Bone strength and the adolescent.

The strength of adult bone reflects factors that regulate bone quality (architecture) and density (bone mass or quantity of calcium deposited/unit of bone) acquired during childhood and adolescence. Near-maximal or peak bone mass of the vertebrae and femurs is achieved at the completion of pubertal development. Because inexorable loss of bone mass begins in mid-adulthood in normal people, the magnitude of peak bone mass determines individual risk for later development of osteopenia and osteoporosis--disorders of compromised bone strength that lead to bone fragility and increased fracture risk. Osteoporosis is a disabling and costly disease with a high mortality rate; one in five patients with an osteoporotic fracture dies within 1 year of sustaining the fracture. Fifty percent of maximal peak bone mass is accumulated during puberty in normal people who have adequate intake of calcium (1300 mg/day), vitamin D (400 U/day), and other macro- and micro-nutrients but avoid excessive weight gain, undertake appropriate weight-bearing exercises (walking, jumping, hopping), secrete normal amounts of sex hormones (androgen and estrogen) and growth hormone, limit ingestion of cola beverages, and avoid alcohol intake and smoking. This chapter reviews the regulation of bone development in adolescents and the factors that positively or adversely affect this process.