What should you know about fainting from low iron?

Iron helps your body make haemoglobin, the part of red blood cells that carries oxygen. When iron deficiency progresses to anaemia, you may feel tired, breathless with activity, dizzy, cold or aware of a fast heartbeat. Standing suddenly, heavy menstrual bleeding, poor intake or another source of blood loss can make symptoms more noticeable. Low iron alone does not explain every blackout, so fainting should not be self-diagnosed from tiredness.

A clinician can check a full blood count and iron-related tests, then look for the reason iron is low. The cause might involve menstrual bleeding, diet, absorption or bleeding elsewhere. Dehydration, hypoglycaemia and heart rhythm conditions such as Atrial Fibrillation are separate possibilities that may need consideration.

If you feel faint, lie down with your legs raised and avoid walking alone. Drink water if you are alert and swallowing safely. Book an appointment for persistent fatigue, breathlessness, recurrent dizziness or a blackout. Do not start high-dose iron without advice: the right preparation and duration depend on your blood results and the cause. Keep a note of bleeding, diet, medicines and the circumstances of each episode.

Call emergency services for fainting with chest pain, severe breathlessness, confusion, black or bloody stools, heavy ongoing bleeding, serious injury, new neurological symptoms or a heartbeat that is very fast or irregular. Prompt assessment is also needed if you faint during exertion or remain unusually weak after waking.

Ask which blood tests are needed, whether bleeding could explain the result, how treatment will be monitored and what symptoms mean you should seek urgent help. Tell the clinician if you are pregnant, have digestive symptoms or take medicines that affect bleeding.