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The important role of physical activity in skeletal development: how exercise may counter low calcium intake.

Skeletal development requires reasonable intakes of all the nutrients required by bone tissue, but energy and protein are critical for attainment of growth commensurate with hereditary determinants. Although clearly important for skeletal development, the amounts of calcium needed for optimizing skeletal mass and size remain difficult to determine. Many children in both developed and developing nations gain near-optimal skeletal mass and size with low calcium intakes, without adverse effects. A currently missing determinant in most considerations of requirements by nutritionists is the lifestyle variable of physical activity. In this perspective, I attempt to incorporate the role of activity into the thinking about calcium requirements in the early stages of the life cycle, ie, the first 2 decades of life. Even though cells of soft tissues have essential needs for calcium ions to support life, the body’s clearly overwhelming quantitative need for calcium resides in its skeletal utilization, not in its soft tissue uses. A greater bone mass gained early in life is now considered a critical factor in protecting against osteoporotic fractures later in life. The critical years for skeletal growth and accumulation of bone mass lie in the prepubertal and pubertal decade beginning at <10 y in girls (1).