Why does the human body need iron?

here the most prominent example i know of is its presence in haemoglobin, a protein that makes use of iron to bind oxygen and transport it around the body

 

Nope. Complexes are pretty much all iron does. The above poster's example of hemoglobin is an example of an iron complex.

 

But the iron is still acting through forming a complex - in this case, it is actually a heme porphyrin. The fact that the iron isn't performing a reaction is a mere technicallity - there are many iron-porphyrins that DO catalyze reactions.

 

Enzymes are proteins too. But hemoglobin is not an enzyme. Regardless, I think you've gotten the answer you were seeking, correct?