Anemia and Iron Deficiency: Tiredness and Testing

What this page covers

Anemia means having fewer healthy red blood cells than normal, so the body gets less oxygen-rich blood. That lack of oxygen can make you feel tired or weak. [1] Iron deficiency anemia is the most common type. [2] This page is educational. Only a clinician can tell whether you have it, and why.

Why tiredness alone cannot tell you

NHS lists tiredness and lack of energy, shortness of breath, noticeable heartbeats, paler skin and headaches as symptoms of iron deficiency anemia. [2] Many other conditions cause the same feelings, so a blood test is how anemia is checked, not symptoms alone. The usual first test is a full blood count, which shows whether the number of red blood cells is normal. [2]

Why the cause matters

Anemia can be a sign of something else. NHLBI notes it may come from diet, medicines, or another medical condition, and may be a sign of a more serious condition such as bleeding in the stomach, kidney disease, cancer, or autoimmune disease. [1] NHS names heavy periods and pregnancy as very common causes of iron deficiency anemia, and bleeding in the stomach and intestines as another common cause. [2] If the reason is not clear, a clinician may do further tests or refer you. [2] For heavy periods, see Heavy or irregular periods, and for life-stage needs see Nutrition for women: iron, folate, calcium and vitamin D.

Established care

When a blood test shows low red blood cells, NHS says iron tablets are recommended, usually for about 6 months, with repeat blood tests to check levels return to normal. [2] Common side effects include constipation or diarrhea, stomach pain, heartburn, nausea and darker stools. [2] Untreated iron deficiency anemia can raise the risk of infection and heart or lung complications, and carries risks in pregnancy. [2]

Food and iron

Good iron sources include red meat, beans, nuts, dried fruit and fortified breakfast cereals; dark-green leafy vegetables also appear on NHS lists. [3] [2] MedlinePlus says iron from plants and supplements is harder to absorb, that vitamin C-rich foods help absorption, and that black tea contains substances that bind iron. [4] NHS also lists tea, coffee, dairy and foods high in phytic acid as things that can make absorption harder in large amounts. [2] See Leafy greens, Legumes and Fortified foods.

What about iron when you are not anemic?

Evidence: mixed to promising but limited. In a Swiss trial, 144 non-anemic women aged 18 to 55 with unexplained fatigue took either iron (80 mg a day of elemental iron, study amount) or placebo for four weeks. Fatigue fell 29% with iron and 13% with placebo, and the benefit appeared only in women with ferritin (one of the blood test results) at or below 50 micrograms per liter. [5] This was one four-week trial in women, so it cannot be applied to everyone. It also shows why ferritin should be measured first.

Why not just start iron pills?

• You may not be low. Tiredness has many causes. [6]
• Too much iron can harm. Haemochromatosis is an inherited condition in which iron slowly builds up, and people with it are usually advised to avoid iron or vitamin C supplements. [7] Fatigue is one of its symptoms. [7]
• You could miss the cause. If the cause is bleeding, treating the numbers alone does not find it. [2]
• Iron is dangerous to children. An overdose in a young child can be fatal, so keep iron tablets out of reach. [2] If a child may have swallowed iron, see Poisoning: what to do first. In the US, Poison Help is 1-800-222-1222, and in an emergency call 911.
• Side effects are common. High doses of iron can cause constipation, nausea, vomiting and stomach pain. [3]

Read How interactions work before taking iron with other medicines or supplements, and see Fatigue: when to get help.

When to get help

See a clinician if you think you may have iron deficiency anemia. [2] Also see one if tiredness lasts a few weeks without a clear reason. [6]