Estimate how long it would take a strict vegan with no B12 intake to develop clinical deficiency assuming average liver B12 stores of 3000 µg and a physiological daily requirement (utilization/loss) of 2.5 µg per day. Show your calculation and final estimate in years.

• A. Approximately 3.3 years (about 1,200 days) before clinical deficiency would be expected.
• B. Less than 6 months, because liver stores deplete rapidly when no dietary intake occurs.
• C. Clinical deficiency would never occur because enterohepatic recycling of B12 fully compensates for lack of dietary intake indefinitely.
• D. Approximately 10–15 years, because daily requirements are only micrograms and stores are extremely large compared to needs.

Answer: (A)