Importance of iron for health
Iron is an essential mineral for oxygen transport, oxidative metabolism and energy production normal cellular functioning, proliferation and growth, destruction of pathogens, and synthesis of some hormones (e.g. thyroid hormone) and connective tissue. Iron is present naturally in a diverse range of foods, and added to some food products as a dietary fortificant. Iron is also available in some forms as a dietary supplement.
Iron is an essential component of haemoglobin, an erythrocyte protein that transfers oxygen from the lungs to tissues. Most iron in the human body is located in the haemoglobin. Iron is also a component of myoglobin, a protein that provides oxygen to muscles, and most of the remaining iron is stored as ferritin or hemosiderin (a degradation product of ferritin) in the liver, spleen, and bone marrow. In humans, typically only small amounts of iron are lost in urine, faeces, the gastrointestinal tract or via the skin. Losses are greater in menstruating women. Hepcidin, a circulating peptide hormone, is the key regulator of both iron absorption and the distribution of iron throughout the body, including in plasma.
Iron deficiency is considered as the most widespread nutritional deficiency in the world, and is considered the leading cause for the development of anaemia (1). (Anaemia can also be caused by acute and chronic infections that cause inflammation; other micronutrient deficiencies, especially of folate, vitamin B12 and vitamin A; and genetically inherited traits such as thalassaemia (1) ). Iron deficiency can have high public health and economic costs on society. Pregnant women and their young children are among the most vulnerable population groups; though children’s mental and physical development can be delayed by iron deficiency, and the physical work capacity and productivity of manual workers may be reduced (1). These effects can manifest both with or in the absence of anaemia: not all anaemic people are iron deficient and iron deficiency may occur without anaemia.
The prevalence of iron deficiency and anaemia varies in different populations and no consistent relationship between the two can be applied to all populations throughout the world (1). Further, interactions between iron and other dietary factors play a significant role in determining the adequacy of iron nutrition and have important implications for food fortification in developing countries.
Sources of dietary iron
Dietary iron has two main forms: haem and non-haem. Plants and iron-fortified foods contain non-haem iron only, whereas meat, seafood, and poultry contain both haem and non-haem iron. Haem iron is formed when iron combines with protoporphyrin IX, and is always well-absorbed. The absorption of non-haem iron, however, depends on the iron status of the individual consuming the meal, as well as the meal composition itself(2).
Foods that have relatively high iron content include liver, red meat, beans, nuts, green leafy vegetables, and fortified breakfast cereals, but the absorption of iron from dietary intake is very variable (2). Fortification iron, e.g. ferrous sulphate and ferrous fumarate may be added to foods including cereal products, infant foods, condiments, milk and dairy products and meal replacement foods (2).