Numbness and Tingling Symptoms in Hypothyroidism May Be Due To Vitamin B12 Deficiency
Vitamin B12 deficiency is often associated with the most common form of hypothyroidism, autoimmune thyroid disease. In India, more than 50% of hypothyroid patients were found to be B12 deficient, but this is in a population with a much higher vegan/vegetarian diet compared to Taiwan that reported B12 deficiency in a little over 6% of those tested. The studies also don't always use the same laboratory cut-off levels for diagnosis, which is why the prevalence of B12 deficiency is reported over a wide range of 6.3% - 55%. Regardless of this, many experts in the field recommend screening for B12 deficiency in hypothyroid patients at diagnosis and periodically thereafter. People who have an under-active thyroid gland frequently complain of a variety of symptoms, but numbness, tingling and difficulty swallowing were most often reported by hypothyroid patients with vitamin B12 deficiency.
A study in India using 200 pg/ml as the blood level lower limit found 55% of hypothyroid patients were B12 deficient, whereas only 6.3% of Taiwanese patients were deficient with the same cut-off. An Israeli study found that 28% of their hypothyroid patients had B12 deficiency, but used the lower cut-off of 180 pg/ml, thereby potentially reporting an artificially low prevalence of B12 deficiency in their study group.