Iron - are you getting enough?

Why is iron important?

Iron is required for a number of key functions in the body:

• Iron is an important component of haemoglobin and myoglobin.  Haemoglobin transports oxygen in the blood.  Myoglobin transports oxygen in the muscles.
• Iron is involved in the electron transport system.  This system controls the release of energy from cells.
• Iron is required for red blood cell production.
• Iron is required for a healthy immune system

Inadequate iron in the body can impair aerobic metabolism by decreasing the delivery of oxygen to tissues and reducing the capacity of muscles to use oxygen for the oxidative production of energy. 

Where does iron come from?

The body is unable to manufacture iron therefore the body’s iron needs must be fully supplied by the food we eat.  Although iron is widely distributed in foods, some sources are better absorbed than others. The best sources of iron are foods with a high iron content and high iron bioavailability (i.e. are well absorbed). 

Iron absorption is best (15-18%) from foods that contain haem iron.   Red meat, seafood and poultry are the best sources of haem iron.

Iron absorption from foods that contain non-haem iron is much lower (<5%).  Non-haem iron is predominantly found in plant foods such as cereals, vegetables, legumes and nuts.  The absorption of non-haem iron can be improved by combining sources of haem iron with non-haem iron. Including vitamin C-rich foods with meals (e.g. juice or fruit with breakfast, capsicum in a stirfry, salad or fruit with a sandwich) also enhances absorption of non-haem iron.

Some substances in food inhibit the absorption of iron.  Excessive intakes of tea, coffee and bran have an inhibitory effect.  Consumption of these foods may need to be modified when iron status is poor.

Major contributors of iron in the Australia diet are meat, fish, poultry, iron-enriched breakfast cereal and bread.  Dried fruit, sweet corn, green leafy vegetables including broccoli, silver beet, spinach and Chinese green vegetables are other good sources of iron.

 

Haem Iron
Food	Serve	mg Iron
Liver Liver pate Beef Chicken Fish Oysters Salmon	100 g cooked 40 g (2 Tbsp) 100g cooked 100g cooked 100 g cooked 100g 100g	11.0 2.0-3.0 4.0 1.2 0.6-1.4 3.9 1.5

 

 

Non-haem Iron
Food	Serve	mg Iron
Eggs Breakfast cereal (fortified) Wholemeal bread Spinach Lentils/kidney beans Tofu Sultanas Dried apricots Almonds	100 g (2) 30 g (1 cup) 60g (2 slices) 145g cooked 100 g cooked 100g 50g 50 g 50 g	2.0 2.5 1.4 4.4 2.5 1.9 0.9 2.0 2.1

Source: Burke L, Complete Guide to Food for Sports Performance, Allen and Unwin, 1995

How much iron do I need?

The following table provides the Recommended Dietary Intake (RDI) for iron in Australia:

	Males	Females
8-11 years	6-8 mg/day	6-8 mg/day
12-18 years	10-13 mg/day	10-13 mg/day
adults	7 mg/day	12-16 mg/day (menstruating) 5-7 mg/day (non-menstruating)
pregnant		+10-20 mg/day

Specific iron requirements for athletes participating in different sports are currently unknown. Endurance athletes (particularly runners) are thought to have the highest requirements due to high iron losses.  Some studies recommend iron intakes of 17.5 mg/day for male distance runners and 23 mg/day for normally menstruating female distance runners.  These intakes are particularly high and may not be achievable especially for females with lower energy intakes.

Are athletes more at risk?

Athletes have a high risk of iron depletion for several reasons:

1. High requirements

• Increased red blood cell mass means athletes have higher iron needs.  Needs are particularly high during times of growth.

2. Increased losses

• Iron is lost in the sweat.  Athletes with high sweat losses have higher iron losses.
• Iron can be lost through gastrointestinal bleeding.  Gastrointestinal bleeding commonly occurs during strenuous exercise due to minor damage to the stomach and intestinal lining.  Some gastrointestinal blood loss can be caused by the habitual use of anti-inflammatory drugs.
• Mechanical trauma such as footstrike haemolysis (repeated pounding of the feet on hard surfaces) can destroy red blood cells during activities such as running.

