When we think of osteoporosis, it is a vision of a stooped, elderly woman that tends to come to mind. It’s time to revise that vision. What we have learned through the years is that the foundation of bone strength is laid during adolescence, which means that adolescence is the critical time to act to prevent the development of osteoporosis later in life. Starting at age 8-9, bone mass begins to increase significantly, increasing most rapidly during puberty, with bone mass reaching its peak by approximately age 30. After age 30, bone mass slowly begins to decline. Osteoporosis affects approximately 55% of Americans over the age of 50, with 80% being women.
There are numerous factors that can influence peak bone mass. Genetic factors certainly play a role, so if there is a family history of osteoporosis or tendency toward bone fractures, it is even more important to be sure that all potential environmental factors are optimized. Environmental factors include the following:
1. Calcium intake — Adequate calcium intake between ages 9 and 18 is defined as 1200 to 1500mg per day. The upper tolerable limit for calcium is defined as 3000mg/day. Most of the calcium needs of children and adolescents are best met by milk and dairy products. While many vegetables contain calcium, the calcium density is low, making it much more difficult to achieve adequate calcium levels via vegetable intake as compared to dairy intake (vegetable intake remains extremely important for other health benefits, of course!). Numerous calcium-fortified foods are also available, including soy milk, soy yogurt, soy cheese, tofu, cereals, breakfast bars, and juices. Calcium bioavailability from these sources is thought to be equivalent to that of milk, except for soy milk, which has a bioavailability of approximately 75%. Children with lactose intolerance can drink lactose-free milk, which is equivalent in calcium content and bioavailability to regular milk. It is also important to note that low fat milks (skim, 1%, 2%), which are standard recommendations for children over age 2, have similar calcium content to whole milk.
For children and adolescents who do not achieve adequate calcium intake through diet alone, calcium supplements should be used. I tend to recommend Citracal, as calcium citrate has been shown to be more bioavailable than calcium carbonate in adult studies (similar studies involving children and adolescents are not available). Be sure to read the label carefully for whatever supplement you choose. For many supplements, more than one tablet must be taken to reach the advertised dosage.
2. Vitamin D intake — Vitamin D is crucial for enhancing calcium absorption from the intestinal tract. Adequate vitamin D dietary intake for children and adolescents is defined as 600 units per day, although the definition of adequate varies somewhat with degree of sunlight exposure (i.e. geographic location, season, use of sunscreens, dark vs. light skin pigmentation). Vitamin D is included in fortified milks and in most calcium supplements. Vitamin D can also be taken as a separate supplement, with vitamin D3 (cholecalciferol) being the formulation which is best absorbed. It is pertinent to note that vitamin D deficiency is something we are seeing commonly in adolescent girls, and as a result, I tend to recommend a higher vitamin D intake of 800-2000 units per day.
3. Exercise — Regular weight-bearing exercise during adolescence is at least as important as calcium intake, and perhaps even more important, in long-term bone mineralization. However, excessive exercise leading to interruption of menstrual function in females has a significantly detrimental effect, so the level of exercise must be monitored.
4. Cigarette smoking — Cigarette use results in decreased bone mineral density and should be avoided (for this and many other reasons!).
5. Carbonated beverages — Intake of carbonated beverages, especially colas, may lead to an increase in risk for fractures.
6. Anorexia nervosa — Extreme weight loss and underweight body habitus are strongly associated with decreased bone density. Any suspicion of an eating disorder should be investigated promptly.
One last thing I will mention is that it is somewhat confusing to determine the calcium content of foods from reading nutrition labels. Labels typically indicate calcium content as a percentage of the “daily value.” This “daily value” is set at 1000mg/day, which is less than the 1200-1500mg/day that is recommended for adolescents. I have attached a Calcium Chart that shows the approximate calcium content for some common foods.
Now, go tell your children to drink their milk — doctor’s orders!
Michelle Bennett, MD
Pediatric & Adolescent Associates, PSC