Females require a significantly higher intake of iron than males, with the recommended daily allowance (RDA) in adult females being 18 milligrams (mg) per day, whereas males require only eight. Females need more iron than males to make up for the amount that is lost during menstruation; females can lose anywhere from one to five mg of iron per cycle. The RDA increases for females at 14 years of age (around menarche, the first occurrence of menstruation) and remains increased compared to that of males until menopause years.1
Unique Iron Needs for Female Athletes
Female athletes are particularly at risk for iron deficiency. One study reported that approximately 2.2 percent of female student-athletes have iron deficiency anemia, and 30.9 percent have iron deficiency without anemia. This is compared to 1.2 percent of male student athletes having iron deficiency anemia and only 2.9 percent having iron deficiency without anemia.2 Iron deficiency anemia is diagnosed when hemoglobin levels fall below a certain cut-off value. However, symptoms of iron deficiency, such as fatigue, can present without having low hemoglobin levels. Iron deficiency without anemia is diagnosed when ferritin levels are low or when transferrin saturation levels are low, but hemoglobin levels appear normal. Ferritin is the body’s main iron storage protein, and transferrin is the main iron protein transporter.
Female athletes most at risk for low iron intakes are those who are energy restricting and/or consuming a specialty diet that does not contain animal products (an important source of heme-iron), such as a vegan or vegetarian diet.3 Heme iron is found mainly in animal meats (red meat, poultry, and fish) derived from hemoglobin and myoglobin, and it is well absorbed by the human body. Non-heme iron, found primarily in plants (i.e., spinach and legumes) and fortified foods, is not as well absorbed by the body, with its absorption dependent on other nutrients or foods in a meal. For example, consuming non-heme iron with foods rich in vitamin C can increase its absorption.
Consuming a diet high in bioavailable sources of iron such as meat and seafood should be an area of focus for those at risk of iron deficiency.4 Supplementing with iron may be a consideration as well if adequate amounts are not able to be consumed through diet alone. Ferrous sulfate is the most commonly recommended form of iron supplement.5 However, low absorption may be an issue when supplementing with iron, and gastrointestinal (GI) side effects can be problematic.5,6 Dyspepsia, nausea, abdominal pain, and constipation/diarrhea are all possible side effects associated with supplemental iron intake.5 Recently, studies have shown that iron absorption from supplements may be greater when using alternate day supplementation methods, instead of consecutive day dosing.7
Factors Affecting Iron Status
There are a number of factors that may affect iron status in female athletes. There may be increased iron loss during exercise due to mechanical forces, causing exercise-induced hemolysis, the breakdown of red blood cells.4 Blood loss in the urine and GI tract may occur as well, especially in endurance runners.4,8 Exercise-induced inflammation may also impact iron status, resulting in increased levels of proinflammatory cytokines that stimulate the expression of hepcidin, a hormone regulator of iron transport and absorption.4,9 All these factors combined with the monthly loss of blood during female menstruation adds to the increased risk of iron deficiency in female athletes.
Excessive Iron Intake
While consuming enough iron in the diet and (sometimes) supplementation is important, excessive iron intake is also something to consider. Iron overload consisting of acute intake over 20 mg/kg may result in symptoms such as digestive upset and lightheadedness. Particularly excessive intakes can be more dangerous, leading to organ failure and death. The tolerable upper intake levels (ULs) for iron are set at 40 mg for both males and females from birth to age 14, 45 mg from age 14 and up, and 45 mg for pregnant or lactating females.
Considering these key factors when evaluating female athletes is important to properly care for the exercising female. Low energy availability, specialty diets that do not include highly absorbable sources of iron, and endurance athletes – especially runners – may be susceptible to iron deficiency. It may be important to assess not only hemoglobin levels, but ferritin levels as well as transferrin saturation levels, in these females at higher risk for deficiency.
