Iron deficiency and reduced work capacity: A critical review of the research to determine a causal relationship

The causal relationship between iron deficiency and physical work capacity is evaluated through a systematic review of the research literature, includ ing animal and human studies. Iron deficiency was examined along a continuu m from severe iron-deficiency anemia (SIDA) to moderate iron-deficiency ane mia (MIDA) to iron deficiency without anemia (IDNA). Work capacity was asse ssed by aerobic capacity, endurance, energetic efficiency, voluntary activi ty and work productivity. The 29 research reports examined demonstrated a s trong causal effect of SIDA and MIDA on aerobic capacity in animals and hum ans. The presumed mechanism for this effect is the reduced oxygen transport associated with anemia; tissue iron deficiency may also play a role throug h reduced cellular oxidative capacity. Endurance capacity was also compromi sed in SIDA and MIDA, but the strong mediating effects of poor cellular oxi dative capacity observed in animals have not been demonstrated in humans. E nergetic efficiency was affected at all levels of iron deficiency in humans , in the laboratory and the field. The reduced work productivity observed i n field studies is likely due to anemia and reduced oxygen transport. The s ocial and economic consequences of iron-deficiency anemia (IDA) and IDNA ha ve yet to be elucidated. The biological mechanisms for the effect of IDA on work capacity are sufficiently strong to justify interventions to improve iron status as a means of enhancing human capital. This may also extend to the segment of the population experiencing IDNA in whom the effects on work capacity may be more subtle, but the number of individuals thus affected m ay be considerably more than those experiencing IDA.