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When it comes to sports, performance is everything. But what happens when an athlete's ability to perform is hindered by a health condition like anemia? In some instances, sports can exacerbate or even cause anemia, a condition characterized by a reduction in hemoglobin and red blood cell levels in the blood. This is particularly common in endurance athletes and is often linked to iron deficiency.
Iron is a vital component of hemoglobin and myoglobin, both of which are essential for the transport of oxygen in the blood. It also plays a crucial role in energy production and is a part of many enzymes. The recommended daily intake of iron is between 12-16 mg, but this can vary based on individual factors such as age, sex, and physical condition.
Iron is absorbed in the intestines, specifically the duodenum and jejunum. The absorption process is influenced by several factors, including stomach acid production and the health of the intestinal mucosa. A well-balanced diet typically provides about 6-7 mg of iron per 1000 kcal.
Iron in our diet comes in two forms: heme and non-heme. Heme iron, which is found in animal-based foods, is absorbed at a much higher rate (over 20%) than non-heme iron (less than 5%). Non-heme iron is more common in plant-based foods. Certain factors can affect the absorption of iron. For instance, oxalic acid and phytic acid can reduce iron absorption, while vitamin C can enhance the bioavailability of non-heme iron.
Iron is stored primarily in the liver as ferritin. The total amount of iron in the human body is approximately 4-5 g.
In endurance athletes, such as cross-country skiers, iron loss can be significantly higher than in sedentary individuals. This can be attributed to several factors:
In sedentary individuals, gastrointestinal losses account for about 60% of the total iron loss (excluding menstrual losses). This is primarily due to minor blood losses and the breakdown of red blood cells. However, after prolonged running events, over 80% of participants experience gastrointestinal bleeding, which can result in iron losses of between 0.7 and 0.9 mg.
While urinary iron losses are typically minimal in sedentary individuals (0.1mg/day), they can increase significantly in endurance athletes.
Sweating can lead to increased shedding of epithelial cells, which can contribute to minor iron losses, even in endurance athletes.
Women of childbearing age lose between 30 and 60 ml of blood each month due to menstruation. This can result in a loss of around 1.0 mg of iron per day or 30 mg per month. In female athletes, these losses can be compounded by urinary and gastrointestinal losses and dietary restrictions.
Endurance runners often experience increased red blood cell breakdown due to capillary damage in the feet. The extent of this phenomenon is not entirely understood but could explain why runners are particularly susceptible to iron deficiency anemia.
Iron deficiencies can lead to a decrease in the concentration of hemoglobin in the blood, which in turn can impact an athlete's performance. Initial symptoms of iron deficiency include a general reduction in strength, followed by progressive decreases in power and aerobic endurance. This is particularly noticeable in middle-distance and cross-country athletes.
For this reason, some suggest that endurance athletes should increase their iron intake to around 20 mg/day. However, it is crucial to avoid excessive iron intake as it can be toxic and dangerous in chronic conditions.
If an athlete's serum iron, ferritin, and transferrin levels are within normal ranges, taking iron supplements to correct even mild anemia is unnecessary. A reduction in hemoglobin and hematocrit levels is more common in athletes participating in endurance sports. The exact reason for this is not entirely understood.
However, it's clear that a decrease in hemoglobin and hematocrit levels can negatively impact performance by limiting the availability of oxygen. On the other hand, an increase in plasma volume, common in endurance athletes, can make the blood more fluid, increasing the systolic volume and blood flow to the tissues.
It's important to note that in cases of hypervolemia, the hematocrit level decreases because the blood is more diluted, but the quantities of red blood cells and hemoglobin remain the same.
In conclusion, understanding the role of iron in the body and how it can be affected by physical activity is crucial for athletes. Iron deficiency can significantly impact athletic performance, making it all the more important to monitor and maintain healthy iron levels.