The Evidence on Anemia, Without the Hype

Key takeaways

• Diagnosed by: low hemoglobin on a complete blood count (CBC)
• Red cell size (MCV): narrows the cause considerably
• Most useful single change: Ask what type of anemia it is, not just that you are anemic.
• Commonest mistake: Taking iron supplements without a blood test.
• See a doctor if any of the signs under "When to speak to a doctor" below apply to you.

What it is

Too little hemoglobin to carry oxygen efficiently, from many possible causes. It sits within Blood Health. The table below gives the figures guidance actually works from.

The numbers, in one place

What helps

These are worth doing. None of them needs to happen all at once.

• Ask what type of anemia it is, not just that you are anemic
• Ask whether ferritin, B12 and folate were checked alongside the blood count
• Find the cause before starting long-term supplements
• Complete any prescribed course in full, which lasts longer than symptom relief

What to avoid

The usual wrong turns. Some are more tempting than others.

• Taking iron supplements without a blood test
• Assuming anemia is always caused by diet
• Ignoring it because symptoms came on slowly

In depth

Hemoglobin is the iron-containing protein inside red blood cells that picks up oxygen in your lungs and releases it in your tissues. Your bone marrow makes red cells continuously, and each one circulates for about four months before it is recycled. Anemia means the amount of hemoglobin in your blood has fallen below the expected range for your age and sex, so less oxygen reaches your muscles, brain and heart with each heartbeat.

Every anemia comes from one of three broad problems: the marrow is not making enough red cells, red cells are being destroyed too early, or blood is being lost. Shortages of iron, vitamin B12 or folate, kidney disease and long-term inflammation all reduce production. Inherited conditions such as sickle cell disease, and some immune reactions, destroy cells early. Heavy periods and slow bleeding from the stomach or bowel are the most common causes of loss in adults.

Iron deficiency is the most common type in the US. Because the body adapts to slowly falling hemoglobin by increasing heart rate and changing how oxygen is released, a gradual anemia can become quite marked before you notice it. That is also why the cause matters more than the number: a mild anemia from unexplained bleeding can be more important than a lower one from a known, treated cause.

Signs and symptoms

• Tiredness and low energy that rest does not fix
• Shortness of breath or a pounding heart on exertion
• Pale skin, or paleness inside the lower eyelids
• Dizziness or lightheadedness, especially on standing
• Headaches, cold hands and feet, or difficulty concentrating
• Cravings for ice or nonfood items, a sign of iron deficiency
• Restless legs at night, which can be linked to low iron

Causes and risk factors

• Heavy menstrual periods
• Slow bleeding from the stomach or bowel, including from ulcers, polyps or cancer
• Low dietary iron, B12 or folate, or poor absorption such as in celiac disease
• Pregnancy, which raises iron needs
• Chronic kidney disease, which reduces the hormone that stimulates red cell production
• Long-term inflammatory conditions, infections or cancer
• Inherited conditions such as sickle cell disease and thalassemia

How it is checked

A complete blood count (CBC) shows your hemoglobin, hematocrit and red cell size (MCV), and often a measure of how varied the cells are in size. A reticulocyte count shows whether your marrow is responding by making new cells. Ferritin, which reflects iron stores, is the most useful test for iron deficiency; a low ferritin confirms it, although inflammation can push ferritin up and hide a deficiency.

Depending on the pattern, your doctor may check B12, folate, kidney function, thyroid function and markers of red cell breakdown. If iron deficiency has no obvious explanation, especially in men and in women after menopause, the next step is usually looking for blood loss in the digestive tract, which may mean a colonoscopy, an upper endoscopy and testing for celiac disease.

Treatment and support options

Iron by mouth

For iron deficiency, your doctor may suggest iron tablets taken daily or every other day. Taking them with a source of vitamin C and away from tea, coffee, dairy and calcium helps absorption. Constipation, nausea and dark stools are common side effects; changing the timing or formulation can help. Hemoglobin usually starts to rise within a few weeks, but treatment continues for months to refill iron stores.

Iron through an IV

If you cannot tolerate or absorb iron tablets, have ongoing blood loss, have chronic kidney disease or need faster correction, iron can be given through an IV in a clinic. It refills stores in one or a few sessions. Your doctor will explain the small risk of reactions and monitor you during the infusion.

Treating the underlying cause

Correcting the cause prevents the anemia from returning. That may mean treatment for heavy periods, removal of a bleeding polyp, a gluten-free diet for celiac disease, or management of kidney disease. For anemia linked to chronic kidney disease, your doctor may discuss medicines that stimulate red cell production alongside iron.

B12 and folate replacement

Anemia from B12 or folate deficiency is treated by replacing the missing vitamin, by shots or tablets depending on the cause. Blood counts often begin to improve within days. It is important to check B12 before treating with folic acid alone, because folic acid can correct the blood count while B12-related nerve damage continues.

