Iron is an important part of the red blood cells that carry oxygen to all the cells of the body. If we don't have enough iron we easily run short of breath, get tired and have problems concentrating.
The reasons may be losses and/or not enough intake
In healthy individuals the average iron absorbed is 1 mg daily for men, 1.5 - 2.5 mg daily for women and during pregnancy 2 - 3 mg daily corresponding to a total of 500 - 1 000 mg per month Iron requirements should compensate for demand during growth, pregnancy and physiological and pathological losses.
Iron cannot be substituted by anything else.
Our bodies contain 4-5 grammes of iron. It may be difficult to get enough of this important nutrient unless meat courses are part of the diet. Fruit, cereals and vegetables contain relatively little of useful iron. If you’re suffering from low iron, no amount of vitamins or any other supplement is going to change it.