Age Changes in Body Composition
Even though the water content of the lean body mass in adults is very constant at 75% that of newborn infants and fetuses is somewhat greater. Indeed there is a “drying out” of the body age, as well as change in the intra and extra cellular distribution of water.
The overall fat concentration of the body increases during gestation until birth, and the water content declines from birth to adulthood. If the infant is premature, there is an additional loss of water with age related to the change in fat content. Although the water content declines, the nitrogen content increases, reflecting a higher protein concentration in adult tissues as compared with that of the newborn infant or fetus. The changes from a greater to a lesser extracellular fluid volume with growth and development are reflected in the decreased sodium concentration of body tissue with age and increase in potassium concentrations. The overall contributions of calcium, magnesium and phosphorus, most of which are present in the bone, also increase dramatically from birth to adulthood, coinciding with the process of body “mineralization”.
While the proportion of the body water in the central nervous system, skin and subcutaneous tissue decline that most other organs increase, especially in the muscles. Perhaps more of the organ systems including muscle and parenchymal tissues, increase their proportion of intracellular water, where as the opposite is true of the skin and subcutaneous tissue.
These trends continue during aging. Western adult slowly losses lean body mass and accumulates more fat onward from early adulthood. The loss of lean body mass is more evident in men than women until after menopause, when it accelerates. This change is ascribable mainly to loss of cellular versus extracellular mass, reflected in losses of potassium and nitrogen that average 22.5% and 17.5%, respectively from 25 to 75 (for both sexes).
Age Changes in Body Composition
