A Study of Vitamin B₁₂ Requirements in a Patient With Pernicious Anemia and Thyrotoxicosis: Evidence of an Increased Need for Vitamin B₁₂ in the Presence of Hyperthyroidism

The response to small doses of vitamin B₁₂ was studied in a woman with pernicious anemia and thyrotoxicosis. No response to 1 µg. per day occurred, but she did respond to 10 µg. per day. Fourteen months later when she was euthyroid, the patient did respond to 1 µg. per day. In another study, serum vitamin B₁₂ levels were significantly lower in a group of patients with hyperthyroidism than in a group of normal subjects. Seventeen of 20 patients with hyperthyroidism exhibited significantly higher serum vitamin B₁₂ levels 5-8 months after becoming euthyroid. The results of these studies provide evidence for increased vitamin B₁₂ requirements in the presence of hyperthyroidism. The greater need for vitamin B₁₂ appears to be related to increased utilization and/or accelerated turnover imposed by increased metabolism.