Low Thyroid and Iron Deficiency: 6 Reasons So Many Women Experience Both

1. Iron Is Required for Thyroid Hormone Production

Iron plays a direct role in thyroid hormone production, storage and release.

The thyroid gland relies on an enzyme called thyroid peroxidase (TPO) to produce thyroid hormones. Iron is required for this enzyme to function properly [3].

If iron stores are too low, thyroid hormone production can slow down.

This doesn’t mean every woman with low ferritin will develop thyroid issues.

But it does mean iron status can quietly influence how well the thyroid works.

2. Low Ferritin Can Slow Thyroid Metabolism

Ferritin is the protein that stores iron inside the body.

Low ferritin levels often reflect depleted iron reserves. If you’re unfamiliar with ferritin and why it matters, you may find it helpful to read my article “5 Low Ferritin Reasons No One Explains (And Why Supplements Often Aren’t Enough).”

When ferritin drops too low, research shows thyroid hormone activity can become less efficient [4].

In practical terms, this may look like:

• feeling tired even after sleeping
• slower metabolism
• difficulty regulating body temperature
• lower overall energy

This overlap is why many women with fatigue feel stuck in a loop.

Iron affects thyroid activity. Thyroid activity affects energy production.

3. Gut Absorption Problems Affect Both

Your gut plays a major role in nutrient absorption.

Iron absorption happens primarily in the small intestine. Thyroid-supportive nutrients like selenium, zinc, iodine, and B vitamins are also absorbed through the digestive system.

When gut health is off, both systems can struggle.

Common contributors include:

• low stomach acid
• gut dysbiosis
• gluten sensitivity
• intestinal inflammation

This was a key piece of my own health journey. Once gut balance improved, nutrient absorption started improving too.

If your body cannot absorb nutrients well, it becomes harder to restore iron levels or support thyroid function.

4. Autoimmune Thyroid Conditions Increase Iron Deficiency Risk

Hashimoto’s thyroiditis is the most common cause of hypothyroidism in women.

It’s an autoimmune condition where the immune system targets thyroid tissue.

Autoimmune conditions often occur alongside digestive changes such as increased gut permeability or inflammation.

That environment can make nutrient deficiencies more likely.

Research also shows women with Hashimoto’s have higher rates of iron deficiency compared with the general population [5].

Iron becomes even more important in these situations because it supports thyroid hormone production and oxygen transport.

5. Chronic Inflammation Disrupts Both Systems

Inflammation affects how iron moves through the body.

During inflammation, the liver increases production of a hormone called hepcidin, which blocks iron absorption and traps iron in storage sites [6].

This means iron may be present in the body but unavailable for use.

Inflammation can also affect thyroid signaling and hormone conversion.

The result can look like:

• persistent fatigue
• poor recovery
• reduced energy production

Addressing underlying inflammation often becomes an important part of restoring balance.

6. Heavy Menstrual Cycles Linked With Thyroid Dysfunction

Heavy menstrual cycles are one of the most common causes of iron deficiency in women.

Thyroid hormones play a role in regulating the menstrual cycle.

When thyroid function slows, cycles can sometimes become heavier or longer.

More blood loss means more iron loss.

Over time this can slowly drain iron stores.

Women often assume heavy periods are just part of life.

Yet sometimes they reflect deeper hormonal or thyroid imbalances worth exploring.