Iron physiology and metabolism

Body iron stores

The body contains 2.5–4 g of iron, with about 2/3 present in red blood cells.

Storage iron is held mostly in the liver and levels vary according to age and gender.(1) Approximate iron storage amounts include:(2)

  • 300 mg in premenopausal females
  • 600 mg in post-menopausal females
  • 800 mg in males

 

Iron metabolism

The human body obtains iron from the diet, absorbing approximately 1–2 mg a day from an average daily intake of 10–15 mg. The body also loses 1–2 mg per day in urine, sloughed skin cells, menstruation, etc. The majority of the body’s iron is located in red blood cells and is recycled with their senescence.

Modified with permission from Greg Anderson, Queensland Institute of Medical Research, Australia, 2011.

 

Iron absorption

Iron absorption is influenced by a number of factors including:

  • the amount of iron in the diet
  • the form of iron (haem iron is more readily absorbed than non-haem)
  • the presence of enhancers or inhibitors
  • medications
  • disease states affecting the gut, eg, coeliac disease, surgery
  • physiological limitations

Non-haem iron is found in plants such as green leafy vegetables, wholegrain cereals, nuts and dried fruits. Only about 5% of non-haem iron is absorbed. It is also strongly influenced by enhancing or inhibiting factors.

Haem iron is found in meat, fish and poultry products. It is absorbed much more readily than non-haem iron – about 20% is absorbed. The best source of haem iron is red meat.

 

Enhancers

Foods which enhance the absorption of iron include those containing;

  • vitamin C, eg, broccoli, tomatoes, capsicum, oranges, berries, grapefruit and kiwi fruit
  • organic acids, eg, grapes, tomatoes, citrus fruits and pineapple
  • haem iron

 

Inhibitors

Foods which inhibit the absorption of iron include those containing:

  • phytates, eg, legumes, cereals, nuts, soy protein, cocoa and cola drinks
  • polyphenols, eg, red wine, coffee, tea, cocoa and smoked food
  • oxalic acid, eg, spinach, rhubarb, sweet potato, buck wheat, parsley, leeks and berries
  • calcium eg, dairy and soy products such as milk and cheese
 
References
  1. Zacharski LR, Ornstein DL, Woloshin S, Schwartz LM. Association of age, sex, and race with body iron stores in adults: analysis of NHANES III data. Am Heart J 2000;140:98–104.
  2. Cook JD, Skikne BS, Lynch SR, et al.: Estimates of Iron Sufficiency in the US Population. Blood 1986;68:726–731.

 

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