Role of Iron in human body

Iron is an essential mineral, with several important roles in human body
The human body needs iron to make the oxygen-carrying proteins haemoglobin and myoglobin, electron transport and iron-containing enzymes (functional iron). Iron-containing enzymes are essential for the synthesis of DNA, RNA and synthesis of collagen which is essential for healthy gums, teeth, cartilage and bones.  
Iron containing enzymes help in the conversion of beta carotene of plants such as carrots, red peppers and apricots into the active form of vitamin.

During the 17th century, iron was used to treat chlorosis (green disease), a condition often resulting from the iron deficiency.

As our body can’t produce iron itself we need to consume sufficient amounts of iron in our diet.

Good sources of iron

Eggs (especially egg yolks), Liver, Lean red meat (especially beef), Oysters, Poultry, dark red meat)
Dried fruits: Prunes, Raisins, Apricots
Legumes:  Lima beans, Soybeans, Dried beans and peas, Kidney beans
Seeds: Almonds, Brazil nuts
Vegetables: Broccoli, Spinach Kale, Collards, Asparagus, Dandelion greens
Whole grains: Wheat, Millet, Oats, Brown rice
25% of the iron in animal food is absorbed by the body while less than 10% of non-haem iron comes from plant sources such as vegetables, dried fruits, and whole grain bread.
Strict vegetarians are often at risk from iron deficiency anaemia.
However large amounts of iron from plant sources is absorbed if they are accompanied by peppers or foods rich in vitamin C (such as citrus, strawberries, tomatoes, and potatoes)
Mixing some lean meat, fish, or poultry with beans or dark leafy greens at a meal also improves absorption of vegetable sources of iron up to three times. Cooking foods in a cast-iron skillet can also help to increase the amount of iron provided.

Some foods such as commercial black or pekoe teas  reduce iron absorption as they contain substances that bind to dietary iron, so it cannot be used by the body.
The amount of iron needed is:  
8.7mg a day for men    
14.8mg a day for women

The human body stores some iron to replace any that is lost. However, low iron levels over a long period of time can lead to iron deficiency anaemia.

Symptoms include lack of energy, shortness of breath, headache, irritability, dizziness, or weight loss.
Physical signs of iron deficiency are a pale tongue and spoon-shaped nails.

The genetic disorder called hemochromatosis affects the body's ability to control iron absorption. This leads to accumulation of iron in the body over a long period causing Iron poisoning. Such a condition is called Siderosis.
This condition may be the result of repeated blood transfusions, regular drinking of alcoholic drinks brewed in iron vats. It is characterised by the greyness of the skin.

Side effects of taking high doses (over 20mg) of iron include: constipation, nausea, vomiting, and stomach pain.
Very high doses of iron can be fatal, particularly if taken by children.