Iron Deficiency With Thyroid Disease

If you have thyroid disease and fatigue, iron deficiency could be to blame. This is especially true in hypothyroidism (underactive thyroid). But it can also occur with hyperthyroidism (overactive thyroid).

You might see the terms "iron deficiency," "anemia," and "iron-deficiency anemia" used to mean the same thing. But they are different:

• Anemia involves low hemoglobin (a protein in red blood cells).
• Iron deficiency involves low iron.
• Iron-deficiency anemia (IDA) involves low iron and low hemoglobin.

This article looks at iron deficiency and anemia in hypothyroidism and hyperthyroidism, symptoms to watch for, and how it's diagnosed and treated.

Anemia in Hypothyroidism

The low thyroid hormone levels of hypothyroidism suppress the activity of bone marrow, the tissue that makes red blood cells. That lowers the production of red blood cells and triggers anemia.

Research shows as many as 43% of people with symptomatic hypothyroidism have IDA. That's compared to 29% in the general population. Persistent fatigue is a main feature of the condition.

The relationship between iron, red blood cells, and TSH may lead to hypothyroidism by interfering with the thyroid gland's normal function.

Iron Deficiency Alone

Research suggests between 30% and 50% of people on levothyroxine (a thyroid hormone replacement medication) have chronic fatigue with no evidence of anemia.

After ruling out other conditions that cause fatigue, scientists found that iron deficiency was to blame, not IDA. In most cases, the deficiencies were caused by an iron-poor diet that existed before the thyroid diagnosis.

Anemia in Hyperthyroidism

If you have hyperthyroidism, it's likely you have high levels of ferritin, a protein that helps your body store iron. An overactive thyroid gland produces high amounts of ferritin.

It seems logical that increasing iron storage would prevent anemia. The opposite is often true, though. High ferritin appears to trigger an inflammatory response that prevents the body from using iron normally.

This is seen most often in Graves' disease (autoimmune hyperthyroidism). Graves' is associated with IDA and low levels of several kinds of blood cells.

Symptoms of Iron Deficiency

Symptoms of iron deficiency and thyroid disease are similar, making it hard to spot iron deficiency or IDA. They include:

• Persistent fatigue
• Pale skin
• Shortness of breath
• Headaches
• Dizziness
• Heart palpitations
• Dry skin
• Brittle hair and hair loss
• Swelling or soreness of the tongue or mouth
• Restless legs
• Brittle or ridged nails

If your symptoms continue despite treatment for your thyroid disease, ask your doctor to check for iron deficiency or IDA.

Diagnosis

Iron deficiency is diagnosed with a serum ferritin test. It measures the amount of iron storage in your body.

If results are low, you'll be diagnosed with iron deficiency. If they're high, it can help confirm a hyperthyroidism diagnosis. 

Serum ferritin is not a routine part of your complete blood count (CBC). Your healthcare provider will need to order it separately.

If you're paying out of pocket, the test will likely cost between $25 and $50. Results are usually back within two days (depending on your lab).

Treatment

Iron deficiency alongside hyperthyroidism usually doesn't require treatment. It typically goes away with hyperthyroidism treatment.

In other cases, treatments for iron deficiency and IDA are based on the severity of symptoms and serum ferritin test results. It may involve iron supplements and/or an iron-rich diet.

Iron Supplementation

A twice-daily iron supplement is typically prescribed to treat iron deficiency in people with thyroid disease. For mild anemia, the recommended dosage is 60 milligrams twice a day.

Your healthcare provider will likely re-test your serum ferritin after 30 to 60 days of treatment. You can stay on the supplement for up to four months. The dosage is gradually decreased as levels get back to normal.

Especially if you have a largely plant-based diet, you may want to take your iron supplement with vitamin C. Many plant foods contain substances called phytates that keep iron from being absorbed by the intestines. Vitamin C can counter this.

Other supplements that can help iron absorption include:

• Vitamin B6
• Vitamin B12
• Folic acid
• Copper

Side Effects

Iron supplements can cause side effects such as:

• Constipation
• Vomiting
• Diarrhea
• Black stools

A liquid form of iron called Floradix may be easier to tolerate.

Don't take larger doses of iron than your healthcare provider prescribes. That can lead to iron toxicity, especially at dosages above 20 milligrams per kilogram of body weight per day (mg/kg/day).

Dietary Iron Sources

Adding iron-rich foods to your diet can also help get enough iron into your blood. For mild iron deficiency, it may be all the treatment you need. For more extreme cases, it may be recommended along with supplements.

Iron-rich foods include: 

• Red meat
• Organ meat
• Pork
• Poultry
• Mollusks (oysters, mussels, clams)
• Eggs
• Chickpeas
• Pumpkin seeds and sesame seeds
• Lentils
• Dried fruit (raisins, apricots, prunes)
• Iron-fortified bread, pasta, and cereal

Caffeine and calcium can interfere with iron absorption and are best avoided.

Summary

IDA and iron deficiency are common in thyroid disease and can lead to fatigue. Both hypothyroidism and hyperthyroidism can cause iron deficiency and anemia. In turn, iron deficiency can also trigger hypothyroidism.

Iron deficiency/IDA symptoms are similar to those of thyroid disease, making them hard to spot. Your healthcare provider can order a blood test to check your iron levels. It's called a serum ferritin test.

Treatment for iron deficiency includes thyroid replacement medication, iron supplements, and/or a high-iron diet. Vitamins C, B6, B12, and others may improve iron absorption.

A Word From Verywell

When you have two conditions with similar symptoms, it can be hard to tell what's causing what symptoms. Pay attention to any new or worsening symptoms.

Also, look at what does and doesn't improve with thyroid treatments. If you're still fatigued when your thyroid levels return to normal, talk to your doctor about the possibility of iron deficiency and IDA.