Kids, Bones, and Stress Fractures
Stress fractures are fractures of the bones that occur from repeated submaximal loading. They are also called fatigue or insufficiency fractures, bone contusions, or stress injuries and they occur in adolescents more than ever. In part, this is because young people have increased their participation in and their intensity level of impact sports. Additionally, we are now better at diagnosing stress fractures using highly accurate MRI exams for people with unexplained pain. MRI testing, unlike x-rays, reveals the interior of bones and the increased reaction that occurs when bones are injured.
Prevention of stress fractures is targeted in two areas: nutrition and physical activity. To maximize peak bone mass, children must consume a minimum of 1000 mg of calcium per day (preferably 1500 mg). Calcium-rich foods include milk, cheese, yogurt, almonds, and spinach. Physical activity helps build bone mass, but sudden increases in the intensity, duration, or frequency of training can actually induce stress fractures. Sports participation in adolescents greater than 16 hours per week is associated with a higher incidence of fractures. To avoid stress fractures and other such bone injuries caused by overuse, we encourage kids to modify sports impact levels, wear athletic shoes with excellent shock absorption, run on shock absorbing surfaces, and maintain consistent exercise patterns and fitness levels.
Some Bone Mass Facts:
- With good nutrition and exercise, bone mass increases through childhood and plateaus between the ages of 20 and 30. The majority of bone mass is accumulated before the age of 15. Significant deficits are often realized around the age of 50, when the rate of bone mass loss exceeds the rate of bone mass accumulation.
- 20 – 40% of bone mass can be influenced by calcium intake, physical activity, hormones, and body mass.
- 60 – 80% of bone mass may be genetically determined.
Thin, premenstrual or ammenorheic, hyper-athletic girls with low calcium intake are obvious candidates for stress fractures. Menstrual irregularities reflect low serum estrogen levels. Estrogen is a key hormone in bone deposition and maintenance. Only upon the onset of menstruation does significant mineral get deposited to form more bone.
- Normal appearing boys and girls who do not consume adequate calcium may not develop stress fractures, but are decreasing their calcium deposits to the body’s bone bank, and are thus at higher risk for developing osteoporosis later in life.
- Direct sunlight is required to convert the passive form of vitamin D to the active form required for calcium utilization by bone.
The message is clear: At least 1500 mg of calcium, 400 IU of vitamin D, 30 minutes of direct sunshine without sunscreen, and 60 minutes of daily weight-bearing and resistance exercise is recommended to build bone mass and decrease fracture risk. The young increase bone mass; adults can prevent loss. Feed your children milk and other calcium and vitamin D rich foods, and encourage daily exercise and a significant amount of sunlight exposure. For children of all ages, treat yourself the same way.
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