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Iron in Health and Fitness

Denis Collier, RD, M.Sc., PFLC
COLLIER Fitness & Nutrition


Function

Iron is the component of hemoglobin that binds oxygen and allows it to be transported from the lungs to the muscles via the blood (1). Dietary Reference Intakes (DRI) suggests a requirement of 8 mg/day of iron for men, and 18 mg/day for females. Studies have shown that males regularly achieve their recommended intake, however females do not (2).

Food Sources

The iron in food is not well absorbed by the body. Iron comes in two types, heme and non-heme iron, with heme iron being absorbed the best. Heme iron exists in animal foods only; non-heme iron is found in both plant and animal foods (3).

The best sources of iron are beef, organ meats, clams and oysters. Dark poultry meat is also fairly high in iron. Legumes are another item from the meat and alternative group that are high in iron, but it is not in the heme form (3).

Dried fruits, baked potato, beets, spinach and broccoli have fair amounts of non-heme iron but it is not well absorbed. These foods also contain fibre and substances called oxalates which inhibit absorption (4).

Whole grain items contain the most iron of any food in the grain product group. Those marked with the words fortified or iron enriched are even better. However, this iron`s absorption is inhibited by the presence of fibre and substances called phytates in these foods (3).

Some substances, especially vitamin C and meat, are known to enhance the absorption of non-heme iron. Therefore, these items should be consumed along with sources of non-heme iron (4). Another way to obtain iron in the diet is through the use of cast-iron skillets in cooking. Iron can actually leech into foods left to simmer in such cookware (1).

Deficiency

Iron deficiency is one of the most common nutrient deficiencies in both the United States and the world (3,4, 5,6). The condition progresses through stages, the final of which is known as iron deficiency anemia. This condition is characterized by decreased hemoglobin levels attributable to decreased iron stores and includes symptoms such as paleness, tiredness, low vitality and inability to regulate body temperature in a cold environment (3,7). It has been reported that between 3-5% of the female population has iron deficiency anemia (3). Iron deficiency anemia is preceded by an earlier type of iron deficiency in which no anemia is present. This deficiency is accompanied by decreased levels of serum ferritin (a molecular indicator of iron storage), but little or no change in hemoglobin (3,7). In the U.S., the prevalence of iron deficiency without anemia in women 18-44 years old is 16% (8). Sports anemia is a term given to endurance athletes who have lower than normal hemoglobin levels, but normal levels of other iron status indicators. In fact, this is not a true anemia. The hemoglobin concentration is low due to the increase in blood volume that accompanies training. This may actually be beneficial to the athlete (3).

Iron in Fitness

Effects of Deficiency on Athletic Performance

There is little doubt that a reduction in hemoglobin concentration (i.e. iron deficiency anemia) has a detrimental effect on exercise performance (2,3, 4,9). Anemia impairs blood gas transport, thereby limiting work capacity (7). Most research to date has focused on the effects of anemia on function while little has been done on whether function is affected at the earlier stage of iron deficiency (9). One possible reason for this is that a standard cut-off value to diagnose low iron stores is controversial. Serum ferritin is used (often in conjunction with other indicators) but the range can be 12-20 ?g/L (5). The result is equivocal evidence. Some studies support an adverse effect of compromised iron status on aerobic capacity (VO2max), endurance and work performance in humans (5,9). For example, in a study by Zhu et al., an iron depleted group of women (with no anemia) had significantly lower VO2max scores than a group of women with normal iron status. The VO2max scores were significantly associated with serum ferritin levels, and not hemoglobin levels. The conclusion was that the lower VO2max in non-anemic women with iron depletion was likely caused by factors related to reduced body iron levels, but was unrelated to decreased oxygen carrying capacity of the blood.

However, many other studies have not found a decrease in athletic performance accompanying iron deficiency without anemia, nor have they found any benefits for iron deficient non-anemic athletes supplementing with iron beyond improving iron status. The effect of low serum ferritin (iron deficiency without anemia) on athletic performance remains controversial and needs further research to be conclusively determined (2,3, 4).

Iron Status of Athletes

Young women who exercise regularly (particularly runners) seem to have a high risk for iron deficiency (4,7, 8). Estimates of non-anemic iron depletion among female endurance athletes range from 20% (5) to as high as 60% (5,6).

A study from this year (5) assessed the iron status of 55 healthy female college athletes (age 18-25) in a variety of sports. The hemoglobin of all subjects was normal (so no athletes were anemic) however 24% of the athletes had serum ferritin levels less than 15 ?g/L and 10% had levels less than 12 ?g/L (still somewhat lower than other published estimates ranging from 20-60%). Also 25% of the females surveyed consumed less than 66% of their dietary requirement (9 athletes took an iron supplement ranging from 18-150 mg/day, and 14 athletes took a multivitamin).

In 2003 Cowell (6) et al. surveyed 54 NCAA Division I schools to determine their practices in screening and treating female athletes for iron deficiency. Only 43% of these institutions reported screening female athletes for iron deficiency. Furthermore, variability exists in the criteria for diagnosis as well as the treatment protocols. There is clearly a need for the development of standard protocols for assessment and treatment of iron deficiency in athletics.

