It increases the number of red blood cells in the body and haemoglobin - a protein that carries oxygen - found in those cells.

There are some, like haemoglobin levels, certain elements of the cardiovascular system that may go away.

He says they may also have higher levels of blood haemoglobin that lead to improved oxygen delivery to where it’s needed in working muscles.

Once we are born, a genetic switch is flipped and we start making "adult haemoglobin".

Being treated for cancer involves a battery of blood tests, as medical staff monitor multiple health indicators such as haemoglobin levels and total white blood cell count.