Teens may not think much about what they eat. Or how what they eat today will affect them tomorrow, or twenty years from now. But over the last several decades, researchers from the National Institute of Child Health and Human Development (NICHD) have learned a great deal about how a nutritionally balanced diet during childhood and adolescence works to prevent the onset of damaging adult diseases.
One long-lasting effect of nutritional imbalance during adolescence is osteoporosis, a bone-crippling disease characterized by low bone mass and an increased bone fragility. Once recognized primarily as an elderly woman's disease, osteoporosis is now being acknowledged as a partially preventable "adolescent" disease because the occurrence of osteoporosis is influenced by bone mass attained during the first three decades of life, as well as the amount of bone lost after menopause. An optimal calcium intake during adolescence, when 50 percent of adult skeletal mass is formed, decreases the risk of the crippling fractures caused by osteoporosis.
Attaining genetically determined peak bone mass is, truly, "kid-stuff," and a bit more. A recent NICHD-supported study found that calcium supplementation of the diets of girls, ages 12 to 16, produced a 14 percent increase in bone density in comparison to unsupplemented girls. Though seemingly minimal, the impact of this 14 percent increase in bone density is striking: for every 5 percent increase in bone density, the risk of fracture declines by 40 percent. And, by the time adolescents finish their "growth spurt" around the age of 17, approximately 90 percent of their adult bone mass will have been established.
But a recent national survey indicates that 85 percent of adolescent females do not consume the Recommended Daily Allowance (RDA) for calcium. Many adolescent females avoid dairy products, the best source of calcium, because of the perception that all dairy products are fat-laden foods. Other teens replace milk with regular or diet soda, unconcerned about the "empty calories" or limited nutritional value of soda. Some teens are not aware of the serious, long-lasting implications of inadequate calcium consumption. And most do not think they will ever become one of the 26 million women that suffer from osteoporosis today. NICHD is working to ensure that teens can avoid this bone-crippling disease by conducting research on the teen calcium crisis and developing a public health campaign to get female teens out of their calcium conundrum.The Recommended Daily Allowance of Calcium
In 1994, NIH, including NICHD and other institutes with the Office of Medical Applications of Research (OMAR), sponsored a Consensus Development Conference on Optimal Calcium Intake. The conference report recommended that young adult women, up to age 24, ingest 1,200-1,500 mg of calcium per day, slightly above the current RDA for female adolescents. The current RDA for adolescent females, 1,200 mg per day, was last calculated by the National Research Council's RDA Subcommittee in 1989. The RDA Subcommittee set the 1,200 mg per day RDA by extrapolating data from adult, not child-based, calcium studies, because so few studies of child calcium requirements had been conducted. The RDA Subcommittee is reviewing and updating the RDA for several vitamins and minerals, including calcium, and will now have available data from several large-scale studies of calcium requirements in children. One of these studies was conducted by NICHD-funded researcher Thomas Lloyd, Ph.D.Nutrition Research at NICHD: Female Adolescents and the Calcium Crisis
At Pennsylvania State University, Lloyd studies the dietary, endocrine, and lifestyle factors that affect the acquisition of peak bone mass in female adolescents. Based on the results of recent placebo-controlled calcium supplementation studies, Lloyd found that calcium-supplementing the diets of girls ages 12 to 16 produced a 14 percent increase in bone density in comparison to unsupplemented girls. Lloyd also found that calcium-supplementing the diets of girls ages 14-16 produced more than twice the increment in bone density as those supplemented at ages 12-14, identifying the ages of 14-16 as a time of special concern for adding to bone density.Calcium Requirements During Adolescent Pregnancies
Currently, there is no established Recommended Daily Allowance for calcium intake for pregnant adolescents. Logically, adolescents who become pregnant, nearly one million each year, need more calcium to maintain a positive balance for both themselves and their fetus. NICHD-funded researcher Jorge Prada, M.D., is evaluating the calcium requirement for pregnant adolescents, the role that calcium plays in bone metabolism, the incidence of hypertension, and the occurrence of pre-eclampsia, which is the development of dangerously high hypertension during pregnancy. Prada is currently recruiting pregnant adolescents between the ages of 12-20 to participate in the Randomized Calcium Trial in High Risk Pregnancies at the University of Cincinnati. His trial is the first U.S. study to address the calcium requirement of the pregnant adolescent.The Adolescent Female Athlete: Disordered Eating, Amenorrhea, and Osteoporosis
The competitive adolescent female athlete may often be at risk for developing this trio of medical disorders. The compounded effects of osteopenia (reduced bone mass), amenorrhea (loss of periods), and disordered eating can be debilitating for the female teen athlete. In fact, recent studies have shown that the spinal density of some young female athletes is similar to that of women in their 70s and 80s. Despite the fact that their weight-bearing exercise acts to increase bone density, this exercise often cannot compensate for the lower estrogen levels associated with menstrual dysfunction and the resultant loss of bone. NICHD-funded researcher Michelle Warren, M.D., medical director for the Women's Center for Health and Social Issues at St. Luke's-Roosevelt Hospital, studied the eating patterns of ballet dancers to determine if dietary patterns could account for the incidence of stress fractures. Warren found that stress fractures were significantly associated with a more restrictive diet. The majority of the dancers with recent stress fractures had weights 75 percent of their ideal weight, exhibited a high incidence of eating disorders, and had a low dietary fat intake. And, while many young female athletes may aspire to be "ultra-thin," the loss of 25 percent of total body weight causes serious physiological disturbances, like amenorrhea, which has been linked to increased stress fractures.Public Health Implications of the Declining Calcium Intake in Female Adolescents
Though the threat of osteoporosis may be in the far-off future for many female teens, NICHD recognizes the immediate need to reverse their inadequate calcium intake. NICHD is planning a public health campaign geared toward increasing their calcium consumption by encouraging them to consume nature's most calcium-rich food: milk.
The campaign will concentrate first on increasing the calcium intake of the most milk-averse teens, females ages 11-17, and then on younger girls, ages 6-11. The goal of the NICHD-proposed campaign is to increase the consumption of milk so that most female adolescents consume 1,200-1,500 mg of calcium per day, equivalent to approximately 4-5 eight-ounce glasses of milk. The NICHD campaign will educate parents and physicians about the importance of including the appropriate amount of calcium in the daily diets of young children and adolescents, and emphasize that milk consumption is a must during the childhood years.
An additional component of the campaign will be educating the nearly two million adolescent female athletes participating in interscholastic competition about the importance of an appropriate calcium intake. Because many female athletes are overtly "fat conscious," dairy products, often perceived as only fatty foods, are avoided. The campaign will seek to educate them on the effects of a dangerously low calcium intake, including the predisposition to stress fractures as teen athletes and the eventual onset of osteoporosis, and the availability of low-fat milk. The campaign will also concentrate on teaching the female adolescents who become pregnant each year about the greater need for calcium during pregnancy.
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