A low number of red blood cells. Red blood cells contain haemoglobin, and so your haemoglobin will also be low. Haemoglobin carries oxygen around the body. So if you are anaemic, you may feel tired or breathless.
Cancer Research UK is a registered charity in England and Wales (1089464), Scotland (SC041666) and the Isle of Man (1103). A company limited by guarantee. Registered company in England and Wales (4325234) and the Isle of Man (5713F). Registered address: Angel Building, 407 St John Street, London EC1V 4AD.