3. Dietary Issues

• Iron intake is often sub-optimal in athletes with restricted food intakes:
  • Trying to survive on low kilojoule intakes (below 8 300 kj, 2000 cal) in an attempt to minimise body weight
  • Poorly balanced vegetarian diets
  • Avoidance of meat, chicken or fish in an effort to enhance carbohydrate intake or in the mistaken belief that it is fattening
  • High reliance on snack and convenience foods and failure to consume regular meals
  • Avoidance of commercially fortified foods such as breakfast cereals

How will I know if I have a problem?

Iron depletion is a continuous process that ultimately results in iron deficiency anaemia if untreated.  Iron deficiency anaemia is a condition where iron is depleted to such an extent that the manufacture of haemoglobin and red blood cells is limited.  It is associated with symptoms such as fatigue, weakness, breathlessness, and impaired aerobic capacity.  It is easy to confuse many of these symptoms with conditions such as the flu, overtraining or ‘being run-down’. 

One-off blood tests are difficult to interpret when it comes to iron status.  Correct diagnosis requires an assessment of habitual dietary intake, clinical symptoms and ongoing monitoring of blood levels.  A number of factors are usually taken into account when assessing iron status.  These include serum iron, ferritin, transferrin, transferrin saturation, haemoglobin and full blood count. A skilled practitioner is needed to accurately assess iron status.  Many athletes have routine blood monitoring to assess iron status.  Iron depleted athletes can quickly develop iron deficiency anaemia if not detected early.  Regular monitoring allows the sports physician to keep track of individual changes and trends. 

What is sports anaemia?

Iron status is difficult to assess, particularly from one-off blood measurements.  Hard exercise results in an increase in the volume of plasma in the blood.  This can dilute haemoglobin levels and incorrectly suggest that there is a problem with iron status.  This condition is known as ‘sports anaemia’.  It is most likely to occur in the early stages of a training program or when training load is increased.  Sports anaemia does not need treatment.  It is usually transitory and is unlikely to affect performance. 

How is iron deficiency treated?

Iron supplementation is needed to recover depleted iron stores and an iron-rich diet is needed to maintain the increase in iron stores.  Typically, supplementation involves 100-300 mg of iron per day in conjunction with vitamin C to enhance absorption.  Full recovery is slow and can take as long as 3 months.  Blood levels should be reviewed after 10-12 weeks and supplementation ceased when measurements return to usual ranges.

A diet rich in iron is needed to prevent iron depletion reoccurring.  A dietitian can provide specific feedback.  However, the following tips will help:

• Choose breakfast cereals that contain added iron.
• Consume red meat such as beef, lamb or kangaroo 3-4 times each week.  Small amounts (80-100 g) are sufficient.  Think about creative ways to consume meat such as in sandwiches, stirfries and soups if you find it difficult to eat large chunks of meat.  Shellfish, canned fish and poultry are also useful sources of iron.
• Add vitamin C-rich foods (fruit, juice, capsicum, broccoli, cabbage, cauliflower) to meals to enhance the absorption of iron.
• For vegetarian meals, choose iron-rich foods such as legumes and add vitamin C-rich foods to enhance the absorption of non-haem iron
• Avoid or limit intake of iron inhibitors such as bran and wheat germ.
• Avoid drinking strong tea and coffee with meals.  It is OK between meals but not with meals.

Should I take an iron supplement?

It is extremely difficult to correct iron deficiency anaemia solely with an iron-rich diet.  Supplementation (under the guidance of your medical practitioner) is usually required to treat a diagnosed iron deficiency.

Often athletes experiencing symptoms such as fatigue or lethargy turn to iron supplements to correct or prevent the problem.  Currently, there is little evidence to indicate that iron supplementation improves aerobic capacity in athletes with depleted iron stores, who do not have anaemia.  Further research is needed before iron supplementation is recommended for athletes without clinically diagnosed iron deficiency anaemia. Regular, inappropriate use of iron supplements can interfere with zinc and copper absorption and may have negative effects on the immune system. 

Iron supplements should not be taken without medical advice.

A small percentage of the population has a condition called haemochromatosis.  In this condition, iron accumulates in tissues causing damage and disease. Haemochromatosis often goes undiagnosed for many years. Iron supplementation is dangerous for people with haemochromatosis.

Some athletes have been known to have iron injections in order to rapidly increase iron stores.  Research indicates performance is not improved by iron injections.  There is a risk that anaphylactic shock can occur with iron injections.  This can be fatal.

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Written by Michelle Minehan and the Department of Sports Nutrition, AIS © Australian Sports Commission 2004