Relationship Between Thyroid Diseases And Anemia

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Does hypothyroidism cause anemia?

Hypothyroidism can cause anemia, although it’s not guaranteed to do so. Whilst it’s not fully understood how hypothyroidism can lead to anemia, there are a few theories, which include:¹

  • Reduced bone marrow function: Hypothyroidism can impair the function of the bone marrow, which is responsible for making red blood cells. This is thought to be due to thyroid hormones' direct effects regulating new blood cell creation in the bone marrow.

  • Decreased erythropoietin production: Hypothyroidism can lead to reduced production of erythropoietin, a hormone that promotes the creation of red blood cells.

  • Concomitant deficiencies in vitamins essential for RBC production, such as B12 and folate, can occur in hypothyroidism. These deficiencies are particularly associated with certain autoimmune conditions, like Hashimoto's thyroiditis which can present with hypothyroidism.

Again, hypothyroidism does not cause anemia in all individuals. But if you have hypothyroidism, your doctor will want to periodically check your blood, usually through a complete blood count (CBC) that can also spot other problems.

Does hyperthyroidism cause anemia?

Hyperthyroidism has also been shown to cause anemia. However, the association isn’t thought to be as strong as with hypothyroidism. More research is needed to understand why hyperthyroidism leads to anemia. Currently, the following mechanisms have been put forward:  

  • In hyperthyroidism, the red blood cell mass increases, but the plasma volume expands even more, leading to normochromic, normocytic anemia. Interestingly, serum ferritin concentrations may be elevated despite this anemia.

  • Increased red blood cell breakdown: Hyperthyroidism can shorten the lives of red blood cells, leading to increased breakdown of these cells.

  • Nutrient deficiencies: Hyperthyroidism from autoimmune causes can be associated with nutritional deficiencies, such as iron or vitamin B12, which you need for red blood cell production.

  • Menstrual disturbances: Hyperthyroidism can cause menstrual disturbances, leading to heavy menstrual bleeding, which can result in anemia in women.

Treating an overactive thyroid with surgery or iodine, depending on the cause, can resolve the disease but sometimes results in hypothyroidism, which then needs to be treated with medication.

Can anemia affect thyroid function?

Potentially, yes. Anemia can affect the function of every organ and gland in your body as it reduces available oxygen. Iron is also a very important component of enzymes, actively taking part in the production of thyroid hormones, and therefore it can affect the production of thyroid hormones. 

A meta-analysis (a study looking at all other studies) showed that if you have iron deficiency while pregnant, it can dramatically increase the risk of hypothyroidism and other thyroid disorders, especially if not treated promptly. This shows the importance of ensuring you get sufficient iron if you’re pregnant or trying to become pregnant. Women are also at higher risk of iron deficiency anemia due to red blood cell loss from menstruation.

If you’re diagnosed with anemia, follow your doctor's instructions and take all required supplements and medications to resolve it quickly and prevent any long-term complications.

How is anemia diagnosed?

Anemia is typically diagnosed with a blood test that measures your hemoglobin levels. Hemoglobin is a protein found in red blood cells. A low hemoglobin (2 standard deviations below the mean of your sex & age) indicates that you have anemia. 

The most common form of anemia associated with thyroid conditions is called normocytic normochromic anemia, meaning that the red blood cells look normal in shape and color (as opposed to cells that might look paler in color or too large or small). 

Your doctor will also conduct other blood tests to check for the cause of the anemia, including tests checking for low iron levels and vitamin B12 and folate deficiencies. A regular full blood count is typically ordered by clinicians for anyone with thyroid disease.

The symptoms of anemia include dizziness, lightheadedness, cold hands and feet, pale skin, shortness of breath, and fatigue. Because fatigue is also a symptom of an underactive thyroid, it’s possible that some cases of anemia might be missed. The fatigue and other symptoms might be mistaken for symptoms of the thyroid condition itself. 

Treatment for anemia

The most common form of anemia associated with thyroid disease is normocytic. Normocytic anemia is typically a consequence of other diseases.²

If your anemia is found to be related to low iron, then the go-to treatment for iron deficiency anemia is oral iron supplementation, typically ferrous sulfate. However, these supplements aren’t always well tolerated and can have side effects such as gastrointestinal issues, stomach pain, and nausea. Some individuals may be treated with an IV infusion of iron instead, which also helps bypass iron absorption issues in the gut. 

Iron supplements shouldn’t be taken within four hours of taking levothyroxine, as they can interfere with the absorption of the medication. This includes multivitamins that contain iron. If you’re on levothyroxine, plan to take oral iron supplements later in the day. A high iron diet may also be suggested, with iron-rich food such as red meat, nuts, legumes, fortified breads and cereals, eggs, and leafy green vegetables. 

If your anemia is related to low B12 or folate, your doctor will suggest a treatment plan for those vitamins specifically, sometimes in the form of an injection. Some anemias, such as normocytic anemia, might only correct with the treatment of the thyroid condition. 

Preventing anemia with thyroid conditions

Anemia isn’t a common complication of thyroid conditions, but it’s worth remembering that both are more common in women. The best way to prevent most types of anemia is to ensure that you consume enough iron in your diet, in addition to B12 and folate. It’s also important to take your medications as directed by your doctor and monitor your dosage as requested.

If you’re diagnosed with anemia, the doctor will most likely check your thyroid hormone levels as well, especially if you have good dietary iron intake or have been recently pregnant or going through menopause. 

Treating hyperthyroidism with medication, iodine, or surgery may help resolve associated anemia. However, it can also result in hypothyroidism, meaning you may have to be monitored for anemia.

Preventing thyroid conditions developing from anemia

Promptly treating anemia is vital for minimizing subsequent risks that may be associated with a thyroid condition. If you’re pregnant, talk to your doctor about screening for antenatal and postnatal anemia. The iron demands of the fetus, amongst other causes, increase the risk of anemia during pregnancy. 

It’s also important to talk to your doctor about dietary iron and supplementation to ensure that both you and your baby get enough iron. Teenage mothers are at increased risk, as are vegetarians and vegans.

Iron overdose and your thyroid

It’s possible to consume too much iron. This can happen if somebody takes a higher dose iron supplement combined with medication containing iron. Young children are also at risk, and it’s important to keep iron supplements intended for adults away from children younger than six, especially prescription iron supplements and prenatal supplements.

It’s important to monitor how much iron you ingest, as ingesting too much can cause an overdose. Our bodies require a certain amount of iron, not too much, not too little.

The lowdown

Anemia can be a complication of both hypothyroidism and hyperthyroidism, but it appears to be more common in the former. People with these conditions may require testing for anemia, especially with hypothyroidism, as both conditions can cause similar signs and symptoms. 

If left untreated, anemia, particularly during pregnancy, can exacerbate or be associated with thyroid issues. It’s crucial to undergo screening for anemia if you’re pregnant. Fortunately, there are numerous treatments available for anemia and thyroid conditions. So, if you have any concerns, please consult with your doctor.

Frequently asked questions

Does iron deficiency anemia cause thyroid problems?

Some studies have shown that thyroid regulation can be impaired by iron deficiency anemia, while others have shown that hypothyroidism is common in anemic and iron-deficient individuals.³

Which comes first, hypothyroidism or anemia?

According to one study, “anemia is often the first sign of hypothyroidism.” The low volume of plasma associated with hypothyroidism has the potential to cause false negatives for anemia, so the two diagnoses should be considered in tandem.⁴

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