Oxygen Delivery and Cellular Utilization

Several elements, vitamins, and protein carriers provide, as a major function, the delivery and cellular utilization of oxygen. These elements work in unison to capture oxygen from the environment, transport oxygen through the blood to cells for metabolic actions, and remove the by-products (including carbon dioxide) of the oxygen-related metabolic activities.

Iron Iron is a critical element in the delivery of oxygen to working tissues. It is part of red blood cell hemoglobin, muscle myoglobin, and enzymes involved in electron transfer for energy metabolism. The body uses a priority-based system for iron, with hemoglobin at the top of the priority system. If stores of iron become sufficiently low to cause hemoglobin to drop, iron in myoglobin and iron-containing enzymes are scavenged so as to maintain red blood cell hemoglobin. Because of this, it is possible for an athlete to experience a reduction in performance even if hemoglobin and hematocrit (the two most common measures of iron status) appear to be in the normal range. It is important, therefore, that ferritin (stored iron) also be measured as a normal component of a blood test intended to screen for iron status (see table 7.1).

A typical iron-deficiency anemia is referred to as microcytic (small cell), hypochromic (dark in color). It is characterized by an inadequate number of red blood cells and existing cells that are smaller than normal due to low hemoglobin levels.

Transferrin Transferrin is a blood protein that carries iron through the blood to the bone marrow, spleen, and liver for either the storage of iron as ferritin or the manufacture of new red blood cells. It is a protein with a relatively short half-life that can be a marker for recent protein status, and it is used for this purpose. Low blood transferrin may be an indicator of protein or calorie malnutrition, resulting in inadequate synthesis of transferrin by the liver, or it can result from excess protein loss through the kidneys (proteinuria). A systemic infection or cancer can also lower the blood transferrin level. A high blood transferrin is a marker of iron deficiency. If an athlete has a low blood transferrin level, the production of hemoglobin can be impaired and can lead to anemia, even if there is ample iron in the body.

Ceruloplasmin Ceruloplasmin is a copper-containing protein involved in handing over iron from transferrin to hemoglobin in the formation of new red blood cells, or in removing iron from old red blood cells for inclusion in new ones. A copper deficiency results in low ceruloplasmin and can result in anemia that presents much like iron-deficiency (microcytic, hypochromic) anemia, possibly leading to a misdiagnosis. A ceruloplasmin deficiency is associated with iron accumulation in the pancreas, liver, and brain, resulting in neurological disorders.

Vitamin B₁₂ Vitamin B12 is a cobalt-containing vitamin that is also referred to as cobalamin. Two of its primary functions are the formation of red blood cells and the preservation of a healthy nervous system. The absence of vitamin B₁₂ when red blood cells are being formed results in cells that have a weak membrane. These cells, called megaloblasts, are fragile and live half as long as a normal red blood cell (60 days versus 120 days). The shortened life of these cells requires a constantly faster production of red cells to maintain normal oxygen-carrying capacity. However, this fast level of red cell production cannot be maintained, resulting in anemia. The anemia resulting from vitamin B₁₂ deficiency is referred to as pernicious anemia because it develops slowly over several years. Pernicious anemia is a megaloblastic, hypo chromic anemia, meaning that the red blood cells are large and misshapen and are low in color (the hemoglobin is spread out over a larger cell area, diluting the color.) Besides the reduced oxygen-carrying capacity from the anemia, pernicious anemia is associated with neurological symptoms and nerve degeneration. A small amount of vitamin B₁₂ is needed (the amount in one egg is likely to be sufficient for more than a month), but since it comes almost exclusively from meat sources, vegetarian athletes are at risk.

Folic Acid Folic acid, vitamin B₁₂, and vitamin C are all involved in protein metabolism. In conjunction with vitamin B₁₂, folate is needed for the production of red blood cells. Folate is also involved in nerve tissue development and is known to eliminate neural tube defects in newborns. The anemia associated with inadequate folate is similar to that produced by a deficiency of vitamin B₁₂ (megaloblastic, hypochromic anemia), and the reduced oxygen-carrying capacity that results is equally severe. However, while vitamin B₁₂ is obtained from animal sources, folic acid is best obtained from fresh fruits, fresh vegetables, and legumes.