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Can low B12 cause thyroid problems?

Low vitamin B12 levels can potentially lead to thyroid problems in some cases. Vitamin B12 plays an important role in proper thyroid function, so a deficiency can disrupt normal thyroid hormone production.

How B12 affects thyroid function

Vitamin B12 is needed for several aspects of thyroid hormone metabolism and regulation:

  • B12 is required for proper absorption of iodine, which is necessary for thyroid hormone synthesis.
  • B12 helps convert inactive T4 thyroid hormone into active T3 thyroid hormone.
  • B12 deficiency can lead to increased levels of homocysteine, which has been associated with thyroid dysfunction.
  • Low B12 status can cause reduced activity of thyroid peroxidase, an enzyme involved in thyroid hormone production.

Without adequate B12 levels, thyroid hormone synthesis and activation can be impaired. Over time, this can potentially lead to hypothyroidism in some cases.

Studies on B12 and thyroid function

Several studies have found connections between low B12 levels and altered thyroid hormone levels:

  • A study in over 3,000 adults found that those with B12 deficiency were more likely to have hypothyroidism.
  • Multiple studies have shown that thyroid hormone levels improve after vitamin B12 supplementation in those with deficiency.
  • One study found that 47% of people with autoimmune thyroid disease had low B12 levels.
  • Research shows a significant association between high homocysteine, low B12, and hypothyroidism.

The research suggests that optimizing B12 status could potentially help normalize thyroid hormone levels in those with deficiency.

Who is at risk?

Certain groups have an increased risk of both B12 deficiency and thyroid problems:

  • Older adults – The ability to absorb vitamin B12 decreases with age. Older adults are also more likely to develop hypothyroidism.
  • Vegetarians/vegans – Plant foods have no B12 unless fortified. Those who eat no animal products are at higher risk of deficiency.
  • People with autoimmunity – Autoimmune conditions like celiac disease and pernicious anemia increase the risk of B12 deficiency. Autoimmunity also underlies Hashimoto’s thyroiditis.
  • People with low stomach acid – Sufficient stomach acid is required to separate B12 from foods. Low acid levels increase the risk of deficiency.
  • Those with digestive disorders – Conditions like IBS or Crohn’s disease can impair B12 absorption from foods.
  • Pregnant women – Requirements for B12 increase during pregnancy, increasing needs.
  • Diabetics taking metformin – Metformin has been associated with reduced B12 absorption.

Symptoms of B12 deficiency

Low B12 can cause the following symptoms that may overlap with hypothyroidism:

  • Fatigue and weakness
  • Memory problems and brain fog
  • Tingling or numbness in hands and feet
  • Dizziness
  • Depression, anxiety and irritability
  • Hair loss

If you have symptoms of a thyroid disorder along with symptoms of B12 deficiency, it’s important to get tested for both.

Testing B12 levels

Blood tests can check B12 levels and identify a deficiency. Normal lab ranges are:

B12 Level Status
Above 300 pg/mL Normal
200-300 pg/mL Borderline deficiency
Under 200 pg/mL Deficiency

The methylmalonic acid (MMA) blood test can also help confirm B12 deficiency. High MMA levels are indicative of deficiency.

Treatment for low B12

Treating an underlying B12 deficiency may help optimize thyroid hormone levels in some cases. Treatment options include:

  • B12 supplements – Cyanocobalamin or methylcobalamin supplements taken daily or weekly.
  • B12 injections – Intramuscular injections especially beneficial for those with absorption issues.
  • Improved diet – Increasing intake of B12-rich foods like meat, eggs, dairy and fortified foods.
  • Treat underlying condition – Addressing low stomach acid, autoimmunity, IBS, etc., if present.

Work with your healthcare provider to determine the optimal type and dose of B12 for your needs.

Thyroid medications

Normalizing B12 levels may help improve thyroid function in some cases. However, it likely won’t resolve all thyroid problems if an underlying disorder like Hashimoto’s is present. Thyroid medications like levothyroxine are still often required to treat hypothyroidism and control symptoms.

Other nutritional factors

In addition to B12, other nutrients play a role in thyroid function including:

  • Iodine
  • Iron
  • Selenium
  • Zinc
  • Vitamin D

A balanced diet with sufficient intake of these nutrients provides the best support for healthy thyroid hormone levels.

The bottom line

In summary, vitamin B12 deficiency can potentially contribute to thyroid problems in some cases. Groups most at risk include older adults, vegetarians, and those with absorption issues or autoimmunity. Testing B12 levels in individuals with thyroid dysfunction and symptoms of deficiency can identify cases that may benefit from B12 supplementation. However, thyroid medications are still often needed even if B12 levels are addressed.