Sarcopenia

The etiology of sarcopenia remains unclear, but there are many possible factors involved (see Roubenoff and Hughes, 2000, for a detailed review). These include: (1) loss of alpha motor neurons in the central nervous system with age; (2) change in hormonal milieu in favor of a more catabolic muscle profile, with reductions in growth hormone, testosterone, and estrogen; (3) increased production of catabolic cytokines, especially interleukin-6 and possibly interleukin-1 beta and tumor necrosis factor-alpha, which favor muscle protein breakdown; (4) reduced physical activity, which leads to increased fat accumulation and possibly to resistance to the anabolic effects of insulin, perhaps due to increased tumor necrosis factor production by fat cells; and (5) reduced dietary intake of protein and energy.