The Oxygen-Nutrient Performance Relationship

There is no question that physical activity can alter blood-iron status and that blood-iron status can also alter physical activity performance. One study assessing 747 athletes and 104 untrained controls found that endurance athletes had lower hemoglobin and hematocrit levels than either power- or mixed-trained athletes, suggesting that the difference may be due to dilutional pseudoanemia and, perhaps, a greater degree of foot-strike hemolysis.⁶

Athletes with higher exercise durations and workloads also appear to store less iron (ferritin). These findings imply that athletes are indeed at higher risk of compromised iron status than are nonathletes, and higher exercise durations within the athlete pool create even greater iron-status risk. Endurance athletes who put in large numbers of training hours (and miles) are therefore at highest risk of poor iron status even though they rely most on aerobic metabolic processes to achieve their endurance.

Restrictive intakes, as are common among athletes involved in weight-classification or aesthetic sports, almost always supply inadequate levels of vitamins and minerals. There is real risk, therefore, that a significant proportion of the athlete population has less than optimal oxygen-utilization capacity-a fact that surely inhibits optimal performance. Iron deficiency, even without anemia, reduces muscle work potential, and iron-deficiency anemia makes matters worse because of a further reduction in oxygen-carrying capacity.

Iron-deficiency anemia is likely to be more prevalent among athletes (particularly female athletes) than among nonathlete groups.⁷ The effects include reduced athletic performance and impaired immune function. Young female athletes should consider either consuming more iron-rich foods (particularly red meats) or taking iron supplements under the supervision of a doctor.

Iron deficiency occurs in athletes for many reasons, including inadequate intake, hemolysis, and menstrual blood loss in females.⁸ However, the most common iron problem in athletes is caused not by blood loss but by an enlargement of the blood volume without a concomitant increase in the constituents of the blood, including red blood cells. This condition, referred to as sports anemia or dilutional pseudoanemia, is a normal state that occurs when athletes increase training intensity.

The underconsumption of other nutrients may also affect oxygen utilization. Magnesium deficiency increases oxygen requirements needed to perform submaximal exercise, thereby reducing endurance performance.⁹ Folate and vitamin B₁₂ deficiencies result in megaloblastic anemia, a condition that results in malformed red blood cells with a reduced life expectancy. This reduced functional duration makes it difficult for athletes to constantly manufacture red cells, which are also being destroyed through foot-strike hemolysis. The result is fewer cells that can carry oxygen and remove carbon dioxide, a sure formula for poor athletic performance.

Data from past studies indicate a higher prevalence of hematuria in athletes, with multiple causes that include the following:¹⁰

• Foot-strike hemolysis
• Renal ischemia
• Hypoxic kidney damage
• Release of a hemolyzing factor
• Bladder or kidney trauma
• Nonsteroidal anti-inflammatory drug intake
• Dehydration
• Increased circulation rate
• Myoglobinuria release
• Peroxidation of red blood cells

A chronic loss of red blood cells in the urine, a condition brought on by frequent high-intensity and long-duration practice sessions, would contribute to anemia, a problem that reduces competitiveness in any athlete. Athletes should be careful, therefore, to take in sufficient nutrients (particularly iron) to replace that which is lost. Luckily, the erythropoietic process (production of new red blood cells) appears to be remarkably resilient in the face of exercise stress; it is capable of producing a large and adequate number of red blood cells provided a sufficient nutrient base (in particular iron, folate, and vitamin B₁₂) is available.¹¹ Some athletes try to enhance erythropoiesis by taking erythropoietin (EPO), but this blood-doping technique is illegal and has the potential for increasing blood viscosity, with subsequent thrombosis and potentially fatal results.¹²

Dilutional pseudoanemia

When athletes begin an intensive exercise program, they experience a rise in both blood volume and red blood cells. However, because the blood volume increases at a faster rate than the red blood cells, it appears as if they have anemia. Since this condition is transient (eventually the concentration of red cells becomes normal), it is referred to as a dilutional pseudoanemia (also known as sports anemia or athletic anemia).

Foot-strike hemolysis

Repeated foot strike associated with running causes red blood cells to break down. Red cells circulating in capillaries through the bottom of the feet are crushed by the foot strike. The faster red blood cells break down from foot-strike hemolysis, the more difficult it is for athletes to maintain a normal concentration of red blood cells (their bodies can't make the red blood cells fast enough), which may result in anemia.