Vitamin B12 and Its Relationship with Thyroid-Stimulating Hormone (TSH)
Vitamin B12 deficiency can affect thyroid function by potentially lowering TSH levels, while hypothyroidism is associated with lower vitamin B12 levels. The relationship between vitamin B12 and thyroid function is bidirectional and clinically significant.
Impact of Vitamin B12 on TSH Levels
- Recent evidence shows that vitamin B12 deficiency is associated with decreased TSH levels in infants, suggesting a direct relationship between B12 status and thyroid function 1
- In a large-scale study of over 10,000 children, those with vitamin B12 deficiency had significantly lower TSH levels compared to children with normal B12 levels 1
- A positive correlation has been observed between TSH and hemoglobin levels in the context of B12 deficiency, indicating interconnected metabolic pathways 1
Impact of Thyroid Disorders on Vitamin B12 Status
- Patients with hypothyroidism have significantly lower vitamin B12 levels compared to healthy individuals (mean difference: -60.67 pg/mL) 2
- The frequency of vitamin B12 deficiency is approximately 27% among patients with hypothyroidism and subclinical hypothyroidism 2
- Autoimmune thyroid disease is associated with vitamin B12 deficiency in approximately 18% of cases 2
Autoimmune Connection
- There is a negative correlation between vitamin B12 levels and anti-thyroid peroxidase (anti-TPO) antibodies in patients with autoimmune hypothyroidism 3
- Both vitamin B12 and vitamin D deficiencies are associated with autoimmune hypothyroidism, suggesting common autoimmune mechanisms 3
- Vitamin B12 deficiency should be investigated at the time of diagnosis of autoimmune hypothyroidism and during follow-up appointments 3
Clinical Implications
- Screening for both vitamin B12 deficiency and thyroid disease is recommended, particularly in elderly populations, as early diagnosis can prevent serious conditions such as dementia, depression, or irreversible tissue damage 4
- In patients with type 1 diabetes, measurement of vitamin B12 levels should be considered when peripheral neuropathy or unexplained anemia is present, due to the increased risk of autoimmune comorbidities 5
- The cognitive lab panel recommended for evaluating cognitive-behavioral syndromes includes screening tests for both TSH and vitamin B12 deficiency, as both are common in older adults and can cause neuropsychiatric symptoms 5
Diagnostic Considerations
- When assessing vitamin B12 status, holotranscobalamin (HoloTC) has been shown to demonstrate greater sensitivity than serum cobalamin, particularly in older populations 5
- Metabolic B12 deficiency (serum B12 below 258 pmol/L with elevated plasma total homocysteine or methylmalonic acid) is frequently missed because a serum B12 in the normal range is often incorrectly accepted as ruling out B12 deficiency 5
- Homocysteine testing may be included in assessment because hyperhomocysteinemia is associated with functional B12 deficiency that may not always be readily detected by B12 levels in blood 5
Treatment Implications
- When vitamin B12 deficiency is identified in patients with thyroid disorders, supplementation should be considered to potentially improve both B12 status and thyroid function 3
- Certain medications (colchicine, H2 receptor antagonists, metformin, phenobarbital, pregabalin, primidone) can contribute to vitamin B12 deficiency and should be evaluated as potential causes in patients with thyroid disorders 6
- In patients with subclinical hypothyroidism, monitoring vitamin B12 status may be warranted, especially in those with TSH levels above 7 μIU/L or positive anti-TPO antibodies 7
The evidence clearly demonstrates a relationship between vitamin B12 and thyroid function, with deficiencies in one potentially affecting the other. Clinicians should consider this relationship when evaluating patients with either thyroid disorders or vitamin B12 deficiency.