Blood transfusion

Transfusion is reserved for severe or rapidly developing anemia, significant bleeding, or anemia causing chest pain or breathlessness at rest. It works immediately but does not fix the cause. For most people with iron deficiency, iron replacement is safer and more appropriate.

Prevention

• Eat iron-rich foods such as lean meat, poultry, fish, beans, lentils and fortified cereals
• Pair plant sources of iron with vitamin C, such as citrus fruit or peppers
• See your doctor about heavy periods rather than accepting them as normal
• Take a prenatal vitamin with iron during pregnancy as advised
• Keep up colorectal cancer screening from age 45
• Limit cow's milk in toddlers to the amount your pediatrician recommends

Day to day

While your levels recover, pace yourself. Spreading tasks through the day, building activity up gradually and getting regular sleep help you cope with reduced stamina. Energy often returns before blood tests are fully normal, but keep taking any prescribed treatment for the full course, because stopping early leaves iron stores low and the anemia tends to return.

Keep the follow-up tests your doctor arranges. A repeat blood count after treatment confirms that the cause has been addressed. If your anemia keeps coming back, that is a reason to look harder for the cause, not to keep taking supplements indefinitely. Keep a copy of your results so trends are easy to see if you change doctors.

For specific groups

Pregnancy

Blood volume and iron needs increase during pregnancy, so iron deficiency anemia is common. Your blood count is checked at prenatal visits, and your provider may recommend iron in addition to your prenatal vitamin. Treating anemia before delivery helps you cope with blood loss at birth.

Infants and toddlers

Iron is vital for brain development. The AAP recommends screening for anemia around the first birthday. Drinking large amounts of cow's milk can cause iron deficiency in toddlers because it is low in iron and fills them up. Iron-rich foods and appropriate milk limits help prevent it.

Older adults

Anemia is common with age but should not be accepted as normal. It is linked to falls, worsening heart failure and reduced function. Causes often include chronic disease, kidney decline, nutrient deficiency and bleeding, so it deserves the same investigation as at any age.

Questions to ask your doctor

• What type of anemia do I have, and what is causing it?
• Were my ferritin, B12 and folate checked?
• Do I need tests to look for bleeding in my digestive tract?
• How should I take my iron, and for how long?
• When will we repeat my blood count?
• Would IV iron be better for me?

More questions, answered

How long does it take to recover from iron deficiency anemia?

Hemoglobin usually starts rising within a few weeks of starting iron, and many people feel better within a month or two. Refilling iron stores takes longer, often several months, so your doctor may want you to continue after your hemoglobin is normal. Recovery is slower if blood loss continues.

Why are my stools black on iron tablets?

Iron tablets commonly turn stools dark green or black, and this is harmless. Black, tarry, sticky stools with a strong smell can indicate bleeding in the upper digestive tract, especially with dizziness or weakness. If you are unsure, contact your doctor; with fainting or vomiting blood, call 911.

Can I fix anemia with diet alone?

Diet helps prevent iron deficiency, but once you are anemic, food alone usually cannot refill iron stores quickly enough. Supplements or IV iron are generally needed, along with treating the cause. A good diet then helps keep levels up afterward.

Can anemia cause hair loss?

Iron deficiency is linked to hair shedding in some people, and hair often improves once iron stores are restored. Many other factors also cause hair loss, including thyroid disease and stress, so it is worth discussing with your doctor if it persists.

Can I donate blood if I have anemia?

No. Your hemoglobin is checked before every donation, and you cannot donate if it is too low. Once your anemia has been treated and the cause found, you may be able to donate again. Frequent donors are at risk of low iron, so ask about it if you donate often.

Is anemia inherited?

Some types are, including sickle cell disease, thalassemia and certain enzyme or membrane disorders of red cells. Most anemia in adults, though, is caused by iron deficiency, blood loss, chronic disease or vitamin deficiency. Mention any family history of anemia or blood disorders to your doctor.

Related topics

• Colorectal Cancer: Sorting the Evidence From the Noise (Cancer Awareness)
• Heavy Periods: What the Evidence Actually Says (Women's Health)
• Celiac Disease: What Published Guidance Supports (Digestive Health)
• Smoking and the Heart: What Published Guidance Supports (Heart Health)

Where to go next

• Why Anemia Matters, Explained Simply
• Anemia: What to Do, in Order
• Anemia — the reference entry
• Blood Health: The Complete Guide
• Vitamin B12 Deficiency: Sorting the Evidence From the Noise
• The Evidence on Blood Clots, Without the Hype

When to speak to a doctor

See your doctor promptly for fatigue with shortness of breath or palpitations; iron deficiency in a man, or in a woman after menopause, needs investigation of the digestive tract rather than supplements alone. Call 911 for chest pain, shortness of breath at rest, vomiting blood, or black tarry or bloody stools with dizziness or fainting.

Where this comes from

• National Heart, Lung, and Blood Institute — Anemia
• American Society of Hematology — Anemia

How this page was put together

Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.

Medical disclaimer

This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.