Sources of Iron Loss

Exercise may contribute to iron loss by the following means:

  • Increased gastrointestinal blood loss after running (2,4, 7)
  • Hematuria (presence of hemoglobin or myoglobin in the urine) as a result of the red blood cell rupture caused by the foot striking the ground while running or by mechanical stress in the muscle (3,4)
  • Sweat may account for iron losses of 0.3-0.4 mg per litre during exercise (3,7)
  • Another significant source of iron loss for women is menstruation. Iron deficiency is almost inevitable when menstrual bleeding is heavy (greater than 60 mL) and/or if the menstrual cycle lasts longer than five days. Many women do not even know if their menstrual losses are excessive (7).
  • Iron status has been shown by some studies to be adversely affected by physical activity, where as other studies have not shown this effect (5).

Supplements

The most common iron tablet is ferrous sulfate. Fumarate and gluconate are also sometimes used (9). The choice to take supplements should be based on hematological evaluation (3,4). Despite some studies reporting no benefit of supplementation beyond improving iron status (5), there is sufficient evidence to suggest serious athletes with low serum ferritin should begin taking iron supplements (2,7). However, the issue of what constitutes a low serum ferritin level remains debatable. Chatard et al. suggest supplementation be initiated if ferritin drops below 12-20 ?g/L for 1-3 months. Neilsen et al concluded that a level below the lower level of normal (35 ?g/L) necessitates supplementation. Certain groups of people including female distance runners, those with heavy menstrual blood flow, athletes who begin high altitude training and athletes who restrict Caloric intake are considered to be at high risk for iron deficiency and may also need to consider supplementation (3). Athletes with normal iron status, as indicated by either serum ferritin or hemoglobin) should not take iron supplements (3,7).

If the decision to supplement has been made, several points should be noted. A daily dose of 50-100 mg is recommended (2). The iron in a multivitamin supplement is not as well absorbed as administering the iron alone, particularly if calcium is part of the preparation or if it is consumed with tea, coffee or a meal (4). It may take a minimum of two months (2) to four months (1) of supplementation to replenish stores and overcome deficiency. One suggested course of supplementation is 100 mg of iron per day in the ferrous form, 10-20% of which is absorbed by the intestine, for 20 consecutive days per month (7). An alternative course of action has been proposed by The International Nutritional Anemia Consultatitive Grroup/WHO/UNICEF (9). Because of concerns surrounding daily supplementation (i.e. toxicity, non-compliance) this group investigated the efficacy of weekly supplementation regimes. A statistical analysis of data from studies examining this issue concluded that both daily and weekly iron supplementation reduced the prevalence of anemia and iron deficiency. The group published guidelines for the use of iron supplements to prevent and treat iron deficiency anemia including, 60 mg/day for adolescents and adults (plus 400 ?g/day of folic acid for women of childbearing age). They concluded that iron supplements should be taken daily to treat anemia, but weekly iron supplements could be an effective way to prevent deficiency.

Supplementing with iron may cause problems in some people such as gastrointestinal distress and constipation (4,7). Limited amounts of information show that high dose iron supplements (i.e. 120 mg or more) were associated with more constipation, nausea, diarrhea and vomiting (9). It is possible for excessive levels to become toxic (4,7), overload being indicated by a serum ferritin level of 200 ?g/L or higher. However this situation is uncommon (1).

Dieticians' Recommendations
Female athletes routinely cite iron status as their primary nutritional concern. The sentiment is not unwarranted, as many female athletes do not meet their dietary requirement for iron.

The final stage of iron deficiency is a reduced hemoglobin concentration referred to as iron deficiency anemia. There is substantial evidence that this condition will impair athletic performance.

Iron deficiency without anemia is the predecessor for to anemia. The evidence is not clear as to whether or not this condition leads to decreased athletic performance. A significant reason for this polarity is that a standard cut-off value to diagnose low iron stores has not been established.
The decision to initiate iron supplementation should not be made without first having blood work done. The presence of anemia (due to iron deficiency) clearly calls for supplementation. Despite the lack of unanimous support from the studies conducted, the presence of iron deficiency alone has been sufficient for some researchers to recommend supplementation. The specific supplementation regime can be tailored to the individual athlete.

To optimize iron status athletes, particularly females, should include beef and dark poultry in their diet, and consume foods such as whole grains, dried fruits, baked potato, beets, spinach and broccoli with meat or vitamin C sources (like citrus fruits).

Reference List
Clark, N. (2003). Nancy Clark`s Sports Nutrition Guidebook 3rd Ed. Champaign, IL.; Human Kinetics
Neilsen P & Nachtigall, D. (1998). Iron supplementation in athletes: current recommendations. Sports Medicine, 26(4), 207-215
Williams, MH. (1999). Nutrition for Health, Fitness and Sport 5th Ed. U.S.A.: WCB/McGraw-Hill
Beard, J & Tobin, B. (2000). Iron status and exercise. American Journal of Clinical Nutrition, 72(suppl), 594S-597S
Gropper, SS et al. (2006, Jan). Iron status of female collegiate athletes involved in different sports. Biological Trace Element Research, 109(1): 1-14
Cowell, BS et al. Policies on screening female athletes for iron deficiency in NCAA Division I-A institutions. Int J Sport Nutr & Exerc Metab 13, 277-285, 2003
Chatard, J.C. et al. (1999). Anemia and iron deficiency in athletes: practical recommendations for treatment. Sports Medicine, 27(4), 229-240
Zhu, YI & Haas, JD. (1997). Iron depletion without anemia and physical performance in young women. American Journal of Clinical Nutrition, 66(2), 334-341
Allen, LH. (2002). Iron supplements: scientific issues concerning efficacy and implications for research and programs. Journal of Nutrition, 132(4 suppl): 813S-819S