Physical training increases the number of red blood cells, the volume of blood plasma and can increase vascularity, which are normal physiological responses to training. Haemoglobin, the iron-containing protein in the red blood cells, transports oxygen from the lungs to the muscle cells, the site of substrate oxidation to energy. Iron is critical to the functional role of blood in oxygen transport and cellular oxidation reactions that occur in the mitochondria that generate ATP for muscle contraction.
Iron is a nutrient of concern in athletes of both sexes, but particularly female athletes. Other important micronutrients involved in blood health, in terms of the formation and function of red blood cells that may be of concern, are folate, vitamin B12 and the trace element copper. However, there are inadequate data on these nutrients to assess their significance in athletes. It is well established that requirements for iron are higher in athletes compared with untrained controls, although the data currently available are insufficient to allow any quantification of specific requirements for different groups of athletes. Severe deprivation of folate, vitamin B12 and iron results in anaemia and significantly reduces endurance performance capacity. Copper deficiency is rare.
Iron deficiency, both with or without anaemia, can impair muscle function and limit work capacity, depending on the severity of the depletion and is the main focus in this section.