Iron is essential for the formation of haemoglobin in red blood cells; haemoglobin binds oxygen and transports it around the body. Iron is also an essential component in many enzyme reactions and has an important role in the immune system. In addition, it is required for normal energy metabolism and for the metabolism of drugs and foreign substances that need to be removed from the body.
A lack of dietary iron depletes iron stores in the body and this can eventually lead to iron deficiency anaemia. In particular, women of child bearing age and teenage girls need to ensure they consume adequate dietary iron because their requirements are higher than those of men of the same age. Also, loss of blood due to injury or large menstrual losses increases iron requirements in the short term. Data from the NDNS indicate that average daily iron intakes from foods are below the RNI for women in all age groups, except for older women (over the age of 54 years). A very significant proportion of younger women (2 out of 5) have intakes below the lower reference nutrient intake (LRNI) i.e. intakes that are likely to be inadequate.
Currently, there are no recommendations for increasing iron intake during pregnancy as the extra demand should be offset by pre-existing body stores, lack of menstrual blood loss and the increased intestinal absorptive capacity of the mother during the second and third trimesters of pregnancy.
More than 2 billion people worldwide suffer from iron deficiency anaemia, making it the most common nutritional deficiency condition.
As with some other minerals, under normal circumstances absorption of iron is tightly controlled as iron can have adverse effects owing to its ability to generate oxygen free radicals. However, 1 person in 200 of northern European descent is genetically predisposed to the iron loading disease haemchromatosis.
Dietary iron is found in two basic forms. Either as haem iron (from animal sources) or non-haem iron (from plant sources). Haem iron is the most bioavailable form of iron. However, the predominant form of iron in all diets is non-haem iron, found in cereals, vegetables, pulses, beans, nuts and fruit. Absorption of non-haem iron is affected by various factors in food. Phytate (in cereals and pulses), fibre, tannins (in tea) and calcium can all bind non-haem iron in the intestine, which reduces absorption. However, vitamin C, present in fruit and vegetables, aids the absorption of non-haem iron when eaten at the same time, as does meat.
Liver, red meat, pulses, nuts, eggs, dried fruits, poultry, fish, whole grains and dark green leafy vegetables are all sources of iron. Since the 1950s in the UK, all wheat flours (other than wholemeal) have been fortified with iron and many breakfast cereals are also fortified with iron and so contribute to iron intake, However, the nature of these foods imposes limitations on the type of iron that can be used as a fortificant and so low bioavailability may be an issue, as suggested in the recent draft report on iron from SACN here.
A draft review of iron and health has recently been published by the Government’s advisory committee, SACN here.