaerobics.com), recently commented that a heart attack has a fuse of 35 years and it is lit in childhood. The same may be said for the unfortunate middle-aged female who trips and breaks her hip, or who suffers through the agonies of backache brought on by weak bones. When it comes to optimal bone health, prevention is indeed better than the cure.
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An informed parent is ... an empowered parent.