Iron is a critical trace mineral involved in producing healthy red blood cells. It's an essential part of hemoglobin, the substance in blood that carries oxygen from your lungs to all your other body cells. Without it, you develop anemia, or iron deficiency, which can cause fatigue and lightheadedness. Iron is also needed to convert T4 to T3. Severe iron deficiency results in a goiter.

In the United States, iron deficiency is quite common, especially among women. Women generally have smaller iron stores and also lose iron each month with menstruation. As a result, iron deficiency affects approximately 20 percent of all women, and about half of all pregnant women have it as well. Meanwhile, only about 3 percent of men are iron deficient. The condition is also caused by low iron intake, gastrointestinal bleeding associated with ulcers, and the use of aspirin or nonsteroidal anti-inflammatory drugs.

Before true anemia develops, patients with mild iron deficiency will have a low ferritin level, which measures iron stores. Studies in the British Medical Journal found that low ferritin levels, even without anemia, are often found in patients with fatigue, which will easily improve with iron treatments. Dr. Friedman recommends iron treatment in people with a ferritin level below 50 ng/mL (nanograms per milliliter). He recommends taking enough iron to boost the ferritin level above 70 ng/mL.

Because iron deficiency is so common, many people must take iron supplements to build up their iron level. Pregnant women must also ingest higher amounts of iron, usually in a prenatal vitamin.


People with hypothyroidism who take iron supplements must be careful not to take their thyroid hormone replacement at the same time. In fact, they should take their thyroid medication first and take their iron at least four hours later. Taken together, iron can inhibit absorption of the thyroid medication.

In some people, even the ingestion of iron-rich foods can interfere with the absorption of thyroid medication. For that reason, you should always look at the iron content on food labels. Certain foods are iron-fortified and high in iron. For example, one serving of multi-grain Cheerios contains 100 percent of your daily value of iron.

While you shouldn't avoid taking iron or eating iron-rich foods, you may need to experiment to figure out which foods affect your symptoms of hypothyroidism. If you have a difficult time striking the right balance, consider talking to a registered dietitian or nutritionist about how to manage your iron intake along with your thyroid medication.

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